blob: d45e961515c13a545f61fc5cf0fc26aad84cc701 [file] [log] [blame]
Paul E. McKenneyf41d9112009-08-22 13:56:52 -07001/*
2 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
3 * Internal non-public definitions that provide either classic
Paul E. McKenney6cc68792011-03-02 13:15:15 -08004 * or preemptible semantics.
Paul E. McKenneyf41d9112009-08-22 13:56:52 -07005 *
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or
9 * (at your option) any later version.
10 *
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
15 *
16 * You should have received a copy of the GNU General Public License
Paul E. McKenney87de1cf2013-12-03 10:02:52 -080017 * along with this program; if not, you can access it online at
18 * http://www.gnu.org/licenses/gpl-2.0.html.
Paul E. McKenneyf41d9112009-08-22 13:56:52 -070019 *
20 * Copyright Red Hat, 2009
21 * Copyright IBM Corporation, 2009
22 *
23 * Author: Ingo Molnar <mingo@elte.hu>
24 * Paul E. McKenney <paulmck@linux.vnet.ibm.com>
25 */
26
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -080027#include <linux/delay.h>
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -070028#include <linux/gfp.h>
Paul E. McKenneyb626c1b2012-06-11 17:39:43 -070029#include <linux/oom.h>
Paul E. McKenney62ab7072012-07-16 10:42:38 +000030#include <linux/smpboot.h>
Paul E. McKenney4102ada2013-10-08 20:23:47 -070031#include "../time/tick-internal.h"
Paul E. McKenneyf41d9112009-08-22 13:56:52 -070032
Mike Galbraith5b61b0b2011-08-19 11:39:11 -070033#ifdef CONFIG_RCU_BOOST
Paul E. McKenney61cfd092014-09-02 12:30:58 -070034
Paul E. McKenneyabaa93d2014-06-12 13:30:25 -070035#include "../locking/rtmutex_common.h"
Clark Williams21871d72014-09-12 21:21:09 -050036
Paul E. McKenney61cfd092014-09-02 12:30:58 -070037/*
38 * Control variables for per-CPU and per-rcu_node kthreads. These
39 * handle all flavors of RCU.
40 */
41static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
42DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
43DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
44DEFINE_PER_CPU(char, rcu_cpu_has_work);
45
Clark Williams21871d72014-09-12 21:21:09 -050046#endif /* #ifdef CONFIG_RCU_BOOST */
Mike Galbraith5b61b0b2011-08-19 11:39:11 -070047
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -070048#ifdef CONFIG_RCU_NOCB_CPU
49static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
50static bool have_rcu_nocb_mask; /* Was rcu_nocb_mask allocated? */
Paul Gortmaker1b0048a2012-12-20 13:19:22 -080051static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -070052#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
53
Paul E. McKenney26845c22010-04-13 14:19:23 -070054/*
55 * Check the RCU kernel configuration parameters and print informative
56 * messages about anything out of the ordinary. If you like #ifdef, you
57 * will love this function.
58 */
59static void __init rcu_bootup_announce_oddness(void)
60{
61#ifdef CONFIG_RCU_TRACE
Paul E. McKenneyefc151c2013-03-18 16:24:11 -070062 pr_info("\tRCU debugfs-based tracing is enabled.\n");
Paul E. McKenney26845c22010-04-13 14:19:23 -070063#endif
64#if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
Paul E. McKenneyefc151c2013-03-18 16:24:11 -070065 pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
Paul E. McKenney26845c22010-04-13 14:19:23 -070066 CONFIG_RCU_FANOUT);
67#endif
68#ifdef CONFIG_RCU_FANOUT_EXACT
Paul E. McKenneyefc151c2013-03-18 16:24:11 -070069 pr_info("\tHierarchical RCU autobalancing is disabled.\n");
Paul E. McKenney26845c22010-04-13 14:19:23 -070070#endif
71#ifdef CONFIG_RCU_FAST_NO_HZ
Paul E. McKenneyefc151c2013-03-18 16:24:11 -070072 pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
Paul E. McKenney26845c22010-04-13 14:19:23 -070073#endif
74#ifdef CONFIG_PROVE_RCU
Paul E. McKenneyefc151c2013-03-18 16:24:11 -070075 pr_info("\tRCU lockdep checking is enabled.\n");
Paul E. McKenney26845c22010-04-13 14:19:23 -070076#endif
77#ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
Paul E. McKenneyefc151c2013-03-18 16:24:11 -070078 pr_info("\tRCU torture testing starts during boot.\n");
Paul E. McKenney26845c22010-04-13 14:19:23 -070079#endif
Paul E. McKenneya858af22012-01-16 13:29:10 -080080#if defined(CONFIG_RCU_CPU_STALL_INFO)
Paul E. McKenneyefc151c2013-03-18 16:24:11 -070081 pr_info("\tAdditional per-CPU info printed with stalls.\n");
Paul E. McKenney26845c22010-04-13 14:19:23 -070082#endif
83#if NUM_RCU_LVL_4 != 0
Paul E. McKenneyefc151c2013-03-18 16:24:11 -070084 pr_info("\tFour-level hierarchy is enabled.\n");
Paul E. McKenney26845c22010-04-13 14:19:23 -070085#endif
Paul E. McKenneyf885b7f2012-04-23 15:52:53 -070086 if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF)
Paul E. McKenney9a5739d2013-03-28 20:48:36 -070087 pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
Paul E. McKenneycca6f392012-05-08 21:00:28 -070088 if (nr_cpu_ids != NR_CPUS)
Paul E. McKenneyefc151c2013-03-18 16:24:11 -070089 pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
Clark Williams21871d72014-09-12 21:21:09 -050090#ifdef CONFIG_RCU_BOOST
91 pr_info("\tRCU kthread priority: %d.\n", kthread_prio);
92#endif
Paul E. McKenney26845c22010-04-13 14:19:23 -070093}
94
Pranith Kumar28f65692014-09-22 14:00:48 -040095#ifdef CONFIG_PREEMPT_RCU
Paul E. McKenneyf41d9112009-08-22 13:56:52 -070096
Steven Rostedt (Red Hat)a41bfeb2013-07-12 17:00:28 -040097RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu);
Uma Sharmae5341652014-03-23 22:32:09 -070098static struct rcu_state *rcu_state_p = &rcu_preempt_state;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -070099
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800100static int rcu_preempted_readers_exp(struct rcu_node *rnp);
Paul E. McKenneyd19fb8d2014-10-31 12:56:16 -0700101static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
102 bool wake);
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800103
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700104/*
105 * Tell them what RCU they are running.
106 */
Paul E. McKenney0e0fc1c2009-11-11 11:28:06 -0800107static void __init rcu_bootup_announce(void)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700108{
Paul E. McKenneyefc151c2013-03-18 16:24:11 -0700109 pr_info("Preemptible hierarchical RCU implementation.\n");
Paul E. McKenney26845c22010-04-13 14:19:23 -0700110 rcu_bootup_announce_oddness();
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700111}
112
113/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800114 * Record a preemptible-RCU quiescent state for the specified CPU. Note
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700115 * that this just means that the task currently running on the CPU is
116 * not in a quiescent state. There might be any number of tasks blocked
117 * while in an RCU read-side critical section.
Paul E. McKenney25502a62010-04-01 17:37:01 -0700118 *
Paul E. McKenney1d082fd2014-08-14 16:01:53 -0700119 * As with the other rcu_*_qs() functions, callers to this function
120 * must disable preemption.
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700121 */
Paul E. McKenney284a8c92014-08-14 16:38:46 -0700122static void rcu_preempt_qs(void)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700123{
Paul E. McKenney284a8c92014-08-14 16:38:46 -0700124 if (!__this_cpu_read(rcu_preempt_data.passed_quiesce)) {
125 trace_rcu_grace_period(TPS("rcu_preempt"),
126 __this_cpu_read(rcu_preempt_data.gpnum),
127 TPS("cpuqs"));
128 __this_cpu_write(rcu_preempt_data.passed_quiesce, 1);
129 barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */
130 current->rcu_read_unlock_special.b.need_qs = false;
131 }
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700132}
133
134/*
Paul E. McKenneyc3422be2009-09-13 09:15:10 -0700135 * We have entered the scheduler, and the current task might soon be
136 * context-switched away from. If this task is in an RCU read-side
137 * critical section, we will no longer be able to rely on the CPU to
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800138 * record that fact, so we enqueue the task on the blkd_tasks list.
139 * The task will dequeue itself when it exits the outermost enclosing
140 * RCU read-side critical section. Therefore, the current grace period
141 * cannot be permitted to complete until the blkd_tasks list entries
142 * predating the current grace period drain, in other words, until
143 * rnp->gp_tasks becomes NULL.
Paul E. McKenneyc3422be2009-09-13 09:15:10 -0700144 *
145 * Caller must disable preemption.
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700146 */
Paul E. McKenney38200cf2014-10-21 12:50:04 -0700147static void rcu_preempt_note_context_switch(void)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700148{
149 struct task_struct *t = current;
Paul E. McKenneyc3422be2009-09-13 09:15:10 -0700150 unsigned long flags;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700151 struct rcu_data *rdp;
152 struct rcu_node *rnp;
153
Paul E. McKenney10f39bb2011-07-17 21:14:35 -0700154 if (t->rcu_read_lock_nesting > 0 &&
Paul E. McKenney1d082fd2014-08-14 16:01:53 -0700155 !t->rcu_read_unlock_special.b.blocked) {
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700156
157 /* Possibly blocking in an RCU read-side critical section. */
Paul E. McKenney38200cf2014-10-21 12:50:04 -0700158 rdp = this_cpu_ptr(rcu_preempt_state.rda);
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700159 rnp = rdp->mynode;
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800160 raw_spin_lock_irqsave(&rnp->lock, flags);
Paul E. McKenney6303b9c2013-12-11 13:59:10 -0800161 smp_mb__after_unlock_lock();
Paul E. McKenney1d082fd2014-08-14 16:01:53 -0700162 t->rcu_read_unlock_special.b.blocked = true;
Paul E. McKenney86848962009-08-27 15:00:12 -0700163 t->rcu_blocked_node = rnp;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700164
165 /*
166 * If this CPU has already checked in, then this task
167 * will hold up the next grace period rather than the
168 * current grace period. Queue the task accordingly.
169 * If the task is queued for the current grace period
170 * (i.e., this CPU has not yet passed through a quiescent
171 * state for the current grace period), then as long
172 * as that task remains queued, the current grace period
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800173 * cannot end. Note that there is some uncertainty as
174 * to exactly when the current grace period started.
175 * We take a conservative approach, which can result
176 * in unnecessarily waiting on tasks that started very
177 * slightly after the current grace period began. C'est
178 * la vie!!!
Paul E. McKenneyb0e165c2009-09-13 09:15:09 -0700179 *
180 * But first, note that the current CPU must still be
181 * on line!
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700182 */
Paul E. McKenney0aa04b02015-01-23 21:52:37 -0800183 WARN_ON_ONCE((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0);
Paul E. McKenneye7d88422009-09-18 09:50:18 -0700184 WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800185 if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) {
186 list_add(&t->rcu_node_entry, rnp->gp_tasks->prev);
187 rnp->gp_tasks = &t->rcu_node_entry;
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800188#ifdef CONFIG_RCU_BOOST
189 if (rnp->boost_tasks != NULL)
190 rnp->boost_tasks = rnp->gp_tasks;
191#endif /* #ifdef CONFIG_RCU_BOOST */
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800192 } else {
193 list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
194 if (rnp->qsmask & rdp->grpmask)
195 rnp->gp_tasks = &t->rcu_node_entry;
196 }
Paul E. McKenneyd4c08f22011-06-25 06:36:56 -0700197 trace_rcu_preempt_task(rdp->rsp->name,
198 t->pid,
199 (rnp->qsmask & rdp->grpmask)
200 ? rnp->gpnum
201 : rnp->gpnum + 1);
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800202 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenney10f39bb2011-07-17 21:14:35 -0700203 } else if (t->rcu_read_lock_nesting < 0 &&
Paul E. McKenney1d082fd2014-08-14 16:01:53 -0700204 t->rcu_read_unlock_special.s) {
Paul E. McKenney10f39bb2011-07-17 21:14:35 -0700205
206 /*
207 * Complete exit from RCU read-side critical section on
208 * behalf of preempted instance of __rcu_read_unlock().
209 */
210 rcu_read_unlock_special(t);
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700211 }
212
213 /*
214 * Either we were not in an RCU read-side critical section to
215 * begin with, or we have now recorded that critical section
216 * globally. Either way, we can now note a quiescent state
217 * for this CPU. Again, if we were in an RCU read-side critical
218 * section, and if that critical section was blocking the current
219 * grace period, then the fact that the task has been enqueued
220 * means that we continue to block the current grace period.
221 */
Paul E. McKenney284a8c92014-08-14 16:38:46 -0700222 rcu_preempt_qs();
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700223}
224
225/*
Paul E. McKenneyfc2219d2009-09-23 09:50:41 -0700226 * Check for preempted RCU readers blocking the current grace period
227 * for the specified rcu_node structure. If the caller needs a reliable
228 * answer, it must hold the rcu_node's ->lock.
229 */
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800230static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
Paul E. McKenneyfc2219d2009-09-23 09:50:41 -0700231{
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800232 return rnp->gp_tasks != NULL;
Paul E. McKenneyfc2219d2009-09-23 09:50:41 -0700233}
234
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800235/*
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800236 * Advance a ->blkd_tasks-list pointer to the next entry, instead
237 * returning NULL if at the end of the list.
238 */
239static struct list_head *rcu_next_node_entry(struct task_struct *t,
240 struct rcu_node *rnp)
241{
242 struct list_head *np;
243
244 np = t->rcu_node_entry.next;
245 if (np == &rnp->blkd_tasks)
246 np = NULL;
247 return np;
248}
249
250/*
Paul E. McKenney8af3a5e2014-10-31 11:22:37 -0700251 * Return true if the specified rcu_node structure has tasks that were
252 * preempted within an RCU read-side critical section.
253 */
254static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
255{
256 return !list_empty(&rnp->blkd_tasks);
257}
258
259/*
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800260 * Handle special cases during rcu_read_unlock(), such as needing to
261 * notify RCU core processing or task having blocked during the RCU
262 * read-side critical section.
263 */
Paul E. McKenney2a3fa842012-05-21 11:58:36 -0700264void rcu_read_unlock_special(struct task_struct *t)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700265{
Paul E. McKenneyb6a932d2014-10-31 12:05:04 -0700266 bool empty_exp;
267 bool empty_norm;
268 bool empty_exp_now;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700269 unsigned long flags;
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800270 struct list_head *np;
Paul E. McKenney82e78d82011-08-04 07:55:34 -0700271#ifdef CONFIG_RCU_BOOST
Paul E. McKenneyabaa93d2014-06-12 13:30:25 -0700272 bool drop_boost_mutex = false;
Paul E. McKenney82e78d82011-08-04 07:55:34 -0700273#endif /* #ifdef CONFIG_RCU_BOOST */
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700274 struct rcu_node *rnp;
Paul E. McKenney1d082fd2014-08-14 16:01:53 -0700275 union rcu_special special;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700276
277 /* NMI handlers cannot block and cannot safely manipulate state. */
278 if (in_nmi())
279 return;
280
281 local_irq_save(flags);
282
283 /*
284 * If RCU core is waiting for this CPU to exit critical section,
Paul E. McKenney1d082fd2014-08-14 16:01:53 -0700285 * let it know that we have done so. Because irqs are disabled,
286 * t->rcu_read_unlock_special cannot change.
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700287 */
288 special = t->rcu_read_unlock_special;
Paul E. McKenney1d082fd2014-08-14 16:01:53 -0700289 if (special.b.need_qs) {
Paul E. McKenney284a8c92014-08-14 16:38:46 -0700290 rcu_preempt_qs();
Paul E. McKenneyc0135d02015-01-22 22:47:14 -0800291 t->rcu_read_unlock_special.b.need_qs = false;
Paul E. McKenney1d082fd2014-08-14 16:01:53 -0700292 if (!t->rcu_read_unlock_special.s) {
Lai Jiangshan79a62f92013-10-30 04:13:22 -0700293 local_irq_restore(flags);
294 return;
295 }
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700296 }
297
Lai Jiangshan79a62f92013-10-30 04:13:22 -0700298 /* Hardware IRQ handlers cannot block, complain if they get here. */
299 if (WARN_ON_ONCE(in_irq() || in_serving_softirq())) {
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700300 local_irq_restore(flags);
301 return;
302 }
303
304 /* Clean up if blocked during RCU read-side critical section. */
Paul E. McKenney1d082fd2014-08-14 16:01:53 -0700305 if (special.b.blocked) {
306 t->rcu_read_unlock_special.b.blocked = false;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700307
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700308 /*
309 * Remove this task from the list it blocked on. The
310 * task can migrate while we acquire the lock, but at
311 * most one time. So at most two passes through loop.
312 */
313 for (;;) {
Paul E. McKenney86848962009-08-27 15:00:12 -0700314 rnp = t->rcu_blocked_node;
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800315 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
Paul E. McKenney6303b9c2013-12-11 13:59:10 -0800316 smp_mb__after_unlock_lock();
Paul E. McKenney86848962009-08-27 15:00:12 -0700317 if (rnp == t->rcu_blocked_node)
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700318 break;
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800319 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700320 }
Paul E. McKenney74e871a2014-10-30 21:08:53 -0700321 empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800322 empty_exp = !rcu_preempted_readers_exp(rnp);
323 smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800324 np = rcu_next_node_entry(t, rnp);
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700325 list_del_init(&t->rcu_node_entry);
Paul E. McKenney82e78d82011-08-04 07:55:34 -0700326 t->rcu_blocked_node = NULL;
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -0400327 trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
Paul E. McKenneyd4c08f22011-06-25 06:36:56 -0700328 rnp->gpnum, t->pid);
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800329 if (&t->rcu_node_entry == rnp->gp_tasks)
330 rnp->gp_tasks = np;
331 if (&t->rcu_node_entry == rnp->exp_tasks)
332 rnp->exp_tasks = np;
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800333#ifdef CONFIG_RCU_BOOST
334 if (&t->rcu_node_entry == rnp->boost_tasks)
335 rnp->boost_tasks = np;
Paul E. McKenneyabaa93d2014-06-12 13:30:25 -0700336 /* Snapshot ->boost_mtx ownership with rcu_node lock held. */
337 drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800338#endif /* #ifdef CONFIG_RCU_BOOST */
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700339
340 /*
341 * If this was the last task on the current list, and if
342 * we aren't waiting on any CPUs, report the quiescent state.
