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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#define RCU_KTHREAD_PRIO 1
34
35#ifdef CONFIG_RCU_BOOST
Paul E. McKenneyabaa93d2014-06-12 13:30:25 -070036#include "../locking/rtmutex_common.h"
Mike Galbraith5b61b0b2011-08-19 11:39:11 -070037#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
38#else
39#define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
40#endif
41
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -070042#ifdef CONFIG_RCU_NOCB_CPU
43static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
44static bool have_rcu_nocb_mask; /* Was rcu_nocb_mask allocated? */
Paul Gortmaker1b0048a2012-12-20 13:19:22 -080045static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -070046static char __initdata nocb_buf[NR_CPUS * 5];
47#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
48
Paul E. McKenney26845c22010-04-13 14:19:23 -070049/*
50 * Check the RCU kernel configuration parameters and print informative
51 * messages about anything out of the ordinary. If you like #ifdef, you
52 * will love this function.
53 */
54static void __init rcu_bootup_announce_oddness(void)
55{
56#ifdef CONFIG_RCU_TRACE
Paul E. McKenneyefc151c2013-03-18 16:24:11 -070057 pr_info("\tRCU debugfs-based tracing is enabled.\n");
Paul E. McKenney26845c22010-04-13 14:19:23 -070058#endif
59#if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
Paul E. McKenneyefc151c2013-03-18 16:24:11 -070060 pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
Paul E. McKenney26845c22010-04-13 14:19:23 -070061 CONFIG_RCU_FANOUT);
62#endif
63#ifdef CONFIG_RCU_FANOUT_EXACT
Paul E. McKenneyefc151c2013-03-18 16:24:11 -070064 pr_info("\tHierarchical RCU autobalancing is disabled.\n");
Paul E. McKenney26845c22010-04-13 14:19:23 -070065#endif
66#ifdef CONFIG_RCU_FAST_NO_HZ
Paul E. McKenneyefc151c2013-03-18 16:24:11 -070067 pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
Paul E. McKenney26845c22010-04-13 14:19:23 -070068#endif
69#ifdef CONFIG_PROVE_RCU
Paul E. McKenneyefc151c2013-03-18 16:24:11 -070070 pr_info("\tRCU lockdep checking is enabled.\n");
Paul E. McKenney26845c22010-04-13 14:19:23 -070071#endif
72#ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
Paul E. McKenneyefc151c2013-03-18 16:24:11 -070073 pr_info("\tRCU torture testing starts during boot.\n");
Paul E. McKenney26845c22010-04-13 14:19:23 -070074#endif
Paul E. McKenney81a294c2010-08-30 09:52:50 -070075#if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
Paul E. McKenneyefc151c2013-03-18 16:24:11 -070076 pr_info("\tDump stacks of tasks blocking RCU-preempt GP.\n");
Paul E. McKenneya858af22012-01-16 13:29:10 -080077#endif
78#if defined(CONFIG_RCU_CPU_STALL_INFO)
Paul E. McKenneyefc151c2013-03-18 16:24:11 -070079 pr_info("\tAdditional per-CPU info printed with stalls.\n");
Paul E. McKenney26845c22010-04-13 14:19:23 -070080#endif
81#if NUM_RCU_LVL_4 != 0
Paul E. McKenneyefc151c2013-03-18 16:24:11 -070082 pr_info("\tFour-level hierarchy is enabled.\n");
Paul E. McKenney26845c22010-04-13 14:19:23 -070083#endif
Paul E. McKenneyf885b7f2012-04-23 15:52:53 -070084 if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF)
Paul E. McKenney9a5739d2013-03-28 20:48:36 -070085 pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
Paul E. McKenneycca6f392012-05-08 21:00:28 -070086 if (nr_cpu_ids != NR_CPUS)
Paul E. McKenneyefc151c2013-03-18 16:24:11 -070087 pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -070088#ifdef CONFIG_RCU_NOCB_CPU
Paul E. McKenney911af502013-02-11 10:23:27 -080089#ifndef CONFIG_RCU_NOCB_CPU_NONE
90 if (!have_rcu_nocb_mask) {
Sasha Levin615ee542013-03-26 11:35:16 -040091 zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL);
Paul E. McKenney911af502013-02-11 10:23:27 -080092 have_rcu_nocb_mask = true;
93 }
94#ifdef CONFIG_RCU_NOCB_CPU_ZERO
Paul E. McKenney9a5739d2013-03-28 20:48:36 -070095 pr_info("\tOffload RCU callbacks from CPU 0\n");
Paul E. McKenney911af502013-02-11 10:23:27 -080096 cpumask_set_cpu(0, rcu_nocb_mask);
97#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
98#ifdef CONFIG_RCU_NOCB_CPU_ALL
Paul E. McKenney9a5739d2013-03-28 20:48:36 -070099 pr_info("\tOffload RCU callbacks from all CPUs\n");
Kirill Tkhai5d5a0802013-09-15 17:29:17 +0400100 cpumask_copy(rcu_nocb_mask, cpu_possible_mask);
Paul E. McKenney911af502013-02-11 10:23:27 -0800101#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
102#endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -0700103 if (have_rcu_nocb_mask) {
Kirill Tkhai5d5a0802013-09-15 17:29:17 +0400104 if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
105 pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
106 cpumask_and(rcu_nocb_mask, cpu_possible_mask,
107 rcu_nocb_mask);
108 }
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -0700109 cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask);
Paul E. McKenney9a5739d2013-03-28 20:48:36 -0700110 pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf);
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -0700111 if (rcu_nocb_poll)
Paul E. McKenney9a5739d2013-03-28 20:48:36 -0700112 pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -0700113 }
114#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
Paul E. McKenney26845c22010-04-13 14:19:23 -0700115}
116
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700117#ifdef CONFIG_TREE_PREEMPT_RCU
118
Steven Rostedt (Red Hat)a41bfeb2013-07-12 17:00:28 -0400119RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu);
Uma Sharmae5341652014-03-23 22:32:09 -0700120static struct rcu_state *rcu_state_p = &rcu_preempt_state;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700121
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800122static int rcu_preempted_readers_exp(struct rcu_node *rnp);
123
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700124/*
125 * Tell them what RCU they are running.