Paul E. McKenney389abd42011-09-21 14:41:37 -0700343 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
344 * so we must take a snapshot of the expedited state.
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700345 */
Paul E. McKenney389abd42011-09-21 14:41:37 -0700346 empty_exp_now = !rcu_preempted_readers_exp(rnp);
Paul E. McKenney74e871a2014-10-30 21:08:53 -0700347 if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) {
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -0400348 trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
Paul E. McKenneyd4c08f22011-06-25 06:36:56 -0700349 rnp->gpnum,
350 0, rnp->qsmask,
351 rnp->level,
352 rnp->grplo,
353 rnp->grphi,
354 !!rnp->gp_tasks);
Paul E. McKenneycc99a312015-02-23 08:59:29 -0800355 rcu_report_unblock_qs_rnp(&rcu_preempt_state,
356 rnp, flags);
Paul E. McKenneyc701d5d2012-06-28 08:08:25 -0700357 } else {
Paul E. McKenneyd4c08f22011-06-25 06:36:56 -0700358 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenneyc701d5d2012-06-28 08:08:25 -0700359 }
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800360
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800361#ifdef CONFIG_RCU_BOOST
362 /* Unboost if we were boosted. */
Lai Jiangshanabaf3f92014-11-18 16:30:01 +0800363 if (drop_boost_mutex)
Paul E. McKenneyabaa93d2014-06-12 13:30:25 -0700364 rt_mutex_unlock(&rnp->boost_mtx);
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800365#endif /* #ifdef CONFIG_RCU_BOOST */
366
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800367 /*
368 * If this was the last task on the expedited lists,
369 * then we need to report up the rcu_node hierarchy.
370 */
Paul E. McKenney389abd42011-09-21 14:41:37 -0700371 if (!empty_exp && empty_exp_now)
Thomas Gleixnerb40d2932011-10-22 07:12:34 -0700372 rcu_report_exp_rnp(&rcu_preempt_state, rnp, true);
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800373 } else {
374 local_irq_restore(flags);
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700375 }
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700376}
377
Paul E. McKenney1ed509a2010-02-22 17:05:05 -0800378/*
379 * Dump detailed information for all tasks blocking the current RCU
380 * grace period on the specified rcu_node structure.
381 */
382static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
383{
384 unsigned long flags;
Paul E. McKenney1ed509a2010-02-22 17:05:05 -0800385 struct task_struct *t;
386
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800387 raw_spin_lock_irqsave(&rnp->lock, flags);
Paul E. McKenney5fd4dc02012-08-10 16:00:11 -0700388 if (!rcu_preempt_blocked_readers_cgp(rnp)) {
389 raw_spin_unlock_irqrestore(&rnp->lock, flags);
390 return;
391 }
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800392 t = list_entry(rnp->gp_tasks,
393 struct task_struct, rcu_node_entry);
394 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
395 sched_show_task(t);
396 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenney1ed509a2010-02-22 17:05:05 -0800397}
398
399/*
400 * Dump detailed information for all tasks blocking the current RCU
401 * grace period.
402 */
403static void rcu_print_detail_task_stall(struct rcu_state *rsp)
404{
405 struct rcu_node *rnp = rcu_get_root(rsp);
406
407 rcu_print_detail_task_stall_rnp(rnp);
408 rcu_for_each_leaf_node(rsp, rnp)
409 rcu_print_detail_task_stall_rnp(rnp);
410}
411
Paul E. McKenneya858af22012-01-16 13:29:10 -0800412#ifdef CONFIG_RCU_CPU_STALL_INFO
413
414static void rcu_print_task_stall_begin(struct rcu_node *rnp)
415{
Paul E. McKenneyefc151c2013-03-18 16:24:11 -0700416 pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
Paul E. McKenneya858af22012-01-16 13:29:10 -0800417 rnp->level, rnp->grplo, rnp->grphi);
418}
419
420static void rcu_print_task_stall_end(void)
421{
Paul E. McKenneyefc151c2013-03-18 16:24:11 -0700422 pr_cont("\n");
Paul E. McKenneya858af22012-01-16 13:29:10 -0800423}
424
425#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
426
427static void rcu_print_task_stall_begin(struct rcu_node *rnp)
428{
429}
430
431static void rcu_print_task_stall_end(void)
432{
433}
434
435#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
436
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700437/*
438 * Scan the current list of tasks blocked within RCU read-side critical
439 * sections, printing out the tid of each.
440 */
Paul E. McKenney9bc8b552011-08-13 13:31:47 -0700441static int rcu_print_task_stall(struct rcu_node *rnp)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700442{
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700443 struct task_struct *t;
Paul E. McKenney9bc8b552011-08-13 13:31:47 -0700444 int ndetected = 0;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700445
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800446 if (!rcu_preempt_blocked_readers_cgp(rnp))
Paul E. McKenney9bc8b552011-08-13 13:31:47 -0700447 return 0;
Paul E. McKenneya858af22012-01-16 13:29:10 -0800448 rcu_print_task_stall_begin(rnp);
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800449 t = list_entry(rnp->gp_tasks,
450 struct task_struct, rcu_node_entry);
Paul E. McKenney9bc8b552011-08-13 13:31:47 -0700451 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
Paul E. McKenneyefc151c2013-03-18 16:24:11 -0700452 pr_cont(" P%d", t->pid);
Paul E. McKenney9bc8b552011-08-13 13:31:47 -0700453 ndetected++;
454 }
Paul E. McKenneya858af22012-01-16 13:29:10 -0800455 rcu_print_task_stall_end();
Paul E. McKenney9bc8b552011-08-13 13:31:47 -0700456 return ndetected;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700457}
458
Paul E. McKenney53d84e02010-08-10 14:28:53 -0700459/*
Paul E. McKenneyb0e165c2009-09-13 09:15:09 -0700460 * Check that the list of blocked tasks for the newly completed grace
461 * period is in fact empty. It is a serious bug to complete a grace
462 * period that still has RCU readers blocked! This function must be
463 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
464 * must be held by the caller.
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800465 *
466 * Also, if there are blocked tasks on the list, they automatically
467 * block the newly created grace period, so set up ->gp_tasks accordingly.
Paul E. McKenneyb0e165c2009-09-13 09:15:09 -0700468 */
469static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
470{
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800471 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
Paul E. McKenney96e92022014-10-31 14:09:23 -0700472 if (rcu_preempt_has_tasks(rnp))
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800473 rnp->gp_tasks = rnp->blkd_tasks.next;
Paul E. McKenney28ecd582009-09-18 09:50:17 -0700474 WARN_ON_ONCE(rnp->qsmask);
Paul E. McKenneyb0e165c2009-09-13 09:15:09 -0700475}
476
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700477/*
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700478 * Check for a quiescent state from the current CPU. When a task blocks,
479 * the task is recorded in the corresponding CPU's rcu_node structure,
480 * which is checked elsewhere.
481 *
482 * Caller must disable hard irqs.
483 */
Paul E. McKenney86aea0e2014-10-21 08:12:00 -0700484static void rcu_preempt_check_callbacks(void)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700485{
486 struct task_struct *t = current;
487
488 if (t->rcu_read_lock_nesting == 0) {
Paul E. McKenney284a8c92014-08-14 16:38:46 -0700489 rcu_preempt_qs();
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700490 return;
491 }
Paul E. McKenney10f39bb2011-07-17 21:14:35 -0700492 if (t->rcu_read_lock_nesting > 0 &&
Paul E. McKenney86aea0e2014-10-21 08:12:00 -0700493 __this_cpu_read(rcu_preempt_data.qs_pending) &&
494 !__this_cpu_read(rcu_preempt_data.passed_quiesce))
Paul E. McKenney1d082fd2014-08-14 16:01:53 -0700495 t->rcu_read_unlock_special.b.need_qs = true;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700496}
497
Paul E. McKenneya46e0892011-06-15 15:47:09 -0700498#ifdef CONFIG_RCU_BOOST
499
Shaohua Li09223372011-06-14 13:26:25 +0800500static void rcu_preempt_do_callbacks(void)
501{
Christoph Lameterc9d4b0a2013-08-31 13:34:10 -0700502 rcu_do_batch(&rcu_preempt_state, this_cpu_ptr(&rcu_preempt_data));
Shaohua Li09223372011-06-14 13:26:25 +0800503}
504
Paul E. McKenneya46e0892011-06-15 15:47:09 -0700505#endif /* #ifdef CONFIG_RCU_BOOST */
506
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700507/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800508 * Queue a preemptible-RCU callback for invocation after a grace period.
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700509 */
510void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
511{
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -0700512 __call_rcu(head, func, &rcu_preempt_state, -1, 0);
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700513}
514EXPORT_SYMBOL_GPL(call_rcu);
515
Paul E. McKenney6ebb2372009-11-22 08:53:50 -0800516/**
517 * synchronize_rcu - wait until a grace period has elapsed.
518 *
519 * Control will return to the caller some time after a full grace
520 * period has elapsed, in other words after all currently executing RCU
Paul E. McKenney77d84852010-07-08 17:38:59 -0700521 * read-side critical sections have completed. Note, however, that
522 * upon return from synchronize_rcu(), the caller might well be executing
523 * concurrently with new RCU read-side critical sections that began while
524 * synchronize_rcu() was waiting. RCU read-side critical sections are
525 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
Paul E. McKenneyf0a0e6f2012-10-23 13:47:01 -0700526 *
527 * See the description of synchronize_sched() for more detailed information
528 * on memory ordering guarantees.
Paul E. McKenney6ebb2372009-11-22 08:53:50 -0800529 */
530void synchronize_rcu(void)
531{
Paul E. McKenneyfe15d702012-01-04 13:30:33 -0800532 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
533 !lock_is_held(&rcu_lock_map) &&
534 !lock_is_held(&rcu_sched_lock_map),
535 "Illegal synchronize_rcu() in RCU read-side critical section");
Paul E. McKenney6ebb2372009-11-22 08:53:50 -0800536 if (!rcu_scheduler_active)
537 return;
Antti P Miettinen3705b882012-10-05 09:59:15 +0300538 if (rcu_expedited)
539 synchronize_rcu_expedited();
540 else
541 wait_rcu_gp(call_rcu);
Paul E. McKenney6ebb2372009-11-22 08:53:50 -0800542}
543EXPORT_SYMBOL_GPL(synchronize_rcu);
544
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800545static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
Paul E. McKenneybcfa57c2012-07-23 16:03:51 -0700546static unsigned long sync_rcu_preempt_exp_count;
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800547static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
548
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700549/*
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800550 * Return non-zero if there are any tasks in RCU read-side critical
551 * sections blocking the current preemptible-RCU expedited grace period.
552 * If there is no preemptible-RCU expedited grace period currently in
553 * progress, returns zero unconditionally.
554 */
555static int rcu_preempted_readers_exp(struct rcu_node *rnp)
556{
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800557 return rnp->exp_tasks != NULL;
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800558}
559
560/*
561 * return non-zero if there is no RCU expedited grace period in progress
562 * for the specified rcu_node structure, in other words, if all CPUs and
563 * tasks covered by the specified rcu_node structure have done their bit
564 * for the current expedited grace period. Works only for preemptible
565 * RCU -- other RCU implementation use other means.
566 *
567 * Caller must hold sync_rcu_preempt_exp_mutex.
568 */
569static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
570{
571 return !rcu_preempted_readers_exp(rnp) &&
572 ACCESS_ONCE(rnp->expmask) == 0;
573}
574
575/*
576 * Report the exit from RCU read-side critical section for the last task
577 * that queued itself during or before the current expedited preemptible-RCU
578 * grace period. This event is reported either to the rcu_node structure on
579 * which the task was queued or to one of that rcu_node structure's ancestors,
580 * recursively up the tree. (Calm down, calm down, we do the recursion
581 * iteratively!)
582 *
583 * Caller must hold sync_rcu_preempt_exp_mutex.
584 */
Thomas Gleixnerb40d2932011-10-22 07:12:34 -0700585static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
586 bool wake)
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800587{
588 unsigned long flags;
589 unsigned long mask;
590
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800591 raw_spin_lock_irqsave(&rnp->lock, flags);
Paul E. McKenney6303b9c2013-12-11 13:59:10 -0800592 smp_mb__after_unlock_lock();
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800593 for (;;) {
Paul E. McKenney131906b2011-07-17 02:05:49 -0700594 if (!sync_rcu_preempt_exp_done(rnp)) {
595 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800596 break;
Paul E. McKenney131906b2011-07-17 02:05:49 -0700597 }
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800598 if (rnp->parent == NULL) {
Paul E. McKenney131906b2011-07-17 02:05:49 -0700599 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenney78e4bc32013-09-24 15:04:06 -0700600 if (wake) {
601 smp_mb(); /* EGP done before wake_up(). */
Thomas Gleixnerb40d2932011-10-22 07:12:34 -0700602 wake_up(&sync_rcu_preempt_exp_wq);
Paul E. McKenney78e4bc32013-09-24 15:04:06 -0700603 }
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800604 break;
605 }
606 mask = rnp->grpmask;
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800607 raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800608 rnp = rnp->parent;
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800609 raw_spin_lock(&rnp->lock); /* irqs already disabled */
Paul E. McKenney6303b9c2013-12-11 13:59:10 -0800610 smp_mb__after_unlock_lock();
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800611 rnp->expmask &= ~mask;
612 }
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800613}
614
615/*
616 * Snapshot the tasks blocking the newly started preemptible-RCU expedited
Paul E. McKenney8eb74b22015-02-13 10:52:28 -0800617 * grace period for the specified rcu_node structure, phase 1. If there
618 * are such tasks, set the ->expmask bits up the rcu_node tree and also
619 * set the ->expmask bits on the leaf rcu_node structures to tell phase 2
620 * that work is needed here.
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800621 *
Paul E. McKenney8eb74b22015-02-13 10:52:28 -0800622 * Caller must hold sync_rcu_preempt_exp_mutex.
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800623 */
624static void
Paul E. McKenney8eb74b22015-02-13 10:52:28 -0800625sync_rcu_preempt_exp_init1(struct rcu_state *rsp, struct rcu_node *rnp)
626{
627 unsigned long flags;
628 unsigned long mask;
629 struct rcu_node *rnp_up;
630
631 raw_spin_lock_irqsave(&rnp->lock, flags);
632 smp_mb__after_unlock_lock();
633 WARN_ON_ONCE(rnp->expmask);
634 WARN_ON_ONCE(rnp->exp_tasks);
635 if (!rcu_preempt_has_tasks(rnp)) {
636 /* No blocked tasks, nothing to do. */
637 raw_spin_unlock_irqrestore(&rnp->lock, flags);
638 return;
639 }
640 /* Call for Phase 2 and propagate ->expmask bits up the tree. */
641 rnp->expmask = 1;
642 rnp_up = rnp;
643 while (rnp_up->parent) {
644 mask = rnp_up->grpmask;
645 rnp_up = rnp_up->parent;
646 if (rnp_up->expmask & mask)
647 break;
648 raw_spin_lock(&rnp_up->lock); /* irqs already off */
649 smp_mb__after_unlock_lock();
650 rnp_up->expmask |= mask;
651 raw_spin_unlock(&rnp_up->lock); /* irqs still off */
652 }
653 raw_spin_unlock_irqrestore(&rnp->lock, flags);
654}
655
656/*
657 * Snapshot the tasks blocking the newly started preemptible-RCU expedited
658 * grace period for the specified rcu_node structure, phase 2. If the
659 * leaf rcu_node structure has its ->expmask field set, check for tasks.
660 * If there are some, clear ->expmask and set ->exp_tasks accordingly,
661 * then initiate RCU priority boosting. Otherwise, clear ->expmask and
662 * invoke rcu_report_exp_rnp() to clear out the upper-level ->expmask bits,
663 * enabling rcu_read_unlock_special() to do the bit-clearing.
664 *
665 * Caller must hold sync_rcu_preempt_exp_mutex.
666 */
667static void
668sync_rcu_preempt_exp_init2(struct rcu_state *rsp, struct rcu_node *rnp)
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800669{
Paul E. McKenney1217ed12011-05-04 21:43:49 -0700670 unsigned long flags;
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800671
Paul E. McKenney1217ed12011-05-04 21:43:49 -0700672 raw_spin_lock_irqsave(&rnp->lock, flags);
Paul E. McKenney6303b9c2013-12-11 13:59:10 -0800673 smp_mb__after_unlock_lock();
Paul E. McKenney8eb74b22015-02-13 10:52:28 -0800674 if (!rnp->expmask) {
675 /* Phase 1 didn't do anything, so Phase 2 doesn't either. */
Paul E. McKenney1217ed12011-05-04 21:43:49 -0700676 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenney8eb74b22015-02-13 10:52:28 -0800677 return;
678 }
679
680 /* Phase 1 is over. */
681 rnp->expmask = 0;
682
683 /*
684 * If there are still blocked tasks, set up ->exp_tasks so that
685 * rcu_read_unlock_special() will wake us and then boost them.
686 */
687 if (rcu_preempt_has_tasks(rnp)) {
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800688 rnp->exp_tasks = rnp->blkd_tasks.next;
Paul E. McKenney1217ed12011-05-04 21:43:49 -0700689 rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
Paul E. McKenney8eb74b22015-02-13 10:52:28 -0800690 return;
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800691 }
Paul E. McKenney8eb74b22015-02-13 10:52:28 -0800692
693 /* No longer any blocked tasks, so undo bit setting. */
694 raw_spin_unlock_irqrestore(&rnp->lock, flags);
695 rcu_report_exp_rnp(rsp, rnp, false);
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800696}
697
Paul E. McKenney236fefa2012-01-31 14:00:41 -0800698/**
699 * synchronize_rcu_expedited - Brute-force RCU grace period
700 *
701 * Wait for an RCU-preempt grace period, but expedite it. The basic
702 * idea is to invoke synchronize_sched_expedited() to push all the tasks to
703 * the ->blkd_tasks lists and wait for this list to drain. This consumes
704 * significant time on all CPUs and is unfriendly to real-time workloads,
705 * so is thus not recommended for any sort of common-case code.
706 * In fact, if you are using synchronize_rcu_expedited() in a loop,
707 * please restructure your code to batch your updates, and then Use a
708 * single synchronize_rcu() instead.
Paul E. McKenney019129d52009-10-14 10:15:56 -0700709 */
710void synchronize_rcu_expedited(void)
711{
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800712 struct rcu_node *rnp;
713 struct rcu_state *rsp = &rcu_preempt_state;
Paul E. McKenneybcfa57c2012-07-23 16:03:51 -0700714 unsigned long snap;
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800715 int trycount = 0;
716
717 smp_mb(); /* Caller's modifications seen first by other CPUs. */
718 snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
719 smp_mb(); /* Above access cannot bleed into critical section. */
720
721 /*
Paul E. McKenney1943c892012-07-30 17:19:25 -0700722 * Block CPU-hotplug operations. This means that any CPU-hotplug
723 * operation that finds an rcu_node structure with tasks in the
724 * process of being boosted will know that all tasks blocking
725 * this expedited grace period will already be in the process of
726 * being boosted. This simplifies the process of moving tasks
727 * from leaf to root rcu_node structures.
728 */
Paul E. McKenneydd56af42014-08-25 20:25:06 -0700729 if (!try_get_online_cpus()) {
730 /* CPU-hotplug operation in flight, fall back to normal GP. */
731 wait_rcu_gp(call_rcu);
732 return;
733 }
Paul E. McKenney1943c892012-07-30 17:19:25 -0700734
735 /*
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800736 * Acquire lock, falling back to synchronize_rcu() if too many
737 * lock-acquisition failures. Of course, if someone does the
738 * expedited grace period for us, just leave.
739 */
740 while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
Paul E. McKenney1943c892012-07-30 17:19:25 -0700741 if (ULONG_CMP_LT(snap,
742 ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
743 put_online_cpus();
744 goto mb_ret; /* Others did our work for us. */
745 }
Paul E. McKenneyc701d5d2012-06-28 08:08:25 -0700746 if (trycount++ < 10) {
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800747 udelay(trycount * num_online_cpus());
Paul E. McKenneyc701d5d2012-06-28 08:08:25 -0700748 } else {
Paul E. McKenney1943c892012-07-30 17:19:25 -0700749 put_online_cpus();
Antti P Miettinen3705b882012-10-05 09:59:15 +0300750 wait_rcu_gp(call_rcu);
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800751 return;
752 }
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800753 }
Paul E. McKenney1943c892012-07-30 17:19:25 -0700754 if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
755 put_online_cpus();
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800756 goto unlock_mb_ret; /* Others did our work for us. */
Paul E. McKenney1943c892012-07-30 17:19:25 -0700757 }
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800758
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800759 /* force all RCU readers onto ->blkd_tasks lists. */
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800760 synchronize_sched_expedited();
761
Paul E. McKenney8eb74b22015-02-13 10:52:28 -0800762 /*
763 * Snapshot current state of ->blkd_tasks lists into ->expmask.
764 * Phase 1 sets bits and phase 2 permits rcu_read_unlock_special()
765 * to start clearing them. Doing this in one phase leads to
766 * strange races between setting and clearing bits, so just say "no"!
767 */
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800768 rcu_for_each_leaf_node(rsp, rnp)
Paul E. McKenney8eb74b22015-02-13 10:52:28 -0800769 sync_rcu_preempt_exp_init1(rsp, rnp);
770 rcu_for_each_leaf_node(rsp, rnp)
771 sync_rcu_preempt_exp_init2(rsp, rnp);
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800772
Paul E. McKenney1943c892012-07-30 17:19:25 -0700773 put_online_cpus();
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800774
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800775 /* Wait for snapshotted ->blkd_tasks lists to drain. */
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800776 rnp = rcu_get_root(rsp);
777 wait_event(sync_rcu_preempt_exp_wq,
778 sync_rcu_preempt_exp_done(rnp));
779
780 /* Clean up and exit. */
781 smp_mb(); /* ensure expedited GP seen before counter increment. */
Pranith Kumar4de376a2014-07-08 17:46:50 -0400782 ACCESS_ONCE(sync_rcu_preempt_exp_count) =
783 sync_rcu_preempt_exp_count + 1;
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800784unlock_mb_ret:
785 mutex_unlock(&sync_rcu_preempt_exp_mutex);
786mb_ret:
787 smp_mb(); /* ensure subsequent action seen after grace period. */
Paul E. McKenney019129d52009-10-14 10:15:56 -0700788}
789EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
790
Paul E. McKenneye74f4c42009-10-06 21:48:17 -0700791/**
792 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
Paul E. McKenneyf0a0e6f2012-10-23 13:47:01 -0700793 *
794 * Note that this primitive does not necessarily wait for an RCU grace period
795 * to complete. For example, if there are no RCU callbacks queued anywhere
796 * in the system, then rcu_barrier() is within its rights to return
797 * immediately, without waiting for anything, much less an RCU grace period.
Paul E. McKenneye74f4c42009-10-06 21:48:17 -0700798 */
799void rcu_barrier(void)
800{
Paul E. McKenney037b64e2012-05-28 23:26:01 -0700801 _rcu_barrier(&rcu_preempt_state);
Paul E. McKenneye74f4c42009-10-06 21:48:17 -0700802}
803EXPORT_SYMBOL_GPL(rcu_barrier);
804
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700805/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800806 * Initialize preemptible RCU's state structures.
Paul E. McKenney1eba8f82009-09-23 09:50:42 -0700807 */
808static void __init __rcu_init_preempt(void)
809{
Lai Jiangshan394f99a2010-06-28 16:25:04 +0800810 rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
Paul E. McKenney1eba8f82009-09-23 09:50:42 -0700811}
812
Paul E. McKenney2439b692013-04-11 10:15:52 -0700813/*
814 * Check for a task exiting while in a preemptible-RCU read-side
815 * critical section, clean up if so. No need to issue warnings,
816 * as debug_check_no_locks_held() already does this if lockdep
817 * is enabled.
818 */
819void exit_rcu(void)
820{
821 struct task_struct *t = current;
822
823 if (likely(list_empty(&current->rcu_node_entry)))
824 return;
825 t->rcu_read_lock_nesting = 1;
826 barrier();
Paul E. McKenney1d082fd2014-08-14 16:01:53 -0700827 t->rcu_read_unlock_special.b.blocked = true;
Paul E. McKenney2439b692013-04-11 10:15:52 -0700828 __rcu_read_unlock();
829}
830
Pranith Kumar28f65692014-09-22 14:00:48 -0400831#else /* #ifdef CONFIG_PREEMPT_RCU */
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700832
Uma Sharmae5341652014-03-23 22:32:09 -0700833static struct rcu_state *rcu_state_p = &rcu_sched_state;
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800834
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700835/*
836 * Tell them what RCU they are running.
837 */
Paul E. McKenney0e0fc1c2009-11-11 11:28:06 -0800838static void __init rcu_bootup_announce(void)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700839{
Paul E. McKenneyefc151c2013-03-18 16:24:11 -0700840 pr_info("Hierarchical RCU implementation.\n");
Paul E. McKenney26845c22010-04-13 14:19:23 -0700841 rcu_bootup_announce_oddness();
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700842}
843
844/*
Paul E. McKenneycba6d0d2012-07-02 07:08:42 -0700845 * Because preemptible RCU does not exist, we never have to check for
846 * CPUs being in quiescent states.
847 */
Paul E. McKenney38200cf2014-10-21 12:50:04 -0700848static void rcu_preempt_note_context_switch(void)
Paul E. McKenneycba6d0d2012-07-02 07:08:42 -0700849{
850}
851
852/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800853 * Because preemptible RCU does not exist, there are never any preempted
Paul E. McKenneyfc2219d2009-09-23 09:50:41 -0700854 * RCU readers.
855 */
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800856static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
Paul E. McKenneyfc2219d2009-09-23 09:50:41 -0700857{
858 return 0;
859}
860
Paul E. McKenney8af3a5e2014-10-31 11:22:37 -0700861/*
862 * Because there is no preemptible RCU, there can be no readers blocked.
863 */
864static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800865{
Paul E. McKenney8af3a5e2014-10-31 11:22:37 -0700866 return false;
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800867}
868
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700869/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800870 * Because preemptible RCU does not exist, we never have to check for
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700871 * tasks blocked within RCU read-side critical sections.
872 */
Paul E. McKenney1ed509a2010-02-22 17:05:05 -0800873static void rcu_print_detail_task_stall(struct rcu_state *rsp)
874{
875}
876
877/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800878 * Because preemptible RCU does not exist, we never have to check for
Paul E. McKenney1ed509a2010-02-22 17:05:05 -0800879 * tasks blocked within RCU read-side critical sections.
880 */
Paul E. McKenney9bc8b552011-08-13 13:31:47 -0700881static int rcu_print_task_stall(struct rcu_node *rnp)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700882{
Paul E. McKenney9bc8b552011-08-13 13:31:47 -0700883 return 0;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700884}
885
Paul E. McKenney53d84e02010-08-10 14:28:53 -0700886/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800887 * Because there is no preemptible RCU, there can be no readers blocked,
Paul E. McKenney49e29122009-09-18 09:50:19 -0700888 * so there is no need to check for blocked tasks. So check only for
889 * bogus qsmask values.
Paul E. McKenneyb0e165c2009-09-13 09:15:09 -0700890 */
891static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
892{
Paul E. McKenney49e29122009-09-18 09:50:19 -0700893 WARN_ON_ONCE(rnp->qsmask);
Paul E. McKenneyb0e165c2009-09-13 09:15:09 -0700894}
895
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700896/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800897 * Because preemptible RCU does not exist, it never has any callbacks
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700898 * to check.
899 */
Paul E. McKenney86aea0e2014-10-21 08:12:00 -0700900static void rcu_preempt_check_callbacks(void)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700901{
902}
903
904/*
Paul E. McKenney019129d52009-10-14 10:15:56 -0700905 * Wait for an rcu-preempt grace period, but make it happen quickly.
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800906 * But because preemptible RCU does not exist, map to rcu-sched.
Paul E. McKenney019129d52009-10-14 10:15:56 -0700907 */
908void synchronize_rcu_expedited(void)
909{
910 synchronize_sched_expedited();
911}
912EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
913
914/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800915 * Because preemptible RCU does not exist, rcu_barrier() is just
Paul E. McKenneye74f4c42009-10-06 21:48:17 -0700916 * another name for rcu_barrier_sched().
917 */
918void rcu_barrier(void)
919{
920 rcu_barrier_sched();
921}
922EXPORT_SYMBOL_GPL(rcu_barrier);
923
924/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800925 * Because preemptible RCU does not exist, it need not be initialized.
Paul E. McKenney1eba8f82009-09-23 09:50:42 -0700926 */
927static void __init __rcu_init_preempt(void)
928{
929}
930
Paul E. McKenney2439b692013-04-11 10:15:52 -0700931/*
932 * Because preemptible RCU does not exist, tasks cannot possibly exit
933 * while in preemptible RCU read-side critical sections.
934 */
935void exit_rcu(void)
936{
937}
938
Pranith Kumar28f65692014-09-22 14:00:48 -0400939#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
Paul E. McKenney8bd93a22010-02-22 17:04:59 -0800940
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800941#ifdef CONFIG_RCU_BOOST
942
Peter Zijlstra1696a8b2013-10-31 18:18:19 +0100943#include "../locking/rtmutex_common.h"
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800944
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -0800945#ifdef CONFIG_RCU_TRACE
946
947static void rcu_initiate_boost_trace(struct rcu_node *rnp)
948{
Paul E. McKenney96e92022014-10-31 14:09:23 -0700949 if (!rcu_preempt_has_tasks(rnp))
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -0800950 rnp->n_balk_blkd_tasks++;
951 else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
952 rnp->n_balk_exp_gp_tasks++;
953 else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL)
954 rnp->n_balk_boost_tasks++;
955 else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
956 rnp->n_balk_notblocked++;
957 else if (rnp->gp_tasks != NULL &&
Paul E. McKenneya9f47932011-05-02 03:46:10 -0700958 ULONG_CMP_LT(jiffies, rnp->boost_time))
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -0800959 rnp->n_balk_notyet++;
960 else
961 rnp->n_balk_nos++;
962}
963
964#else /* #ifdef CONFIG_RCU_TRACE */
965
966static void rcu_initiate_boost_trace(struct rcu_node *rnp)
967{
968}
969
970#endif /* #else #ifdef CONFIG_RCU_TRACE */
971
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +0000972static void rcu_wake_cond(struct task_struct *t, int status)
973{
974 /*
975 * If the thread is yielding, only wake it when this
976 * is invoked from idle
977 */
978 if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
979 wake_up_process(t);
980}
981
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800982/*
983 * Carry out RCU priority boosting on the task indicated by ->exp_tasks
984 * or ->boost_tasks, advancing the pointer to the next task in the
985 * ->blkd_tasks list.
986 *
987 * Note that irqs must be enabled: boosting the task can block.
988 * Returns 1 if there are more tasks needing to be boosted.
989 */
990static int rcu_boost(struct rcu_node *rnp)
991{
992 unsigned long flags;
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800993 struct task_struct *t;
994 struct list_head *tb;
995
Paul E. McKenneyb08ea272014-10-29 15:39:39 -0700996 if (ACCESS_ONCE(rnp->exp_tasks) == NULL &&
997 ACCESS_ONCE(rnp->boost_tasks) == NULL)
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800998 return 0; /* Nothing left to boost. */
999
1000 raw_spin_lock_irqsave(&rnp->lock, flags);
Paul E. McKenney6303b9c2013-12-11 13:59:10 -08001001 smp_mb__after_unlock_lock();
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001002
1003 /*
1004 * Recheck under the lock: all tasks in need of boosting
1005 * might exit their RCU read-side critical sections on their own.
1006 */
1007 if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
1008 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1009 return 0;
1010 }
1011
1012 /*
1013 * Preferentially boost tasks blocking expedited grace periods.
1014 * This cannot starve the normal grace periods because a second
1015 * expedited grace period must boost all blocked tasks, including
1016 * those blocking the pre-existing normal grace period.
1017 */
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -08001018 if (rnp->exp_tasks != NULL) {
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001019 tb = rnp->exp_tasks;
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -08001020 rnp->n_exp_boosts++;
1021 } else {
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001022 tb = rnp->boost_tasks;
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -08001023 rnp->n_normal_boosts++;
1024 }
1025 rnp->n_tasks_boosted++;
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001026
1027 /*
1028 * We boost task t by manufacturing an rt_mutex that appears to
1029 * be held by task t. We leave a pointer to that rt_mutex where
1030 * task t can find it, and task t will release the mutex when it
1031 * exits its outermost RCU read-side critical section. Then
1032 * simply acquiring this artificial rt_mutex will boost task
1033 * t's priority. (Thanks to tglx for suggesting this approach!)
1034 *
1035 * Note that task t must acquire rnp->lock to remove itself from
1036 * the ->blkd_tasks list, which it will do from exit() if from
1037 * nowhere else. We therefore are guaranteed that task t will
1038 * stay around at least until we drop rnp->lock. Note that
1039 * rnp->lock also resolves races between our priority boosting
1040 * and task t's exiting its outermost RCU read-side critical
1041 * section.
1042 */
1043 t = container_of(tb, struct task_struct, rcu_node_entry);
Paul E. McKenneyabaa93d2014-06-12 13:30:25 -07001044 rt_mutex_init_proxy_locked(&rnp->boost_mtx, t);
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001045 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenneyabaa93d2014-06-12 13:30:25 -07001046 /* Lock only for side effect: boosts task t's priority. */
1047 rt_mutex_lock(&rnp->boost_mtx);
1048 rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001049
Paul E. McKenney4f89b332011-12-09 14:43:47 -08001050 return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
1051 ACCESS_ONCE(rnp->boost_tasks) != NULL;
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001052}
1053
1054/*
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001055 * Priority-boosting kthread. One per leaf rcu_node and one for the
1056 * root rcu_node.
1057 */
1058static int rcu_boost_kthread(void *arg)
1059{
1060 struct rcu_node *rnp = (struct rcu_node *)arg;
1061 int spincnt = 0;
1062 int more2boost;
1063
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04001064 trace_rcu_utilization(TPS("Start boost kthread@init"));
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001065 for (;;) {
Paul E. McKenneyd71df902011-03-29 17:48:28 -07001066 rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04001067 trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
Peter Zijlstra08bca602011-05-20 16:06:29 -07001068 rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04001069 trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
Paul E. McKenneyd71df902011-03-29 17:48:28 -07001070 rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001071 more2boost = rcu_boost(rnp);
1072 if (more2boost)
1073 spincnt++;
1074 else
1075 spincnt = 0;
1076 if (spincnt > 10) {
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001077 rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04001078 trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001079 schedule_timeout_interruptible(2);
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04001080 trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001081 spincnt = 0;
1082 }
1083 }
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001084 /* NOTREACHED */
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04001085 trace_rcu_utilization(TPS("End boost kthread@notreached"));
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001086 return 0;
1087}
1088
1089/*
1090 * Check to see if it is time to start boosting RCU readers that are
1091 * blocking the current grace period, and, if so, tell the per-rcu_node
1092 * kthread to start boosting them. If there is an expedited grace
1093 * period in progress, it is always time to boost.
1094 *
Paul E. McKenneyb065a852012-08-01 15:57:54 -07001095 * The caller must hold rnp->lock, which this function releases.
1096 * The ->boost_kthread_task is immortal, so we don't need to worry
1097 * about it going away.