126 */
Paul E. McKenney0e0fc1c2009-11-11 11:28:06 -0800127static void __init rcu_bootup_announce(void)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700128{
Paul E. McKenneyefc151c2013-03-18 16:24:11 -0700129 pr_info("Preemptible hierarchical RCU implementation.\n");
Paul E. McKenney26845c22010-04-13 14:19:23 -0700130 rcu_bootup_announce_oddness();
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700131}
132
133/*
134 * Return the number of RCU-preempt batches processed thus far
135 * for debug and statistics.
136 */
137long rcu_batches_completed_preempt(void)
138{
139 return rcu_preempt_state.completed;
140}
141EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt);
142
143/*
144 * Return the number of RCU batches processed thus far for debug & stats.
145 */
146long rcu_batches_completed(void)
147{
148 return rcu_batches_completed_preempt();
149}
150EXPORT_SYMBOL_GPL(rcu_batches_completed);
151
152/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800153 * Record a preemptible-RCU quiescent state for the specified CPU. Note
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700154 * that this just means that the task currently running on the CPU is
155 * not in a quiescent state. There might be any number of tasks blocked
156 * while in an RCU read-side critical section.
Paul E. McKenney25502a62010-04-01 17:37:01 -0700157 *
158 * Unlike the other rcu_*_qs() functions, callers to this function
159 * must disable irqs in order to protect the assignment to
160 * ->rcu_read_unlock_special.
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700161 */
Paul E. McKenneyc3422be2009-09-13 09:15:10 -0700162static void rcu_preempt_qs(int cpu)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700163{
164 struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
Paul E. McKenney25502a62010-04-01 17:37:01 -0700165
Paul E. McKenneye4cc1f22011-06-27 00:17:43 -0700166 if (rdp->passed_quiesce == 0)
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -0400167 trace_rcu_grace_period(TPS("rcu_preempt"), rdp->gpnum, TPS("cpuqs"));
Paul E. McKenneye4cc1f22011-06-27 00:17:43 -0700168 rdp->passed_quiesce = 1;
Paul E. McKenney25502a62010-04-01 17:37:01 -0700169 current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700170}
171
172/*
Paul E. McKenneyc3422be2009-09-13 09:15:10 -0700173 * We have entered the scheduler, and the current task might soon be
174 * context-switched away from. If this task is in an RCU read-side
175 * critical section, we will no longer be able to rely on the CPU to
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800176 * record that fact, so we enqueue the task on the blkd_tasks list.
177 * The task will dequeue itself when it exits the outermost enclosing
178 * RCU read-side critical section. Therefore, the current grace period
179 * cannot be permitted to complete until the blkd_tasks list entries
180 * predating the current grace period drain, in other words, until
181 * rnp->gp_tasks becomes NULL.
Paul E. McKenneyc3422be2009-09-13 09:15:10 -0700182 *
183 * Caller must disable preemption.
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700184 */
Paul E. McKenneycba6d0d2012-07-02 07:08:42 -0700185static void rcu_preempt_note_context_switch(int cpu)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700186{
187 struct task_struct *t = current;
Paul E. McKenneyc3422be2009-09-13 09:15:10 -0700188 unsigned long flags;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700189 struct rcu_data *rdp;
190 struct rcu_node *rnp;
191
Paul E. McKenney10f39bb2011-07-17 21:14:35 -0700192 if (t->rcu_read_lock_nesting > 0 &&
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700193 (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
194
195 /* Possibly blocking in an RCU read-side critical section. */
Paul E. McKenneycba6d0d2012-07-02 07:08:42 -0700196 rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700197 rnp = rdp->mynode;
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800198 raw_spin_lock_irqsave(&rnp->lock, flags);
Paul E. McKenney6303b9c2013-12-11 13:59:10 -0800199 smp_mb__after_unlock_lock();
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700200 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
Paul E. McKenney86848962009-08-27 15:00:12 -0700201 t->rcu_blocked_node = rnp;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700202
203 /*
204 * If this CPU has already checked in, then this task
205 * will hold up the next grace period rather than the
206 * current grace period. Queue the task accordingly.