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001098 */
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001099static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
Pranith Kumar615e41c2014-06-11 16:39:40 -04001100 __releases(rnp->lock)
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001101{
1102 struct task_struct *t;
1103
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -08001104 if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
1105 rnp->n_balk_exp_gp_tasks++;
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001106 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001107 return;
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -08001108 }
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001109 if (rnp->exp_tasks != NULL ||
1110 (rnp->gp_tasks != NULL &&
1111 rnp->boost_tasks == NULL &&
1112 rnp->qsmask == 0 &&
1113 ULONG_CMP_GE(jiffies, rnp->boost_time))) {
1114 if (rnp->exp_tasks == NULL)
1115 rnp->boost_tasks = rnp->gp_tasks;
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001116 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001117 t = rnp->boost_kthread_task;
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001118 if (t)
1119 rcu_wake_cond(t, rnp->boost_kthread_status);
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001120 } else {
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -08001121 rcu_initiate_boost_trace(rnp);
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001122 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1123 }
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001124}
1125
Paul E. McKenney0f962a52011-04-14 12:13:53 -07001126/*
Paul E. McKenneya46e0892011-06-15 15:47:09 -07001127 * Wake up the per-CPU kthread to invoke RCU callbacks.
1128 */
1129static void invoke_rcu_callbacks_kthread(void)
1130{
1131 unsigned long flags;
1132
1133 local_irq_save(flags);
1134 __this_cpu_write(rcu_cpu_has_work, 1);
Shaohua Li1eb52122011-06-16 16:02:54 -07001135 if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001136 current != __this_cpu_read(rcu_cpu_kthread_task)) {
1137 rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
1138 __this_cpu_read(rcu_cpu_kthread_status));
1139 }
Paul E. McKenneya46e0892011-06-15 15:47:09 -07001140 local_irq_restore(flags);
1141}
1142
1143/*
Paul E. McKenneydff16722011-11-29 15:57:13 -08001144 * Is the current CPU running the RCU-callbacks kthread?
1145 * Caller must have preemption disabled.
1146 */
1147static bool rcu_is_callbacks_kthread(void)
1148{
Christoph Lameterc9d4b0a2013-08-31 13:34:10 -07001149 return __this_cpu_read(rcu_cpu_kthread_task) == current;
Paul E. McKenneydff16722011-11-29 15:57:13 -08001150}
1151
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001152#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1153
1154/*
1155 * Do priority-boost accounting for the start of a new grace period.
1156 */
1157static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1158{
1159 rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
1160}
1161
1162/*
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001163 * Create an RCU-boost kthread for the specified node if one does not
1164 * already exist. We only create this kthread for preemptible RCU.
1165 * Returns zero if all is well, a negated errno otherwise.
1166 */
Paul Gortmaker49fb4c62013-06-19 14:52:21 -04001167static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
Paul E. McKenney0aa04b02015-01-23 21:52:37 -08001168 struct rcu_node *rnp)
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001169{
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001170 int rnp_index = rnp - &rsp->node[0];
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001171 unsigned long flags;
1172 struct sched_param sp;
1173 struct task_struct *t;
1174
1175 if (&rcu_preempt_state != rsp)
1176 return 0;
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001177
Paul E. McKenney0aa04b02015-01-23 21:52:37 -08001178 if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0)
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001179 return 0;
1180
Paul E. McKenneya46e0892011-06-15 15:47:09 -07001181 rsp->boost = 1;
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001182 if (rnp->boost_kthread_task != NULL)
1183 return 0;
1184 t = kthread_create(rcu_boost_kthread, (void *)rnp,
Mike Galbraith5b61b0b2011-08-19 11:39:11 -07001185 "rcub/%d", rnp_index);
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001186 if (IS_ERR(t))
1187 return PTR_ERR(t);
1188 raw_spin_lock_irqsave(&rnp->lock, flags);
Paul E. McKenney6303b9c2013-12-11 13:59:10 -08001189 smp_mb__after_unlock_lock();
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001190 rnp->boost_kthread_task = t;
1191 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Clark Williams21871d72014-09-12 21:21:09 -05001192 sp.sched_priority = kthread_prio;
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001193 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
Paul E. McKenney9a432732011-05-30 20:38:55 -07001194 wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001195 return 0;
1196}
1197
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001198static void rcu_kthread_do_work(void)
1199{
Christoph Lameterc9d4b0a2013-08-31 13:34:10 -07001200 rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data));
1201 rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data));
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001202 rcu_preempt_do_callbacks();
1203}
1204
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001205static void rcu_cpu_kthread_setup(unsigned int cpu)
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001206{
1207 struct sched_param sp;
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001208
Clark Williams21871d72014-09-12 21:21:09 -05001209 sp.sched_priority = kthread_prio;
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001210 sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001211}
1212
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001213static void rcu_cpu_kthread_park(unsigned int cpu)
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001214{
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001215 per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
1216}
1217
1218static int rcu_cpu_kthread_should_run(unsigned int cpu)
1219{
Christoph Lameterc9d4b0a2013-08-31 13:34:10 -07001220 return __this_cpu_read(rcu_cpu_has_work);
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001221}
1222
1223/*
1224 * Per-CPU kernel thread that invokes RCU callbacks. This replaces the
Paul E. McKenneye0f23062011-06-21 01:29:39 -07001225 * RCU softirq used in flavors and configurations of RCU that do not
1226 * support RCU priority boosting.
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001227 */
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001228static void rcu_cpu_kthread(unsigned int cpu)
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001229{
Christoph Lameterc9d4b0a2013-08-31 13:34:10 -07001230 unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
1231 char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001232 int spincnt;
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001233
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001234 for (spincnt = 0; spincnt < 10; spincnt++) {
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04001235 trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001236 local_bh_disable();
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001237 *statusp = RCU_KTHREAD_RUNNING;
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001238 this_cpu_inc(rcu_cpu_kthread_loops);
1239 local_irq_disable();
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001240 work = *workp;
1241 *workp = 0;
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001242 local_irq_enable();
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001243 if (work)
1244 rcu_kthread_do_work();
1245 local_bh_enable();
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001246 if (*workp == 0) {
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04001247 trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001248 *statusp = RCU_KTHREAD_WAITING;
1249 return;
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001250 }
1251 }
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001252 *statusp = RCU_KTHREAD_YIELDING;
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04001253 trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001254 schedule_timeout_interruptible(2);
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04001255 trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001256 *statusp = RCU_KTHREAD_WAITING;
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001257}
1258
1259/*
1260 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1261 * served by the rcu_node in question. The CPU hotplug lock is still
1262 * held, so the value of rnp->qsmaskinit will be stable.
1263 *
1264 * We don't include outgoingcpu in the affinity set, use -1 if there is
1265 * no outgoing CPU. If there are no CPUs left in the affinity set,
1266 * this function allows the kthread to execute on any CPU.
1267 */
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001268static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001269{
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001270 struct task_struct *t = rnp->boost_kthread_task;
Paul E. McKenney0aa04b02015-01-23 21:52:37 -08001271 unsigned long mask = rcu_rnp_online_cpus(rnp);
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001272 cpumask_var_t cm;
1273 int cpu;
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001274
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001275 if (!t)
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001276 return;
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001277 if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001278 return;
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001279 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
1280 if ((mask & 0x1) && cpu != outgoingcpu)
1281 cpumask_set_cpu(cpu, cm);
Paul E. McKenney5d0b0242014-11-10 08:07:08 -08001282 if (cpumask_weight(cm) == 0)
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001283 cpumask_setall(cm);
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001284 set_cpus_allowed_ptr(t, cm);
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001285 free_cpumask_var(cm);
1286}
1287
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001288static struct smp_hotplug_thread rcu_cpu_thread_spec = {
1289 .store = &rcu_cpu_kthread_task,
1290 .thread_should_run = rcu_cpu_kthread_should_run,
1291 .thread_fn = rcu_cpu_kthread,
1292 .thread_comm = "rcuc/%u",
1293 .setup = rcu_cpu_kthread_setup,
1294 .park = rcu_cpu_kthread_park,
1295};
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001296
1297/*
Paul E. McKenney9386c0b2014-07-13 12:00:53 -07001298 * Spawn boost kthreads -- called as soon as the scheduler is running.
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001299 */
Paul E. McKenney9386c0b2014-07-13 12:00:53 -07001300static void __init rcu_spawn_boost_kthreads(void)
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001301{
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001302 struct rcu_node *rnp;
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001303 int cpu;
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001304
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001305 for_each_possible_cpu(cpu)
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001306 per_cpu(rcu_cpu_has_work, cpu) = 0;
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001307 BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
Paul E. McKenney3e9f5c72014-11-03 18:15:17 -08001308 rcu_for_each_leaf_node(rcu_state_p, rnp)
1309 (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001310}
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001311
Paul Gortmaker49fb4c62013-06-19 14:52:21 -04001312static void rcu_prepare_kthreads(int cpu)
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001313{
Uma Sharmae5341652014-03-23 22:32:09 -07001314 struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001315 struct rcu_node *rnp = rdp->mynode;
1316
1317 /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001318 if (rcu_scheduler_fully_active)
Uma Sharmae5341652014-03-23 22:32:09 -07001319 (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001320}
1321
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001322#else /* #ifdef CONFIG_RCU_BOOST */
1323
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001324static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
Pranith Kumar615e41c2014-06-11 16:39:40 -04001325 __releases(rnp->lock)
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001326{
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001327 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001328}
1329
Paul E. McKenneya46e0892011-06-15 15:47:09 -07001330static void invoke_rcu_callbacks_kthread(void)
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001331{
Paul E. McKenneya46e0892011-06-15 15:47:09 -07001332 WARN_ON_ONCE(1);
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001333}
1334
Paul E. McKenneydff16722011-11-29 15:57:13 -08001335static bool rcu_is_callbacks_kthread(void)
1336{
1337 return false;
1338}
1339
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001340static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1341{
1342}
1343
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001344static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001345{
1346}
1347
Paul E. McKenney9386c0b2014-07-13 12:00:53 -07001348static void __init rcu_spawn_boost_kthreads(void)
Paul E. McKenneyb0d30412011-07-10 15:57:35 -07001349{
Paul E. McKenneyb0d30412011-07-10 15:57:35 -07001350}
Paul E. McKenneyb0d30412011-07-10 15:57:35 -07001351
Paul Gortmaker49fb4c62013-06-19 14:52:21 -04001352static void rcu_prepare_kthreads(int cpu)
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001353{
1354}
1355
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001356#endif /* #else #ifdef CONFIG_RCU_BOOST */
1357
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001358#if !defined(CONFIG_RCU_FAST_NO_HZ)
1359
1360/*
1361 * Check to see if any future RCU-related work will need to be done
1362 * by the current CPU, even if none need be done immediately, returning
1363 * 1 if so. This function is part of the RCU implementation; it is -not-
1364 * an exported member of the RCU API.
1365 *
Paul E. McKenney7cb92492011-11-28 12:28:34 -08001366 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
1367 * any flavor of RCU.
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001368 */
Paul E. McKenneyffa83fb2013-11-17 19:27:16 -08001369#ifndef CONFIG_RCU_NOCB_CPU_ALL
Paul E. McKenneyaa6da512014-10-21 13:23:08 -07001370int rcu_needs_cpu(unsigned long *delta_jiffies)
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001371{
Paul E. McKenneyaa9b16302012-05-10 16:41:44 -07001372 *delta_jiffies = ULONG_MAX;
Paul E. McKenneyaa6da512014-10-21 13:23:08 -07001373 return rcu_cpu_has_callbacks(NULL);
Paul E. McKenney7cb92492011-11-28 12:28:34 -08001374}
Paul E. McKenneyffa83fb2013-11-17 19:27:16 -08001375#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
Paul E. McKenney7cb92492011-11-28 12:28:34 -08001376
1377/*
1378 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
1379 * after it.
1380 */
Paul E. McKenney8fa7845d2014-10-22 15:07:37 -07001381static void rcu_cleanup_after_idle(void)
Paul E. McKenney7cb92492011-11-28 12:28:34 -08001382{
1383}
1384
1385/*
Paul E. McKenneya858af22012-01-16 13:29:10 -08001386 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
Paul E. McKenneyaea1b352011-11-02 06:54:54 -07001387 * is nothing.
1388 */
Paul E. McKenney198bbf82014-10-22 15:03:43 -07001389static void rcu_prepare_for_idle(void)
Paul E. McKenneyaea1b352011-11-02 06:54:54 -07001390{
1391}
1392
Paul E. McKenneyc57afe82012-02-28 11:02:21 -08001393/*
1394 * Don't bother keeping a running count of the number of RCU callbacks
1395 * posted because CONFIG_RCU_FAST_NO_HZ=n.
1396 */
1397static void rcu_idle_count_callbacks_posted(void)
1398{
1399}
1400
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001401#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1402
Paul E. McKenneyf23f7fa2011-11-30 15:41:14 -08001403/*
1404 * This code is invoked when a CPU goes idle, at which point we want
1405 * to have the CPU do everything required for RCU so that it can enter
1406 * the energy-efficient dyntick-idle mode. This is handled by a
1407 * state machine implemented by rcu_prepare_for_idle() below.
1408 *
1409 * The following three proprocessor symbols control this state machine:
1410 *
Paul E. McKenneyf23f7fa2011-11-30 15:41:14 -08001411 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
1412 * to sleep in dyntick-idle mode with RCU callbacks pending. This
1413 * is sized to be roughly one RCU grace period. Those energy-efficiency
1414 * benchmarkers who might otherwise be tempted to set this to a large
1415 * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
1416 * system. And if you are -that- concerned about energy efficiency,
1417 * just power the system down and be done with it!
Paul E. McKenney778d2502012-01-10 14:13:24 -08001418 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
1419 * permitted to sleep in dyntick-idle mode with only lazy RCU
1420 * callbacks pending. Setting this too high can OOM your system.
Paul E. McKenneyf23f7fa2011-11-30 15:41:14 -08001421 *
1422 * The values below work well in practice. If future workloads require
1423 * adjustment, they can be converted into kernel config parameters, though
1424 * making the state machine smarter might be a better option.
1425 */
Paul E. McKenneye84c48a2012-06-04 20:45:10 -07001426#define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
Paul E. McKenney778d2502012-01-10 14:13:24 -08001427#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
Paul E. McKenneyf23f7fa2011-11-30 15:41:14 -08001428
Paul E. McKenney5e44ce32012-12-12 12:35:29 -08001429static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
1430module_param(rcu_idle_gp_delay, int, 0644);
1431static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
1432module_param(rcu_idle_lazy_gp_delay, int, 0644);
1433
Thomas Gleixnerd689fe22013-11-13 21:01:57 +01001434extern int tick_nohz_active;
Paul E. McKenney9d2ad242012-06-24 10:15:02 -07001435
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001436/*
Paul E. McKenneyc2298282013-08-25 21:20:47 -07001437 * Try to advance callbacks for all flavors of RCU on the current CPU, but
1438 * only if it has been awhile since the last time we did so. Afterwards,
1439 * if there are any callbacks ready for immediate invocation, return true.
Paul E. McKenney486e2592012-01-06 14:11:30 -08001440 */
Paul E. McKenneyf1f399d2013-11-17 21:08:07 -08001441static bool __maybe_unused rcu_try_advance_all_cbs(void)
Paul E. McKenney486e2592012-01-06 14:11:30 -08001442{
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001443 bool cbs_ready = false;
1444 struct rcu_data *rdp;
Paul E. McKenneyc2298282013-08-25 21:20:47 -07001445 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001446 struct rcu_node *rnp;
1447 struct rcu_state *rsp;
Paul E. McKenney486e2592012-01-06 14:11:30 -08001448
Paul E. McKenneyc2298282013-08-25 21:20:47 -07001449 /* Exit early if we advanced recently. */
1450 if (jiffies == rdtp->last_advance_all)
Pranith Kumard0bc90f2014-07-08 18:26:13 -04001451 return false;
Paul E. McKenneyc2298282013-08-25 21:20:47 -07001452 rdtp->last_advance_all = jiffies;
1453
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001454 for_each_rcu_flavor(rsp) {
1455 rdp = this_cpu_ptr(rsp->rda);
1456 rnp = rdp->mynode;
Paul E. McKenney486e2592012-01-06 14:11:30 -08001457
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001458 /*
1459 * Don't bother checking unless a grace period has
1460 * completed since we last checked and there are
1461 * callbacks not yet ready to invoke.
1462 */
Paul E. McKenneye3663b12014-12-08 20:26:55 -08001463 if ((rdp->completed != rnp->completed ||
1464 unlikely(ACCESS_ONCE(rdp->gpwrap))) &&
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001465 rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL])
Paul E. McKenney470716f2013-03-19 11:32:11 -07001466 note_gp_changes(rsp, rdp);
Paul E. McKenney486e2592012-01-06 14:11:30 -08001467
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001468 if (cpu_has_callbacks_ready_to_invoke(rdp))
1469 cbs_ready = true;
1470 }
1471 return cbs_ready;
Paul E. McKenney486e2592012-01-06 14:11:30 -08001472}
1473
1474/*
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001475 * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
1476 * to invoke. If the CPU has callbacks, try to advance them. Tell the
1477 * caller to set the timeout based on whether or not there are non-lazy
1478 * callbacks.
Paul E. McKenneyaa9b16302012-05-10 16:41:44 -07001479 *
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001480 * The caller must have disabled interrupts.
Paul E. McKenneyaa9b16302012-05-10 16:41:44 -07001481 */
Paul E. McKenneyffa83fb2013-11-17 19:27:16 -08001482#ifndef CONFIG_RCU_NOCB_CPU_ALL
Paul E. McKenneyaa6da512014-10-21 13:23:08 -07001483int rcu_needs_cpu(unsigned long *dj)
Paul E. McKenneyaa9b16302012-05-10 16:41:44 -07001484{
Paul E. McKenneyaa6da512014-10-21 13:23:08 -07001485 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
Paul E. McKenneyaa9b16302012-05-10 16:41:44 -07001486
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001487 /* Snapshot to detect later posting of non-lazy callback. */
1488 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1489
Paul E. McKenneyaa9b16302012-05-10 16:41:44 -07001490 /* If no callbacks, RCU doesn't need the CPU. */
Paul E. McKenneyaa6da512014-10-21 13:23:08 -07001491 if (!rcu_cpu_has_callbacks(&rdtp->all_lazy)) {
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001492 *dj = ULONG_MAX;
Paul E. McKenneyaa9b16302012-05-10 16:41:44 -07001493 return 0;
1494 }
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001495
1496 /* Attempt to advance callbacks. */
1497 if (rcu_try_advance_all_cbs()) {
1498 /* Some ready to invoke, so initiate later invocation. */
1499 invoke_rcu_core();
Paul E. McKenneyaa9b16302012-05-10 16:41:44 -07001500 return 1;
1501 }
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001502 rdtp->last_accelerate = jiffies;
1503
1504 /* Request timer delay depending on laziness, and round. */
Paul E. McKenney6faf7282013-05-13 06:53:37 -07001505 if (!rdtp->all_lazy) {
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001506 *dj = round_up(rcu_idle_gp_delay + jiffies,
1507 rcu_idle_gp_delay) - jiffies;
Paul E. McKenneye84c48a2012-06-04 20:45:10 -07001508 } else {
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001509 *dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
Paul E. McKenneye84c48a2012-06-04 20:45:10 -07001510 }
Paul E. McKenneyaa9b16302012-05-10 16:41:44 -07001511 return 0;
1512}
Paul E. McKenneyffa83fb2013-11-17 19:27:16 -08001513#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
Paul E. McKenneyaa9b16302012-05-10 16:41:44 -07001514
1515/*
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001516 * Prepare a CPU for idle from an RCU perspective. The first major task
1517 * is to sense whether nohz mode has been enabled or disabled via sysfs.
1518 * The second major task is to check to see if a non-lazy callback has
1519 * arrived at a CPU that previously had only lazy callbacks. The third
1520 * major task is to accelerate (that is, assign grace-period numbers to)
1521 * any recently arrived callbacks.
Paul E. McKenneyaea1b352011-11-02 06:54:54 -07001522 *
1523 * The caller must have disabled interrupts.
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001524 */
Paul E. McKenney198bbf82014-10-22 15:03:43 -07001525static void rcu_prepare_for_idle(void)
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001526{
Paul E. McKenneyf1f399d2013-11-17 21:08:07 -08001527#ifndef CONFIG_RCU_NOCB_CPU_ALL
Paul E. McKenney48a76392014-03-11 13:02:16 -07001528 bool needwake;
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001529 struct rcu_data *rdp;
Paul E. McKenney198bbf82014-10-22 15:03:43 -07001530 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001531 struct rcu_node *rnp;
1532 struct rcu_state *rsp;
Paul E. McKenney9d2ad242012-06-24 10:15:02 -07001533 int tne;
1534
1535 /* Handle nohz enablement switches conservatively. */
Thomas Gleixnerd689fe22013-11-13 21:01:57 +01001536 tne = ACCESS_ONCE(tick_nohz_active);
Paul E. McKenney9d2ad242012-06-24 10:15:02 -07001537 if (tne != rdtp->tick_nohz_enabled_snap) {
Paul E. McKenneyaa6da512014-10-21 13:23:08 -07001538 if (rcu_cpu_has_callbacks(NULL))
Paul E. McKenney9d2ad242012-06-24 10:15:02 -07001539 invoke_rcu_core(); /* force nohz to see update. */
1540 rdtp->tick_nohz_enabled_snap = tne;
1541 return;
1542 }
1543 if (!tne)
1544 return;
Paul E. McKenneyf511fc62012-03-15 12:16:26 -07001545
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001546 /* If this is a no-CBs CPU, no callbacks, just return. */
Paul E. McKenney198bbf82014-10-22 15:03:43 -07001547 if (rcu_is_nocb_cpu(smp_processor_id()))
Paul E. McKenney9a0c6fe2012-06-28 12:33:51 -07001548 return;
Paul E. McKenney9a0c6fe2012-06-28 12:33:51 -07001549
Paul E. McKenney3084f2f2011-11-22 17:07:11 -08001550 /*
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001551 * If a non-lazy callback arrived at a CPU having only lazy
1552 * callbacks, invoke RCU core for the side-effect of recalculating
1553 * idle duration on re-entry to idle.
Paul E. McKenneyc57afe82012-02-28 11:02:21 -08001554 */
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001555 if (rdtp->all_lazy &&
1556 rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
Paul E. McKenneyc337f8f2013-09-05 17:02:11 -07001557 rdtp->all_lazy = false;
1558 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
Paul E. McKenneya46e0892011-06-15 15:47:09 -07001559 invoke_rcu_core();
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001560 return;
1561 }
1562
1563 /*
1564 * If we have not yet accelerated this jiffy, accelerate all
1565 * callbacks on this CPU.
1566 */
1567 if (rdtp->last_accelerate == jiffies)
1568 return;
1569 rdtp->last_accelerate = jiffies;
1570 for_each_rcu_flavor(rsp) {
Paul E. McKenney198bbf82014-10-22 15:03:43 -07001571 rdp = this_cpu_ptr(rsp->rda);
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001572 if (!*rdp->nxttail[RCU_DONE_TAIL])
1573 continue;
1574 rnp = rdp->mynode;
1575 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
Paul E. McKenney6303b9c2013-12-11 13:59:10 -08001576 smp_mb__after_unlock_lock();
Paul E. McKenney48a76392014-03-11 13:02:16 -07001577 needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001578 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
Paul E. McKenney48a76392014-03-11 13:02:16 -07001579 if (needwake)
1580 rcu_gp_kthread_wake(rsp);
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001581 }
Paul E. McKenneyf1f399d2013-11-17 21:08:07 -08001582#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001583}
1584
1585/*
1586 * Clean up for exit from idle. Attempt to advance callbacks based on
1587 * any grace periods that elapsed while the CPU was idle, and if any
1588 * callbacks are now ready to invoke, initiate invocation.
1589 */
Paul E. McKenney8fa7845d2014-10-22 15:07:37 -07001590static void rcu_cleanup_after_idle(void)
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001591{
Paul E. McKenneyf1f399d2013-11-17 21:08:07 -08001592#ifndef CONFIG_RCU_NOCB_CPU_ALL
Paul E. McKenney8fa7845d2014-10-22 15:07:37 -07001593 if (rcu_is_nocb_cpu(smp_processor_id()))
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001594 return;
Paul E. McKenney7a497c92013-08-22 18:16:16 -07001595 if (rcu_try_advance_all_cbs())
1596 invoke_rcu_core();
Paul E. McKenneyf1f399d2013-11-17 21:08:07 -08001597#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001598}
1599
Paul E. McKenneyc57afe82012-02-28 11:02:21 -08001600/*
Paul E. McKenney98248a02012-05-03 15:38:10 -07001601 * Keep a running count of the number of non-lazy callbacks posted
1602 * on this CPU. This running counter (which is never decremented) allows
1603 * rcu_prepare_for_idle() to detect when something out of the idle loop
1604 * posts a callback, even if an equal number of callbacks are invoked.
1605 * Of course, callbacks should only be posted from within a trace event
1606 * designed to be called from idle or from within RCU_NONIDLE().
Paul E. McKenneyc57afe82012-02-28 11:02:21 -08001607 */
1608static void rcu_idle_count_callbacks_posted(void)
1609{
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07001610 __this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
Paul E. McKenneyc57afe82012-02-28 11:02:21 -08001611}
1612
Paul E. McKenneyb626c1b2012-06-11 17:39:43 -07001613/*
1614 * Data for flushing lazy RCU callbacks at OOM time.
1615 */
1616static atomic_t oom_callback_count;
1617static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);
1618
1619/*
1620 * RCU OOM callback -- decrement the outstanding count and deliver the
1621 * wake-up if we are the last one.
1622 */
1623static void rcu_oom_callback(struct rcu_head *rhp)
1624{
1625 if (atomic_dec_and_test(&oom_callback_count))
1626 wake_up(&oom_callback_wq);
1627}
1628
1629/*
1630 * Post an rcu_oom_notify callback on the current CPU if it has at
1631 * least one lazy callback. This will unnecessarily post callbacks
1632 * to CPUs that already have a non-lazy callback at the end of their
1633 * callback list, but this is an infrequent operation, so accept some
1634 * extra overhead to keep things simple.
1635 */
1636static void rcu_oom_notify_cpu(void *unused)
1637{
1638 struct rcu_state *rsp;
1639 struct rcu_data *rdp;
1640
1641 for_each_rcu_flavor(rsp) {
Christoph Lameterfa07a582014-04-15 12:20:12 -07001642 rdp = raw_cpu_ptr(rsp->rda);
Paul E. McKenneyb626c1b2012-06-11 17:39:43 -07001643 if (rdp->qlen_lazy != 0) {
1644 atomic_inc(&oom_callback_count);
1645 rsp->call(&rdp->oom_head, rcu_oom_callback);
1646 }
1647 }
1648}
1649
1650/*
1651 * If low on memory, ensure that each CPU has a non-lazy callback.
1652 * This will wake up CPUs that have only lazy callbacks, in turn
1653 * ensuring that they free up the corresponding memory in a timely manner.
1654 * Because an uncertain amount of memory will be freed in some uncertain
1655 * timeframe, we do not claim to have freed anything.
1656 */
1657static int rcu_oom_notify(struct notifier_block *self,
1658 unsigned long notused, void *nfreed)
1659{
1660 int cpu;
1661
1662 /* Wait for callbacks from earlier instance to complete. */
1663 wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);
Paul E. McKenney78e4bc32013-09-24 15:04:06 -07001664 smp_mb(); /* Ensure callback reuse happens after callback invocation. */
Paul E. McKenneyb626c1b2012-06-11 17:39:43 -07001665
1666 /*
1667 * Prevent premature wakeup: ensure that all increments happen
1668 * before there is a chance of the counter reaching zero.
1669 */
1670 atomic_set(&oom_callback_count, 1);
1671
1672 get_online_cpus();
1673 for_each_online_cpu(cpu) {
1674 smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
Paul E. McKenneybde6c3a2014-07-01 11:26:57 -07001675 cond_resched_rcu_qs();
Paul E. McKenneyb626c1b2012-06-11 17:39:43 -07001676 }
1677 put_online_cpus();
1678
1679 /* Unconditionally decrement: no need to wake ourselves up. */
1680 atomic_dec(&oom_callback_count);
1681
1682 return NOTIFY_OK;
1683}
1684
1685static struct notifier_block rcu_oom_nb = {
1686 .notifier_call = rcu_oom_notify
1687};
1688
1689static int __init rcu_register_oom_notifier(void)
1690{
1691 register_oom_notifier(&rcu_oom_nb);
1692 return 0;
1693}
1694early_initcall(rcu_register_oom_notifier);
1695
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001696#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
Paul E. McKenneya858af22012-01-16 13:29:10 -08001697
1698#ifdef CONFIG_RCU_CPU_STALL_INFO
1699
1700#ifdef CONFIG_RCU_FAST_NO_HZ
1701
1702static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
1703{
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07001704 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001705 unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
Paul E. McKenneya858af22012-01-16 13:29:10 -08001706
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001707 sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
1708 rdtp->last_accelerate & 0xffff, jiffies & 0xffff,
1709 ulong2long(nlpd),
1710 rdtp->all_lazy ? 'L' : '.',
1711 rdtp->tick_nohz_enabled_snap ? '.' : 'D');
Paul E. McKenneya858af22012-01-16 13:29:10 -08001712}
1713
1714#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
1715
1716static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
1717{
Carsten Emde1c17e4d2012-06-19 10:43:16 +02001718 *cp = '\0';
Paul E. McKenneya858af22012-01-16 13:29:10 -08001719}
1720
1721#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
1722
1723/* Initiate the stall-info list. */
1724static void print_cpu_stall_info_begin(void)
1725{
Paul E. McKenneyefc151c2013-03-18 16:24:11 -07001726 pr_cont("\n");
Paul E. McKenneya858af22012-01-16 13:29:10 -08001727}
1728
1729/*
1730 * Print out diagnostic information for the specified stalled CPU.
1731 *
1732 * If the specified CPU is aware of the current RCU grace period
1733 * (flavor specified by rsp), then print the number of scheduling
1734 * clock interrupts the CPU has taken during the time that it has
1735 * been aware. Otherwise, print the number of RCU grace periods
1736 * that this CPU is ignorant of, for example, "1" if the CPU was
1737 * aware of the previous grace period.
1738 *
1739 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
1740 */
1741static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
1742{
1743 char fast_no_hz[72];
1744 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1745 struct rcu_dynticks *rdtp = rdp->dynticks;
1746 char *ticks_title;
1747 unsigned long ticks_value;
1748
1749 if (rsp->gpnum == rdp->gpnum) {
1750 ticks_title = "ticks this GP";
1751 ticks_value = rdp->ticks_this_gp;
1752 } else {
1753 ticks_title = "GPs behind";
1754 ticks_value = rsp->gpnum - rdp->gpnum;
1755 }
1756 print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
Paul E. McKenneyfc908ed2014-12-08 09:57:48 -08001757 pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u fqs=%ld %s\n",
Paul E. McKenneya858af22012-01-16 13:29:10 -08001758 cpu, ticks_value, ticks_title,
1759 atomic_read(&rdtp->dynticks) & 0xfff,
1760 rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
Paul E. McKenney62310692013-03-06 13:37:09 -08001761 rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
Paul E. McKenneyfc908ed2014-12-08 09:57:48 -08001762 ACCESS_ONCE(rsp->n_force_qs) - rsp->n_force_qs_gpstart,
Paul E. McKenneya858af22012-01-16 13:29:10 -08001763 fast_no_hz);
1764}
1765
1766/* Terminate the stall-info list. */
1767static void print_cpu_stall_info_end(void)
1768{
Paul E. McKenneyefc151c2013-03-18 16:24:11 -07001769 pr_err("\t");
Paul E. McKenneya858af22012-01-16 13:29:10 -08001770}
1771
1772/* Zero ->ticks_this_gp for all flavors of RCU. */
1773static void zero_cpu_stall_ticks(struct rcu_data *rdp)
1774{
1775 rdp->ticks_this_gp = 0;
Paul E. McKenney62310692013-03-06 13:37:09 -08001776 rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
Paul E. McKenneya858af22012-01-16 13:29:10 -08001777}
1778
1779/* Increment ->ticks_this_gp for all flavors of RCU. */
1780static void increment_cpu_stall_ticks(void)
1781{
Paul E. McKenney115f7a72012-08-10 13:55:03 -07001782 struct rcu_state *rsp;
1783
1784 for_each_rcu_flavor(rsp)
Christoph Lameterfa07a582014-04-15 12:20:12 -07001785 raw_cpu_inc(rsp->rda->ticks_this_gp);
Paul E. McKenneya858af22012-01-16 13:29:10 -08001786}
1787
1788#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
1789
1790static void print_cpu_stall_info_begin(void)
1791{
Paul E. McKenneyefc151c2013-03-18 16:24:11 -07001792 pr_cont(" {");
Paul E. McKenneya858af22012-01-16 13:29:10 -08001793}
1794
1795static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
1796{
Paul E. McKenneyefc151c2013-03-18 16:24:11 -07001797 pr_cont(" %d", cpu);
Paul E. McKenneya858af22012-01-16 13:29:10 -08001798}
1799
1800static void print_cpu_stall_info_end(void)
1801{
Paul E. McKenneyefc151c2013-03-18 16:24:11 -07001802 pr_cont("} ");
Paul E. McKenneya858af22012-01-16 13:29:10 -08001803}
1804
1805static void zero_cpu_stall_ticks(struct rcu_data *rdp)
1806{
1807}
1808
1809static void increment_cpu_stall_ticks(void)
1810{
1811}
1812
1813#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07001814
1815#ifdef CONFIG_RCU_NOCB_CPU
1816
1817/*
1818 * Offload callback processing from the boot-time-specified set of CPUs
1819 * specified by rcu_nocb_mask. For each CPU in the set, there is a
1820 * kthread created that pulls the callbacks from the corresponding CPU,
1821 * waits for a grace period to elapse, and invokes the callbacks.
1822 * The no-CBs CPUs do a wake_up() on their kthread when they insert
1823 * a callback into any empty list, unless the rcu_nocb_poll boot parameter
1824 * has been specified, in which case each kthread actively polls its
1825 * CPU. (Which isn't so great for energy efficiency, but which does
1826 * reduce RCU's overhead on that CPU.)
1827 *
1828 * This is intended to be used in conjunction with Frederic Weisbecker's
1829 * adaptive-idle work, which would seriously reduce OS jitter on CPUs
1830 * running CPU-bound user-mode computations.
1831 *
1832 * Offloading of callback processing could also in theory be used as
1833 * an energy-efficiency measure because CPUs with no RCU callbacks
1834 * queued are more aggressive about entering dyntick-idle mode.
1835 */
1836
1837
1838/* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
1839static int __init rcu_nocb_setup(char *str)
1840{
1841 alloc_bootmem_cpumask_var(&rcu_nocb_mask);
1842 have_rcu_nocb_mask = true;
1843 cpulist_parse(str, rcu_nocb_mask);
1844 return 1;
1845}
1846__setup("rcu_nocbs=", rcu_nocb_setup);
1847
Paul Gortmaker1b0048a2012-12-20 13:19:22 -08001848static int __init parse_rcu_nocb_poll(char *arg)
1849{
1850 rcu_nocb_poll = 1;
1851 return 0;
1852}
1853early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
1854
Paul E. McKenney34ed62462013-01-07 13:37:42 -08001855/*
Paul E. McKenney0446be42012-12-30 15:21:01 -08001856 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
1857 * grace period.
Paul E. McKenneydae6e642013-02-10 20:48:58 -08001858 */
Paul E. McKenney0446be42012-12-30 15:21:01 -08001859static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
Paul E. McKenneydae6e642013-02-10 20:48:58 -08001860{
Paul E. McKenney0446be42012-12-30 15:21:01 -08001861 wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]);
Paul E. McKenneydae6e642013-02-10 20:48:58 -08001862}
1863
1864/*
Paul E. McKenney8b425aa82012-12-30 13:06:35 -08001865 * Set the root rcu_node structure's ->need_future_gp field
Paul E. McKenneydae6e642013-02-10 20:48:58 -08001866 * based on the sum of those of all rcu_node structures. This does
1867 * double-count the root rcu_node structure's requests, but this
1868 * is necessary to handle the possibility of a rcu_nocb_kthread()
1869 * having awakened during the time that the rcu_node structures
1870 * were being updated for the end of the previous grace period.
1871 */
1872static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
1873{
Paul E. McKenney8b425aa82012-12-30 13:06:35 -08001874 rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;
Paul E. McKenneydae6e642013-02-10 20:48:58 -08001875}
1876
1877static void rcu_init_one_nocb(struct rcu_node *rnp)
1878{
1879 init_waitqueue_head(&rnp->nocb_gp_wq[0]);
1880 init_waitqueue_head(&rnp->nocb_gp_wq[1]);
Paul E. McKenney34ed62462013-01-07 13:37:42 -08001881}
1882
Paul E. McKenney2f33b512013-11-17 18:25:48 -08001883#ifndef CONFIG_RCU_NOCB_CPU_ALL
Liu Ping Fan24342c92014-02-24 06:18:09 -08001884/* Is the specified CPU a no-CBs CPU? */
Frederic Weisbeckerd1e43fa2013-03-26 23:47:24 +01001885bool rcu_is_nocb_cpu(int cpu)
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07001886{
1887 if (have_rcu_nocb_mask)
1888 return cpumask_test_cpu(cpu, rcu_nocb_mask);
1889 return false;
1890}
Paul E. McKenney2f33b512013-11-17 18:25:48 -08001891#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07001892
1893/*
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07001894 * Kick the leader kthread for this NOCB group.
1895 */
1896static void wake_nocb_leader(struct rcu_data *rdp, bool force)
1897{
1898 struct rcu_data *rdp_leader = rdp->nocb_leader;
1899
1900 if (!ACCESS_ONCE(rdp_leader->nocb_kthread))
1901 return;
Pranith Kumar11ed7f92014-08-27 16:43:40 -04001902 if (ACCESS_ONCE(rdp_leader->nocb_leader_sleep) || force) {
Paul E. McKenney39953df2014-08-12 10:47:48 -07001903 /* Prior smp_mb__after_atomic() orders against prior enqueue. */
Pranith Kumar11ed7f92014-08-27 16:43:40 -04001904 ACCESS_ONCE(rdp_leader->nocb_leader_sleep) = false;
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07001905 wake_up(&rdp_leader->nocb_wq);
1906 }
1907}
1908
1909/*
Paul E. McKenneyd7e29932014-10-27 09:15:54 -07001910 * Does the specified CPU need an RCU callback for the specified flavor
1911 * of rcu_barrier()?
1912 */
1913static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
1914{
1915 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
Paul E. McKenney41050a02014-12-18 12:31:27 -08001916 unsigned long ret;
1917#ifdef CONFIG_PROVE_RCU
Paul E. McKenneyd7e29932014-10-27 09:15:54 -07001918 struct rcu_head *rhp;
Paul E. McKenney41050a02014-12-18 12:31:27 -08001919#endif /* #ifdef CONFIG_PROVE_RCU */
Paul E. McKenneyd7e29932014-10-27 09:15:54 -07001920
Paul E. McKenney41050a02014-12-18 12:31:27 -08001921 /*
1922 * Check count of all no-CBs callbacks awaiting invocation.
1923 * There needs to be a barrier before this function is called,
1924 * but associated with a prior determination that no more
1925 * callbacks would be posted. In the worst case, the first
1926 * barrier in _rcu_barrier() suffices (but the caller cannot
1927 * necessarily rely on this, not a substitute for the caller
1928 * getting the concurrency design right!). There must also be
1929 * a barrier between the following load an posting of a callback
1930 * (if a callback is in fact needed). This is associated with an
1931 * atomic_inc() in the caller.
1932 */
1933 ret = atomic_long_read(&rdp->nocb_q_count);
1934
1935#ifdef CONFIG_PROVE_RCU
Paul E. McKenneyd7e29932014-10-27 09:15:54 -07001936 rhp = ACCESS_ONCE(rdp->nocb_head);
1937 if (!rhp)
1938 rhp = ACCESS_ONCE(rdp->nocb_gp_head);
1939 if (!rhp)
1940 rhp = ACCESS_ONCE(rdp->nocb_follower_head);
1941
1942 /* Having no rcuo kthread but CBs after scheduler starts is bad! */
1943 if (!ACCESS_ONCE(rdp->nocb_kthread) && rhp) {
1944 /* RCU callback enqueued before CPU first came online??? */
1945 pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n",
1946 cpu, rhp->func);
1947 WARN_ON_ONCE(1);
1948 }
Paul E. McKenney41050a02014-12-18 12:31:27 -08001949#endif /* #ifdef CONFIG_PROVE_RCU */
Paul E. McKenneyd7e29932014-10-27 09:15:54 -07001950
Paul E. McKenney41050a02014-12-18 12:31:27 -08001951 return !!ret;
Paul E. McKenneyd7e29932014-10-27 09:15:54 -07001952}
1953
1954/*
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07001955 * Enqueue the specified string of rcu_head structures onto the specified
1956 * CPU's no-CBs lists. The CPU is specified by rdp, the head of the
1957 * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy
1958 * counts are supplied by rhcount and rhcount_lazy.
1959 *
1960 * If warranted, also wake up the kthread servicing this CPUs queues.
1961 */
1962static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
1963 struct rcu_head *rhp,
1964 struct rcu_head **rhtp,
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07001965 int rhcount, int rhcount_lazy,
1966 unsigned long flags)
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07001967{
1968 int len;
1969 struct rcu_head **old_rhpp;
1970 struct task_struct *t;
1971
1972 /* Enqueue the callback on the nocb list and update counts. */
Paul E. McKenney41050a02014-12-18 12:31:27 -08001973 atomic_long_add(rhcount, &rdp->nocb_q_count);
1974 /* rcu_barrier() relies on ->nocb_q_count add before xchg. */
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07001975 old_rhpp = xchg(&rdp->nocb_tail, rhtp);
1976 ACCESS_ONCE(*old_rhpp) = rhp;
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07001977 atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
Paul E. McKenney39953df2014-08-12 10:47:48 -07001978 smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07001979
1980 /* If we are not being polled and there is a kthread, awaken it ... */
1981 t = ACCESS_ONCE(rdp->nocb_kthread);
Paul E. McKenney25e03a72013-10-15 12:47:04 -07001982 if (rcu_nocb_poll || !t) {
Paul E. McKenney9261dd02013-08-14 16:24:26 -07001983 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
1984 TPS("WakeNotPoll"));
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07001985 return;
Paul E. McKenney9261dd02013-08-14 16:24:26 -07001986 }
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07001987 len = atomic_long_read(&rdp->nocb_q_count);
1988 if (old_rhpp == &rdp->nocb_head) {
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07001989 if (!irqs_disabled_flags(flags)) {
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07001990 /* ... if queue was empty ... */
1991 wake_nocb_leader(rdp, false);
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07001992 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
1993 TPS("WakeEmpty"));
1994 } else {
Paul E. McKenney9fdd3bc2014-07-29 14:50:47 -07001995 rdp->nocb_defer_wakeup = RCU_NOGP_WAKE;
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07001996 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
1997 TPS("WakeEmptyIsDeferred"));
1998 }
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07001999 rdp->qlen_last_fqs_check = 0;
2000 } else if (len > rdp->qlen_last_fqs_check + qhimark) {
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07002001 /* ... or if many callbacks queued. */
Paul E. McKenney9fdd3bc2014-07-29 14:50:47 -07002002 if (!irqs_disabled_flags(flags)) {
2003 wake_nocb_leader(rdp, true);
2004 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2005 TPS("WakeOvf"));
2006 } else {
2007 rdp->nocb_defer_wakeup = RCU_NOGP_WAKE_FORCE;
2008 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2009 TPS("WakeOvfIsDeferred"));
2010 }
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002011 rdp->qlen_last_fqs_check = LONG_MAX / 2;
Paul E. McKenney9261dd02013-08-14 16:24:26 -07002012 } else {
2013 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002014 }
2015 return;
2016}
2017
2018/*
2019 * This is a helper for __call_rcu(), which invokes this when the normal
2020 * callback queue is inoperable. If this is not a no-CBs CPU, this
2021 * function returns failure back to __call_rcu(), which can complain
2022 * appropriately.
2023 *
2024 * Otherwise, this function queues the callback where the corresponding
2025 * "rcuo" kthread can find it.
2026 */
2027static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07002028 bool lazy, unsigned long flags)
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002029{
2030
Frederic Weisbeckerd1e43fa2013-03-26 23:47:24 +01002031 if (!rcu_is_nocb_cpu(rdp->cpu))
Pranith Kumarc271d3a2014-07-08 18:26:14 -04002032 return false;
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07002033 __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags);
Paul E. McKenney21e7a602013-02-09 17:42:16 -08002034 if (__is_kfree_rcu_offset((unsigned long)rhp->func))
2035 trace_rcu_kfree_callback(rdp->rsp->name, rhp,
2036 (unsigned long)rhp->func,
Paul E. McKenney756cbf62013-08-15 10:12:12 -07002037 -atomic_long_read(&rdp->nocb_q_count_lazy),
2038 -atomic_long_read(&rdp->nocb_q_count));
Paul E. McKenney21e7a602013-02-09 17:42:16 -08002039 else
2040 trace_rcu_callback(rdp->rsp->name, rhp,
Paul E. McKenney756cbf62013-08-15 10:12:12 -07002041 -atomic_long_read(&rdp->nocb_q_count_lazy),
2042 -atomic_long_read(&rdp->nocb_q_count));
Paul E. McKenney1772947bd2014-08-12 11:27:31 -07002043
2044 /*
2045 * If called from an extended quiescent state with interrupts
2046 * disabled, invoke the RCU core in order to allow the idle-entry
2047 * deferred-wakeup check to function.
2048 */
2049 if (irqs_disabled_flags(flags) &&
2050 !rcu_is_watching() &&
2051 cpu_online(smp_processor_id()))
2052 invoke_rcu_core();
2053
Pranith Kumarc271d3a2014-07-08 18:26:14 -04002054 return true;
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002055}
2056
2057/*
2058 * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
2059 * not a no-CBs CPU.
2060 */
2061static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07002062 struct rcu_data *rdp,
2063 unsigned long flags)
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002064{
2065 long ql = rsp->qlen;
2066 long qll = rsp->qlen_lazy;
2067
2068 /* If this is not a no-CBs CPU, tell the caller to do it the old way. */
Frederic Weisbeckerd1e43fa2013-03-26 23:47:24 +01002069 if (!rcu_is_nocb_cpu(smp_processor_id()))
Pranith Kumar0a9e1e12014-07-08 18:26:15 -04002070 return false;
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002071 rsp->qlen = 0;
2072 rsp->qlen_lazy = 0;
2073
2074 /* First, enqueue the donelist, if any. This preserves CB ordering. */
2075 if (rsp->orphan_donelist != NULL) {
2076 __call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist,
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07002077 rsp->orphan_donetail, ql, qll, flags);
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002078 ql = qll = 0;
2079 rsp->orphan_donelist = NULL;
2080 rsp->orphan_donetail = &rsp->orphan_donelist;
2081 }
2082 if (rsp->orphan_nxtlist != NULL) {
2083 __call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist,
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07002084 rsp->orphan_nxttail, ql, qll, flags);
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002085 ql = qll = 0;
2086 rsp->orphan_nxtlist = NULL;
2087 rsp->orphan_nxttail = &rsp->orphan_nxtlist;
2088 }
Pranith Kumar0a9e1e12014-07-08 18:26:15 -04002089 return true;
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002090}
2091
2092/*
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002093 * If necessary, kick off a new grace period, and either way wait
2094 * for a subsequent grace period to complete.
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002095 */
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002096static void rcu_nocb_wait_gp(struct rcu_data *rdp)
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002097{
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002098 unsigned long c;
Paul E. McKenneydae6e642013-02-10 20:48:58 -08002099 bool d;
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002100 unsigned long flags;
Paul E. McKenney48a76392014-03-11 13:02:16 -07002101 bool needwake;
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002102 struct rcu_node *rnp = rdp->mynode;
2103
2104 raw_spin_lock_irqsave(&rnp->lock, flags);
Paul E. McKenney6303b9c2013-12-11 13:59:10 -08002105 smp_mb__after_unlock_lock();
Paul E. McKenney48a76392014-03-11 13:02:16 -07002106 needwake = rcu_start_future_gp(rnp, rdp, &c);
Paul E. McKenney0446be42012-12-30 15:21:01 -08002107 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenney48a76392014-03-11 13:02:16 -07002108 if (needwake)
2109 rcu_gp_kthread_wake(rdp->rsp);
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002110
2111 /*
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002112 * Wait for the grace period. Do so interruptibly to avoid messing
2113 * up the load average.
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002114 */
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04002115 trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait"));
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002116 for (;;) {
Paul E. McKenneydae6e642013-02-10 20:48:58 -08002117 wait_event_interruptible(
2118 rnp->nocb_gp_wq[c & 0x1],
2119 (d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c)));
2120 if (likely(d))
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002121 break;
Paul E. McKenney73a860c2014-08-14 10:28:23 -07002122 WARN_ON(signal_pending(current));
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04002123 trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait"));
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002124 }
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04002125 trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait"));
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002126 smp_mb(); /* Ensure that CB invocation happens after GP end. */
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002127}
2128
2129/*
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07002130 * Leaders come here to wait for additional callbacks to show up.
2131 * This function does not return until callbacks appear.
2132 */
2133static void nocb_leader_wait(struct rcu_data *my_rdp)
2134{
2135 bool firsttime = true;
2136 bool gotcbs;
2137 struct rcu_data *rdp;
2138 struct rcu_head **tail;
2139
2140wait_again:
2141
2142 /* Wait for callbacks to appear. */
2143 if (!rcu_nocb_poll) {
2144 trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Sleep");
2145 wait_event_interruptible(my_rdp->nocb_wq,
Pranith Kumar11ed7f92014-08-27 16:43:40 -04002146 !ACCESS_ONCE(my_rdp->nocb_leader_sleep));
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07002147 /* Memory barrier handled by smp_mb() calls below and repoll. */
2148 } else if (firsttime) {
2149 firsttime = false; /* Don't drown trace log with "Poll"! */
2150 trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Poll");
2151 }
2152
2153 /*
2154 * Each pass through the following loop checks a follower for CBs.
2155 * We are our own first follower. Any CBs found are moved to
2156 * nocb_gp_head, where they await a grace period.
2157 */
2158 gotcbs = false;
2159 for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
2160 rdp->nocb_gp_head = ACCESS_ONCE(rdp->nocb_head);
2161 if (!rdp->nocb_gp_head)
2162 continue; /* No CBs here, try next follower. */
2163
2164 /* Move callbacks to wait-for-GP list, which is empty. */
2165 ACCESS_ONCE(rdp->nocb_head) = NULL;
2166 rdp->nocb_gp_tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07002167 gotcbs = true;
2168 }
2169
2170 /*
2171 * If there were no callbacks, sleep a bit, rescan after a
2172 * memory barrier, and go retry.
2173 */
2174 if (unlikely(!gotcbs)) {
2175 if (!rcu_nocb_poll)
2176 trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu,
2177 "WokeEmpty");
Paul E. McKenney73a860c2014-08-14 10:28:23 -07002178 WARN_ON(signal_pending(current));
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07002179 schedule_timeout_interruptible(1);
2180
2181 /* Rescan in case we were a victim of memory ordering. */
Pranith Kumar11ed7f92014-08-27 16:43:40 -04002182 my_rdp->nocb_leader_sleep = true;
2183 smp_mb(); /* Ensure _sleep true before scan. */
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07002184 for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower)
2185 if (ACCESS_ONCE(rdp->nocb_head)) {
2186 /* Found CB, so short-circuit next wait. */
Pranith Kumar11ed7f92014-08-27 16:43:40 -04002187 my_rdp->nocb_leader_sleep = false;
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07002188 break;
2189 }
2190 goto wait_again;
2191 }
2192
2193 /* Wait for one grace period. */
2194 rcu_nocb_wait_gp(my_rdp);
2195
2196 /*
Pranith Kumar11ed7f92014-08-27 16:43:40 -04002197 * We left ->nocb_leader_sleep unset to reduce cache thrashing.
2198 * We set it now, but recheck for new callbacks while
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07002199 * traversing our follower list.
2200 */
Pranith Kumar11ed7f92014-08-27 16:43:40 -04002201 my_rdp->nocb_leader_sleep = true;
2202 smp_mb(); /* Ensure _sleep true before scan of ->nocb_head. */
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07002203
2204 /* Each pass through the following loop wakes a follower, if needed. */
2205 for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
2206 if (ACCESS_ONCE(rdp->nocb_head))
Pranith Kumar11ed7f92014-08-27 16:43:40 -04002207 my_rdp->nocb_leader_sleep = false;/* No need to sleep.*/
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07002208 if (!rdp->nocb_gp_head)
2209 continue; /* No CBs, so no need to wake follower. */
2210
2211 /* Append callbacks to follower's "done" list. */
2212 tail = xchg(&rdp->nocb_follower_tail, rdp->nocb_gp_tail);
2213 *tail = rdp->nocb_gp_head;
Paul E. McKenneyc847f142014-08-12 13:54:21 -07002214 smp_mb__after_atomic(); /* Store *tail before wakeup. */
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07002215 if (rdp != my_rdp && tail == &rdp->nocb_follower_head) {
2216 /*
2217 * List was empty, wake up the follower.
2218 * Memory barriers supplied by atomic_long_add().
2219 */
2220 wake_up(&rdp->nocb_wq);
2221 }
2222 }
2223
2224 /* If we (the leader) don't have CBs, go wait some more. */
2225 if (!my_rdp->nocb_follower_head)
2226 goto wait_again;
2227}
2228
2229/*
2230 * Followers come here to wait for additional callbacks to show up.
2231 * This function does not return until callbacks appear.
2232 */
2233static void nocb_follower_wait(struct rcu_data *rdp)
2234{
2235 bool firsttime = true;
2236
2237 for (;;) {
2238 if (!rcu_nocb_poll) {
2239 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2240 "FollowerSleep");
2241 wait_event_interruptible(rdp->nocb_wq,
2242 ACCESS_ONCE(rdp->nocb_follower_head));
2243 } else if (firsttime) {
2244 /* Don't drown trace log with "Poll"! */
2245 firsttime = false;
2246 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "Poll");
2247 }
2248 if (smp_load_acquire(&rdp->nocb_follower_head)) {
2249 /* ^^^ Ensure CB invocation follows _head test. */
2250 return;
2251 }
2252 if (!rcu_nocb_poll)
2253 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2254 "WokeEmpty");
Paul E. McKenney73a860c2014-08-14 10:28:23 -07002255 WARN_ON(signal_pending(current));
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07002256 schedule_timeout_interruptible(1);
2257 }
2258}
2259
2260/*
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002261 * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07002262 * callbacks queued by the corresponding no-CBs CPU, however, there is
2263 * an optional leader-follower relationship so that the grace-period
2264 * kthreads don't have to do quite so many wakeups.
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002265 */
2266static int rcu_nocb_kthread(void *arg)
2267{
2268 int c, cl;
2269 struct rcu_head *list;
2270 struct rcu_head *next;
2271 struct rcu_head **tail;
2272 struct rcu_data *rdp = arg;
2273
2274 /* Each pass through this loop invokes one batch of callbacks */
2275 for (;;) {
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07002276 /* Wait for callbacks. */
2277 if (rdp->nocb_leader == rdp)
2278 nocb_leader_wait(rdp);
2279 else
2280 nocb_follower_wait(rdp);
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002281
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07002282 /* Pull the ready-to-invoke callbacks onto local list. */
2283 list = ACCESS_ONCE(rdp->nocb_follower_head);
2284 BUG_ON(!list);
2285 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "WokeNonEmpty");
2286 ACCESS_ONCE(rdp->nocb_follower_head) = NULL;
2287 tail = xchg(&rdp->nocb_follower_tail, &rdp->nocb_follower_head);
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002288
2289 /* Each pass through the following loop invokes a callback. */
Paul E. McKenney41050a02014-12-18 12:31:27 -08002290 trace_rcu_batch_start(rdp->rsp->name,
2291 atomic_long_read(&rdp->nocb_q_count_lazy),
2292 atomic_long_read(&rdp->nocb_q_count), -1);
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002293 c = cl = 0;
2294 while (list) {
2295 next = list->next;
2296 /* Wait for enqueuing to complete, if needed. */
2297 while (next == NULL && &list->next != tail) {
Paul E. McKenney69a79bb2013-08-15 13:23:23 -07002298 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2299 TPS("WaitQueue"));
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002300 schedule_timeout_interruptible(1);
Paul E. McKenney69a79bb2013-08-15 13:23:23 -07002301 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2302 TPS("WokeQueue"));
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002303 next = list->next;
2304 }
2305 debug_rcu_head_unqueue(list);
2306 local_bh_disable();
2307 if (__rcu_reclaim(rdp->rsp->name, list))
2308 cl++;
2309 c++;
2310 local_bh_enable();
2311 list = next;
2312 }
2313 trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
Paul E. McKenney41050a02014-12-18 12:31:27 -08002314 smp_mb__before_atomic(); /* _add after CB invocation. */
2315 atomic_long_add(-c, &rdp->nocb_q_count);
2316 atomic_long_add(-cl, &rdp->nocb_q_count_lazy);
Paul E. McKenneyc635a4e12012-10-29 07:29:20 -07002317 rdp->n_nocbs_invoked += c;
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002318 }
2319 return 0;
2320}
2321
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07002322/* Is a deferred wakeup of rcu_nocb_kthread() required? */
Paul E. McKenney9fdd3bc2014-07-29 14:50:47 -07002323static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07002324{
2325 return ACCESS_ONCE(rdp->nocb_defer_wakeup);
2326}
2327
2328/* Do a deferred wakeup of rcu_nocb_kthread(). */
2329static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2330{
Paul E. McKenney9fdd3bc2014-07-29 14:50:47 -07002331 int ndw;
2332
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07002333 if (!rcu_nocb_need_deferred_wakeup(rdp))
2334 return;
Paul E. McKenney9fdd3bc2014-07-29 14:50:47 -07002335 ndw = ACCESS_ONCE(rdp->nocb_defer_wakeup);
2336 ACCESS_ONCE(rdp->nocb_defer_wakeup) = RCU_NOGP_WAKE_NOT;
2337 wake_nocb_leader(rdp, ndw == RCU_NOGP_WAKE_FORCE);
2338 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWake"));
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07002339}
2340
Paul E. McKenneyf4579fc2014-07-25 11:21:47 -07002341void __init rcu_init_nohz(void)
2342{
2343 int cpu;
2344 bool need_rcu_nocb_mask = true;
2345 struct rcu_state *rsp;
2346
2347#ifdef CONFIG_RCU_NOCB_CPU_NONE
2348 need_rcu_nocb_mask = false;
2349#endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
2350
2351#if defined(CONFIG_NO_HZ_FULL)
2352 if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask))
2353 need_rcu_nocb_mask = true;
2354#endif /* #if defined(CONFIG_NO_HZ_FULL) */
2355
2356 if (!have_rcu_nocb_mask && need_rcu_nocb_mask) {
Pranith Kumar949cccd2014-07-25 16:02:07 -07002357 if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
2358 pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
2359 return;
2360 }
Paul E. McKenneyf4579fc2014-07-25 11:21:47 -07002361 have_rcu_nocb_mask = true;
2362 }
2363 if (!have_rcu_nocb_mask)
2364 return;
2365
2366#ifdef CONFIG_RCU_NOCB_CPU_ZERO
2367 pr_info("\tOffload RCU callbacks from CPU 0\n");
2368 cpumask_set_cpu(0, rcu_nocb_mask);
2369#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
2370#ifdef CONFIG_RCU_NOCB_CPU_ALL
2371 pr_info("\tOffload RCU callbacks from all CPUs\n");
2372 cpumask_copy(rcu_nocb_mask, cpu_possible_mask);
2373#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
2374#if defined(CONFIG_NO_HZ_FULL)
2375 if (tick_nohz_full_running)
2376 cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
2377#endif /* #if defined(CONFIG_NO_HZ_FULL) */
2378
2379 if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
2380 pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
2381 cpumask_and(rcu_nocb_mask, cpu_possible_mask,
2382 rcu_nocb_mask);
2383 }
Tejun Heoad853b42015-02-13 14:37:25 -08002384 pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
2385 cpumask_pr_args(rcu_nocb_mask));
Paul E. McKenneyf4579fc2014-07-25 11:21:47 -07002386 if (rcu_nocb_poll)
2387 pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
2388
2389 for_each_rcu_flavor(rsp) {
2390 for_each_cpu(cpu, rcu_nocb_mask) {
2391 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
2392
2393 /*
2394 * If there are early callbacks, they will need
2395 * to be moved to the nocb lists.
2396 */
2397 WARN_ON_ONCE(rdp->nxttail[RCU_NEXT_TAIL] !=
2398 &rdp->nxtlist &&
2399 rdp->nxttail[RCU_NEXT_TAIL] != NULL);
2400 init_nocb_callback_list(rdp);
2401 }
Paul E. McKenney35ce7f22014-07-11 11:30:24 -07002402 rcu_organize_nocb_kthreads(rsp);
Paul E. McKenneyf4579fc2014-07-25 11:21:47 -07002403 }
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002404}
2405
2406/* Initialize per-rcu_data variables for no-CBs CPUs. */
2407static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2408{
2409 rdp->nocb_tail = &rdp->nocb_head;
2410 init_waitqueue_head(&rdp->nocb_wq);
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07002411 rdp->nocb_follower_tail = &rdp->nocb_follower_head;
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002412}
2413
Paul E. McKenney35ce7f22014-07-11 11:30:24 -07002414/*
2415 * If the specified CPU is a no-CBs CPU that does not already have its
2416 * rcuo kthread for the specified RCU flavor, spawn it. If the CPUs are
2417 * brought online out of order, this can require re-organizing the
2418 * leader-follower relationships.
2419 */
2420static void rcu_spawn_one_nocb_kthread(struct rcu_state *rsp, int cpu)
2421{
2422 struct rcu_data *rdp;
2423 struct rcu_data *rdp_last;
2424 struct rcu_data *rdp_old_leader;
2425 struct rcu_data *rdp_spawn = per_cpu_ptr(rsp->rda, cpu);
2426 struct task_struct *t;
2427
2428 /*
2429 * If this isn't a no-CBs CPU or if it already has an rcuo kthread,
2430 * then nothing to do.
2431 */
2432 if (!rcu_is_nocb_cpu(cpu) || rdp_spawn->nocb_kthread)
2433 return;
2434
2435 /* If we didn't spawn the leader first, reorganize! */
2436 rdp_old_leader = rdp_spawn->nocb_leader;
2437 if (rdp_old_leader != rdp_spawn && !rdp_old_leader->nocb_kthread) {
2438 rdp_last = NULL;
2439 rdp = rdp_old_leader;
2440 do {
2441 rdp->nocb_leader = rdp_spawn;
2442 if (rdp_last && rdp != rdp_spawn)
2443 rdp_last->nocb_next_follower = rdp;
Paul E. McKenneybbe5d7a2014-10-24 11:11:08 -07002444 if (rdp == rdp_spawn) {
2445 rdp = rdp->nocb_next_follower;
2446 } else {
2447 rdp_last = rdp;
2448 rdp = rdp->nocb_next_follower;
2449 rdp_last->nocb_next_follower = NULL;
2450 }
Paul E. McKenney35ce7f22014-07-11 11:30:24 -07002451 } while (rdp);
2452 rdp_spawn->nocb_next_follower = rdp_old_leader;
2453 }
2454
2455 /* Spawn the kthread for this CPU and RCU flavor. */
2456 t = kthread_run(rcu_nocb_kthread, rdp_spawn,
2457 "rcuo%c/%d", rsp->abbr, cpu);
2458 BUG_ON(IS_ERR(t));
2459 ACCESS_ONCE(rdp_spawn->nocb_kthread) = t;
2460}
2461
2462/*
2463 * If the specified CPU is a no-CBs CPU that does not already have its
2464 * rcuo kthreads, spawn them.
2465 */
2466static void rcu_spawn_all_nocb_kthreads(int cpu)
2467{
2468 struct rcu_state *rsp;
2469
2470 if (rcu_scheduler_fully_active)
2471 for_each_rcu_flavor(rsp)
2472 rcu_spawn_one_nocb_kthread(rsp, cpu);
2473}
2474
2475/*
2476 * Once the scheduler is running, spawn rcuo kthreads for all online
2477 * no-CBs CPUs. This assumes that the early_initcall()s happen before
2478 * non-boot CPUs come online -- if this changes, we will need to add
2479 * some mutual exclusion.
2480 */
2481static void __init rcu_spawn_nocb_kthreads(void)
2482{
2483 int cpu;
2484
2485 for_each_online_cpu(cpu)
2486 rcu_spawn_all_nocb_kthreads(cpu);
2487}
2488
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07002489/* How many follower CPU IDs per leader? Default of -1 for sqrt(nr_cpu_ids). */
2490static int rcu_nocb_leader_stride = -1;
2491module_param(rcu_nocb_leader_stride, int, 0444);
2492
2493/*
Paul E. McKenney35ce7f22014-07-11 11:30:24 -07002494 * Initialize leader-follower relationships for all no-CBs CPU.
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07002495 */
Paul E. McKenney35ce7f22014-07-11 11:30:24 -07002496static void __init rcu_organize_nocb_kthreads(struct rcu_state *rsp)
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002497{
2498 int cpu;
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07002499 int ls = rcu_nocb_leader_stride;
2500 int nl = 0; /* Next leader. */
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002501 struct rcu_data *rdp;
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07002502 struct rcu_data *rdp_leader = NULL; /* Suppress misguided gcc warn. */
2503 struct rcu_data *rdp_prev = NULL;
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002504
Pranith Kumar22c2f662014-07-17 20:11:01 -04002505 if (!have_rcu_nocb_mask)
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002506 return;
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07002507 if (ls == -1) {
2508 ls = int_sqrt(nr_cpu_ids);
2509 rcu_nocb_leader_stride = ls;
2510 }
2511
2512 /*
2513 * Each pass through this loop sets up one rcu_data structure and
2514 * spawns one rcu_nocb_kthread().
2515 */
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002516 for_each_cpu(cpu, rcu_nocb_mask) {
2517 rdp = per_cpu_ptr(rsp->rda, cpu);
Paul E. McKenneyfbce7492014-06-24 09:26:11 -07002518 if (rdp->cpu >= nl) {
2519 /* New leader, set up for followers & next leader. */
2520 nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
2521 rdp->nocb_leader = rdp;
2522 rdp_leader = rdp;
2523 } else {
2524 /* Another follower, link to previous leader. */
2525 rdp->nocb_leader = rdp_leader;
2526 rdp_prev->nocb_next_follower = rdp;
2527 }
2528 rdp_prev = rdp;
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002529 }
2530}
2531
2532/* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002533static bool init_nocb_callback_list(struct rcu_data *rdp)
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002534{
Pranith Kumar22c2f662014-07-17 20:11:01 -04002535 if (!rcu_is_nocb_cpu(rdp->cpu))
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002536 return false;
Pranith Kumar22c2f662014-07-17 20:11:01 -04002537
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002538 rdp->nxttail[RCU_NEXT_TAIL] = NULL;
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002539 return true;
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002540}
2541
2542#else /* #ifdef CONFIG_RCU_NOCB_CPU */
2543
Paul E. McKenneyd7e29932014-10-27 09:15:54 -07002544static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
2545{
2546 WARN_ON_ONCE(1); /* Should be dead code. */
2547 return false;
2548}
2549
Paul E. McKenney0446be42012-12-30 15:21:01 -08002550static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
Paul E. McKenneydae6e642013-02-10 20:48:58 -08002551{
Paul E. McKenneydae6e642013-02-10 20:48:58 -08002552}
2553
2554static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
2555{
2556}
2557
2558static void rcu_init_one_nocb(struct rcu_node *rnp)
2559{
2560}
2561
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002562static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07002563 bool lazy, unsigned long flags)
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002564{
Pranith Kumar4afc7e22014-07-08 18:26:16 -04002565 return false;
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002566}
2567
2568static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07002569 struct rcu_data *rdp,
2570 unsigned long flags)
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002571{
Pranith Kumarf4aa84b2014-07-08 18:26:17 -04002572 return false;
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002573}
2574
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002575static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2576{
2577}
2578
Paul E. McKenney9fdd3bc2014-07-29 14:50:47 -07002579static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07002580{
2581 return false;
2582}
2583
2584static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2585{
2586}
2587
Paul E. McKenney35ce7f22014-07-11 11:30:24 -07002588static void rcu_spawn_all_nocb_kthreads(int cpu)
2589{
2590}
2591
2592static void __init rcu_spawn_nocb_kthreads(void)
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002593{
2594}
2595
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002596static bool init_nocb_callback_list(struct rcu_data *rdp)
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002597{
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002598 return false;
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002599}
2600
2601#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
Paul E. McKenney65d798f2013-04-12 16:19:10 -07002602
2603/*
2604 * An adaptive-ticks CPU can potentially execute in kernel mode for an
2605 * arbitrarily long period of time with the scheduling-clock tick turned
2606 * off. RCU will be paying attention to this CPU because it is in the
2607 * kernel, but the CPU cannot be guaranteed to be executing the RCU state
2608 * machine because the scheduling-clock tick has been disabled. Therefore,
2609 * if an adaptive-ticks CPU is failing to respond to the current grace
2610 * period and has not be idle from an RCU perspective, kick it.
2611 */
Paul E. McKenney4a81e832014-06-20 16:49:01 -07002612static void __maybe_unused rcu_kick_nohz_cpu(int cpu)
Paul E. McKenney65d798f2013-04-12 16:19:10 -07002613{
2614#ifdef CONFIG_NO_HZ_FULL
2615 if (tick_nohz_full_cpu(cpu))
2616 smp_send_reschedule(cpu);
2617#endif /* #ifdef CONFIG_NO_HZ_FULL */
2618}
Paul E. McKenney23332102013-06-21 12:34:33 -07002619
2620
2621#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
2622
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07002623static int full_sysidle_state; /* Current system-idle state. */
Paul E. McKenneyd4bd54f2013-06-21 14:51:40 -07002624#define RCU_SYSIDLE_NOT 0 /* Some CPU is not idle. */
2625#define RCU_SYSIDLE_SHORT 1 /* All CPUs idle for brief period. */
2626#define RCU_SYSIDLE_LONG 2 /* All CPUs idle for long enough. */
2627#define RCU_SYSIDLE_FULL 3 /* All CPUs idle, ready for sysidle. */
2628#define RCU_SYSIDLE_FULL_NOTED 4 /* Actually entered sysidle state. */
2629
2630/*
Paul E. McKenneyeb348b82013-06-21 13:00:57 -07002631 * Invoked to note exit from irq or task transition to idle. Note that
2632 * usermode execution does -not- count as idle here! After all, we want
2633 * to detect full-system idle states, not RCU quiescent states and grace
2634 * periods. The caller must have disabled interrupts.
2635 */
Christoph Lameter28ced792014-09-02 14:13:44 -07002636static void rcu_sysidle_enter(int irq)
Paul E. McKenneyeb348b82013-06-21 13:00:57 -07002637{
2638 unsigned long j;
Christoph Lameter28ced792014-09-02 14:13:44 -07002639 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
Paul E. McKenneyeb348b82013-06-21 13:00:57 -07002640
Paul E. McKenney663e1312014-07-21 11:34:33 -07002641 /* If there are no nohz_full= CPUs, no need to track this. */
2642 if (!tick_nohz_full_enabled())
2643 return;
2644
Paul E. McKenneyeb348b82013-06-21 13:00:57 -07002645 /* Adjust nesting, check for fully idle. */
2646 if (irq) {
2647 rdtp->dynticks_idle_nesting--;
2648 WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
2649 if (rdtp->dynticks_idle_nesting != 0)
2650 return; /* Still not fully idle. */
2651 } else {
2652 if ((rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) ==
2653 DYNTICK_TASK_NEST_VALUE) {
2654 rdtp->dynticks_idle_nesting = 0;
2655 } else {
2656 rdtp->dynticks_idle_nesting -= DYNTICK_TASK_NEST_VALUE;
2657 WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
2658 return; /* Still not fully idle. */
2659 }
2660 }
2661
2662 /* Record start of fully idle period. */
2663 j = jiffies;
2664 ACCESS_ONCE(rdtp->dynticks_idle_jiffies) = j;
Peter Zijlstra4e857c52014-03-17 18:06:10 +01002665 smp_mb__before_atomic();
Paul E. McKenneyeb348b82013-06-21 13:00:57 -07002666 atomic_inc(&rdtp->dynticks_idle);
Peter Zijlstra4e857c52014-03-17 18:06:10 +01002667 smp_mb__after_atomic();
Paul E. McKenneyeb348b82013-06-21 13:00:57 -07002668 WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1);
2669}
2670
2671/*
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07002672 * Unconditionally force exit from full system-idle state. This is
2673 * invoked when a normal CPU exits idle, but must be called separately
2674 * for the timekeeping CPU (tick_do_timer_cpu). The reason for this
2675 * is that the timekeeping CPU is permitted to take scheduling-clock
2676 * interrupts while the system is in system-idle state, and of course
2677 * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock
2678 * interrupt from any other type of interrupt.
2679 */
2680void rcu_sysidle_force_exit(void)
2681{
2682 int oldstate = ACCESS_ONCE(full_sysidle_state);
2683 int newoldstate;
2684
2685 /*
2686 * Each pass through the following loop attempts to exit full
2687 * system-idle state. If contention proves to be a problem,
2688 * a trylock-based contention tree could be used here.
2689 */
2690 while (oldstate > RCU_SYSIDLE_SHORT) {
2691 newoldstate = cmpxchg(&full_sysidle_state,
2692 oldstate, RCU_SYSIDLE_NOT);
2693 if (oldstate == newoldstate &&
2694 oldstate == RCU_SYSIDLE_FULL_NOTED) {
2695 rcu_kick_nohz_cpu(tick_do_timer_cpu);
2696 return; /* We cleared it, done! */
2697 }
2698 oldstate = newoldstate;
2699 }
2700 smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */
2701}
2702
2703/*
Paul E. McKenneyeb348b82013-06-21 13:00:57 -07002704 * Invoked to note entry to irq or task transition from idle. Note that
2705 * usermode execution does -not- count as idle here! The caller must
2706 * have disabled interrupts.
2707 */
Christoph Lameter28ced792014-09-02 14:13:44 -07002708static void rcu_sysidle_exit(int irq)
Paul E. McKenneyeb348b82013-06-21 13:00:57 -07002709{
Christoph Lameter28ced792014-09-02 14:13:44 -07002710 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
2711
Paul E. McKenney663e1312014-07-21 11:34:33 -07002712 /* If there are no nohz_full= CPUs, no need to track this. */
2713 if (!tick_nohz_full_enabled())
2714 return;
2715
Paul E. McKenneyeb348b82013-06-21 13:00:57 -07002716 /* Adjust nesting, check for already non-idle. */
2717 if (irq) {
2718 rdtp->dynticks_idle_nesting++;
2719 WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
2720 if (rdtp->dynticks_idle_nesting != 1)
2721 return; /* Already non-idle. */
2722 } else {
2723 /*
2724 * Allow for irq misnesting. Yes, it really is possible
2725 * to enter an irq handler then never leave it, and maybe
2726 * also vice versa. Handle both possibilities.
2727 */
2728 if (rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) {
2729 rdtp->dynticks_idle_nesting += DYNTICK_TASK_NEST_VALUE;
2730 WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
2731 return; /* Already non-idle. */
2732 } else {
2733 rdtp->dynticks_idle_nesting = DYNTICK_TASK_EXIT_IDLE;
2734 }
2735 }
2736
2737 /* Record end of idle period. */
Peter Zijlstra4e857c52014-03-17 18:06:10 +01002738 smp_mb__before_atomic();
Paul E. McKenneyeb348b82013-06-21 13:00:57 -07002739 atomic_inc(&rdtp->dynticks_idle);
Peter Zijlstra4e857c52014-03-17 18:06:10 +01002740 smp_mb__after_atomic();
Paul E. McKenneyeb348b82013-06-21 13:00:57 -07002741 WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1));
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07002742
2743 /*
2744 * If we are the timekeeping CPU, we are permitted to be non-idle
2745 * during a system-idle state. This must be the case, because
2746 * the timekeeping CPU has to take scheduling-clock interrupts
2747 * during the time that the system is transitioning to full
2748 * system-idle state. This means that the timekeeping CPU must
2749 * invoke rcu_sysidle_force_exit() directly if it does anything
2750 * more than take a scheduling-clock interrupt.
2751 */
2752 if (smp_processor_id() == tick_do_timer_cpu)
2753 return;
2754
2755 /* Update system-idle state: We are clearly no longer fully idle! */
2756 rcu_sysidle_force_exit();
2757}
2758
2759/*
2760 * Check to see if the current CPU is idle. Note that usermode execution
2761 * does not count as idle. The caller must have disabled interrupts.
2762 */
2763static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
2764 unsigned long *maxj)
2765{
2766 int cur;
2767 unsigned long j;
2768 struct rcu_dynticks *rdtp = rdp->dynticks;
2769
Paul E. McKenney663e1312014-07-21 11:34:33 -07002770 /* If there are no nohz_full= CPUs, don't check system-wide idleness. */
2771 if (!tick_nohz_full_enabled())
2772 return;
2773
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07002774 /*
2775 * If some other CPU has already reported non-idle, if this is
2776 * not the flavor of RCU that tracks sysidle state, or if this
2777 * is an offline or the timekeeping CPU, nothing to do.
2778 */
Paul E. McKenney417e8d22014-07-21 11:26:54 -07002779 if (!*isidle || rdp->rsp != rcu_state_p ||
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07002780 cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
2781 return;
Paul E. McKenneyeb757672013-06-21 17:10:40 -07002782 if (rcu_gp_in_progress(rdp->rsp))
2783 WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu);
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07002784
2785 /* Pick up current idle and NMI-nesting counter and check. */
2786 cur = atomic_read(&rdtp->dynticks_idle);
2787 if (cur & 0x1) {
2788 *isidle = false; /* We are not idle! */
2789 return;
2790 }
2791 smp_mb(); /* Read counters before timestamps. */
2792
2793 /* Pick up timestamps. */
2794 j = ACCESS_ONCE(rdtp->dynticks_idle_jiffies);
2795 /* If this CPU entered idle more recently, update maxj timestamp. */
2796 if (ULONG_CMP_LT(*maxj, j))
2797 *maxj = j;
2798}
2799
2800/*
2801 * Is this the flavor of RCU that is handling full-system idle?
2802 */
2803static bool is_sysidle_rcu_state(struct rcu_state *rsp)
2804{
Paul E. McKenney417e8d22014-07-21 11:26:54 -07002805 return rsp == rcu_state_p;
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07002806}
2807
2808/*
2809 * Return a delay in jiffies based on the number of CPUs, rcu_node
2810 * leaf fanout, and jiffies tick rate. The idea is to allow larger
2811 * systems more time to transition to full-idle state in order to
2812 * avoid the cache thrashing that otherwise occur on the state variable.
2813 * Really small systems (less than a couple of tens of CPUs) should
2814 * instead use a single global atomically incremented counter, and later
2815 * versions of this will automatically reconfigure themselves accordingly.
2816 */
2817static unsigned long rcu_sysidle_delay(void)
2818{
2819 if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
2820 return 0;
2821 return DIV_ROUND_UP(nr_cpu_ids * HZ, rcu_fanout_leaf * 1000);
2822}
2823
2824/*
2825 * Advance the full-system-idle state. This is invoked when all of
2826 * the non-timekeeping CPUs are idle.
2827 */
2828static void rcu_sysidle(unsigned long j)
2829{
2830 /* Check the current state. */
2831 switch (ACCESS_ONCE(full_sysidle_state)) {
2832 case RCU_SYSIDLE_NOT:
2833
2834 /* First time all are idle, so note a short idle period. */
2835 ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_SHORT;
2836 break;
2837
2838 case RCU_SYSIDLE_SHORT:
2839
2840 /*
2841 * Idle for a bit, time to advance to next state?
2842 * cmpxchg failure means race with non-idle, let them win.
2843 */
2844 if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
2845 (void)cmpxchg(&full_sysidle_state,
2846 RCU_SYSIDLE_SHORT, RCU_SYSIDLE_LONG);
2847 break;
2848
2849 case RCU_SYSIDLE_LONG:
2850
2851 /*
2852 * Do an additional check pass before advancing to full.
2853 * cmpxchg failure means race with non-idle, let them win.
2854 */
2855 if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
2856 (void)cmpxchg(&full_sysidle_state,
2857 RCU_SYSIDLE_LONG, RCU_SYSIDLE_FULL);
2858 break;
2859
2860 default:
2861 break;
2862 }
2863}
2864
2865/*
2866 * Found a non-idle non-timekeeping CPU, so kick the system-idle state
2867 * back to the beginning.
2868 */
2869static void rcu_sysidle_cancel(void)
2870{
2871 smp_mb();
Paul E. McKenneybecb41b2014-04-07 13:34:07 -07002872 if (full_sysidle_state > RCU_SYSIDLE_SHORT)
2873 ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_NOT;
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07002874}
2875
2876/*
2877 * Update the sysidle state based on the results of a force-quiescent-state
2878 * scan of the CPUs' dyntick-idle state.
2879 */
2880static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
2881 unsigned long maxj, bool gpkt)
2882{
Paul E. McKenney417e8d22014-07-21 11:26:54 -07002883 if (rsp != rcu_state_p)
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07002884 return; /* Wrong flavor, ignore. */
2885 if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
2886 return; /* Running state machine from timekeeping CPU. */
2887 if (isidle)
2888 rcu_sysidle(maxj); /* More idle! */
2889 else
2890 rcu_sysidle_cancel(); /* Idle is over. */
2891}
2892
2893/*
2894 * Wrapper for rcu_sysidle_report() when called from the grace-period
2895 * kthread's context.
2896 */
2897static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
2898 unsigned long maxj)
2899{
Paul E. McKenney663e1312014-07-21 11:34:33 -07002900 /* If there are no nohz_full= CPUs, no need to track this. */
2901 if (!tick_nohz_full_enabled())
2902 return;
2903
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07002904 rcu_sysidle_report(rsp, isidle, maxj, true);
2905}
2906
2907/* Callback and function for forcing an RCU grace period. */
2908struct rcu_sysidle_head {
2909 struct rcu_head rh;
2910 int inuse;
2911};
2912
2913static void rcu_sysidle_cb(struct rcu_head *rhp)
2914{
2915 struct rcu_sysidle_head *rshp;
2916
2917 /*
2918 * The following memory barrier is needed to replace the
2919 * memory barriers that would normally be in the memory
2920 * allocator.
2921 */
2922 smp_mb(); /* grace period precedes setting inuse. */
2923
2924 rshp = container_of(rhp, struct rcu_sysidle_head, rh);
2925 ACCESS_ONCE(rshp->inuse) = 0;
2926}
2927
2928/*
2929 * Check to see if the system is fully idle, other than the timekeeping CPU.
Paul E. McKenney663e1312014-07-21 11:34:33 -07002930 * The caller must have disabled interrupts. This is not intended to be
2931 * called unless tick_nohz_full_enabled().
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07002932 */
2933bool rcu_sys_is_idle(void)
2934{
2935 static struct rcu_sysidle_head rsh;
2936 int rss = ACCESS_ONCE(full_sysidle_state);
2937
2938 if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu))
2939 return false;
2940
2941 /* Handle small-system case by doing a full scan of CPUs. */
2942 if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) {
2943 int oldrss = rss - 1;
2944
2945 /*
2946 * One pass to advance to each state up to _FULL.
2947 * Give up if any pass fails to advance the state.
2948 */
2949 while (rss < RCU_SYSIDLE_FULL && oldrss < rss) {
2950 int cpu;
2951 bool isidle = true;
2952 unsigned long maxj = jiffies - ULONG_MAX / 4;
2953 struct rcu_data *rdp;
2954
2955 /* Scan all the CPUs looking for nonidle CPUs. */
2956 for_each_possible_cpu(cpu) {
Paul E. McKenney417e8d22014-07-21 11:26:54 -07002957 rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07002958 rcu_sysidle_check_cpu(rdp, &isidle, &maxj);
2959 if (!isidle)
2960 break;
2961 }
Paul E. McKenney417e8d22014-07-21 11:26:54 -07002962 rcu_sysidle_report(rcu_state_p, isidle, maxj, false);
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07002963 oldrss = rss;
2964 rss = ACCESS_ONCE(full_sysidle_state);
2965 }
2966 }
2967
2968 /* If this is the first observation of an idle period, record it. */
2969 if (rss == RCU_SYSIDLE_FULL) {
2970 rss = cmpxchg(&full_sysidle_state,
2971 RCU_SYSIDLE_FULL, RCU_SYSIDLE_FULL_NOTED);
2972 return rss == RCU_SYSIDLE_FULL;
2973 }
2974
2975 smp_mb(); /* ensure rss load happens before later caller actions. */
2976
2977 /* If already fully idle, tell the caller (in case of races). */
2978 if (rss == RCU_SYSIDLE_FULL_NOTED)
2979 return true;
2980
2981 /*
2982 * If we aren't there yet, and a grace period is not in flight,
2983 * initiate a grace period. Either way, tell the caller that
2984 * we are not there yet. We use an xchg() rather than an assignment
2985 * to make up for the memory barriers that would otherwise be
2986 * provided by the memory allocator.
2987 */
2988 if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL &&
Paul E. McKenney417e8d22014-07-21 11:26:54 -07002989 !rcu_gp_in_progress(rcu_state_p) &&
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07002990 !rsh.inuse && xchg(&rsh.inuse, 1) == 0)
2991 call_rcu(&rsh.rh, rcu_sysidle_cb);
2992 return false;
Paul E. McKenneyeb348b82013-06-21 13:00:57 -07002993}
2994
2995/*
Paul E. McKenney23332102013-06-21 12:34:33 -07002996 * Initialize dynticks sysidle state for CPUs coming online.
2997 */
2998static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
2999{
3000 rdtp->dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE;
3001}
3002
3003#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
3004
Christoph Lameter28ced792014-09-02 14:13:44 -07003005static void rcu_sysidle_enter(int irq)
Paul E. McKenneyeb348b82013-06-21 13:00:57 -07003006{
3007}
3008
Christoph Lameter28ced792014-09-02 14:13:44 -07003009static void rcu_sysidle_exit(int irq)
Paul E. McKenneyeb348b82013-06-21 13:00:57 -07003010{
3011}
3012
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07003013static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
3014 unsigned long *maxj)
3015{
3016}
3017
3018static bool is_sysidle_rcu_state(struct rcu_state *rsp)
3019{
3020 return false;
3021}
3022
3023static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
3024 unsigned long maxj)
3025{
3026}
3027
Paul E. McKenney23332102013-06-21 12:34:33 -07003028static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
3029{
3030}
3031
3032#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
Paul E. McKenneya0969322013-11-08 09:03:10 -08003033
3034/*
3035 * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
3036 * grace-period kthread will do force_quiescent_state() processing?
3037 * The idea is to avoid waking up RCU core processing on such a
3038 * CPU unless the grace period has extended for too long.
3039 *
3040 * This code relies on the fact that all NO_HZ_FULL CPUs are also
Paul Bolle52e2bb92014-02-09 14:35:11 +01003041 * CONFIG_RCU_NOCB_CPU CPUs.
Paul E. McKenneya0969322013-11-08 09:03:10 -08003042 */
3043static bool rcu_nohz_full_cpu(struct rcu_state *rsp)
3044{
3045#ifdef CONFIG_NO_HZ_FULL
3046 if (tick_nohz_full_cpu(smp_processor_id()) &&
3047 (!rcu_gp_in_progress(rsp) ||
3048 ULONG_CMP_LT(jiffies, ACCESS_ONCE(rsp->gp_start) + HZ)))
3049 return 1;
3050#endif /* #ifdef CONFIG_NO_HZ_FULL */
3051 return 0;
3052}
Paul E. McKenney5057f55e52014-04-01 11:20:36 -07003053
3054/*
3055 * Bind the grace-period kthread for the sysidle flavor of RCU to the
3056 * timekeeping CPU.
3057 */
3058static void rcu_bind_gp_kthread(void)
3059{
Paul E. McKenneyc0f489d2014-06-04 13:46:03 -07003060 int __maybe_unused cpu;
Paul E. McKenney5057f55e52014-04-01 11:20:36 -07003061
Paul E. McKenneyc0f489d2014-06-04 13:46:03 -07003062 if (!tick_nohz_full_enabled())
Paul E. McKenney5057f55e52014-04-01 11:20:36 -07003063 return;
Paul E. McKenneyc0f489d2014-06-04 13:46:03 -07003064#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
3065 cpu = tick_do_timer_cpu;
3066 if (cpu >= 0 && cpu < nr_cpu_ids && raw_smp_processor_id() != cpu)
Paul E. McKenney5057f55e52014-04-01 11:20:36 -07003067 set_cpus_allowed_ptr(current, cpumask_of(cpu));
Paul E. McKenneyc0f489d2014-06-04 13:46:03 -07003068#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
3069 if (!is_housekeeping_cpu(raw_smp_processor_id()))
3070 housekeeping_affine(current);
3071#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
Paul E. McKenney5057f55e52014-04-01 11:20:36 -07003072}
Paul E. McKenney176f8f72014-08-04 17:43:50 -07003073
3074/* Record the current task on dyntick-idle entry. */
3075static void rcu_dynticks_task_enter(void)
3076{
3077#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
3078 ACCESS_ONCE(current->rcu_tasks_idle_cpu) = smp_processor_id();
3079#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
3080}
3081
3082/* Record no current task on dyntick-idle exit. */
3083static void rcu_dynticks_task_exit(void)
3084{
3085#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
3086 ACCESS_ONCE(current->rcu_tasks_idle_cpu) = -1;
3087#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
3088}