207 * If the task is queued for the current grace period
208 * (i.e., this CPU has not yet passed through a quiescent
209 * state for the current grace period), then as long
210 * as that task remains queued, the current grace period
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800211 * cannot end. Note that there is some uncertainty as
212 * to exactly when the current grace period started.
213 * We take a conservative approach, which can result
214 * in unnecessarily waiting on tasks that started very
215 * slightly after the current grace period began. C'est
216 * la vie!!!
Paul E. McKenneyb0e165c2009-09-13 09:15:09 -0700217 *
218 * But first, note that the current CPU must still be
219 * on line!
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700220 */
Paul E. McKenneyb0e165c2009-09-13 09:15:09 -0700221 WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);
Paul E. McKenneye7d88422009-09-18 09:50:18 -0700222 WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800223 if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) {
224 list_add(&t->rcu_node_entry, rnp->gp_tasks->prev);
225 rnp->gp_tasks = &t->rcu_node_entry;
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800226#ifdef CONFIG_RCU_BOOST
227 if (rnp->boost_tasks != NULL)
228 rnp->boost_tasks = rnp->gp_tasks;
229#endif /* #ifdef CONFIG_RCU_BOOST */
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800230 } else {
231 list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
232 if (rnp->qsmask & rdp->grpmask)
233 rnp->gp_tasks = &t->rcu_node_entry;
234 }
Paul E. McKenneyd4c08f22011-06-25 06:36:56 -0700235 trace_rcu_preempt_task(rdp->rsp->name,
236 t->pid,
237 (rnp->qsmask & rdp->grpmask)
238 ? rnp->gpnum
239 : rnp->gpnum + 1);
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800240 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenney10f39bb2011-07-17 21:14:35 -0700241 } else if (t->rcu_read_lock_nesting < 0 &&
242 t->rcu_read_unlock_special) {
243
244 /*
245 * Complete exit from RCU read-side critical section on
246 * behalf of preempted instance of __rcu_read_unlock().
247 */
248 rcu_read_unlock_special(t);
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700249 }
250
251 /*
252 * Either we were not in an RCU read-side critical section to
253 * begin with, or we have now recorded that critical section
254 * globally. Either way, we can now note a quiescent state
255 * for this CPU. Again, if we were in an RCU read-side critical
256 * section, and if that critical section was blocking the current
257 * grace period, then the fact that the task has been enqueued
258 * means that we continue to block the current grace period.
259 */
Paul E. McKenneye7d88422009-09-18 09:50:18 -0700260 local_irq_save(flags);
Paul E. McKenneycba6d0d2012-07-02 07:08:42 -0700261 rcu_preempt_qs(cpu);
Paul E. McKenneye7d88422009-09-18 09:50:18 -0700262 local_irq_restore(flags);
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700263}
264
265/*
Paul E. McKenneyfc2219d2009-09-23 09:50:41 -0700266 * Check for preempted RCU readers blocking the current grace period
267 * for the specified rcu_node structure. If the caller needs a reliable
268 * answer, it must hold the rcu_node's ->lock.
269 */
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800270static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
Paul E. McKenneyfc2219d2009-09-23 09:50:41 -0700271{
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800272 return rnp->gp_tasks != NULL;
Paul E. McKenneyfc2219d2009-09-23 09:50:41 -0700273}
274
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800275/*
276 * Record a quiescent state for all tasks that were previously queued
277 * on the specified rcu_node structure and that were blocking the current
278 * RCU grace period. The caller must hold the specified rnp->lock with
279 * irqs disabled, and this lock is released upon return, but irqs remain
280 * disabled.
281 */
Paul E. McKenneyd3f6bad2009-12-02 12:10:13 -0800282static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800283 __releases(rnp->lock)
284{
285 unsigned long mask;
286 struct rcu_node *rnp_p;
287
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800288 if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800289 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800290 return; /* Still need more quiescent states! */
291 }
292
293 rnp_p = rnp->parent;
294 if (rnp_p == NULL) {
295 /*
296 * Either there is only one rcu_node in the tree,
297 * or tasks were kicked up to root rcu_node due to
298 * CPUs going offline.
299 */
Paul E. McKenneyd3f6bad2009-12-02 12:10:13 -0800300 rcu_report_qs_rsp(&rcu_preempt_state, flags);
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800301 return;
302 }
303
304 /* Report up the rest of the hierarchy. */
305 mask = rnp->grpmask;
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800306 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
307 raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */
Paul E. McKenney6303b9c2013-12-11 13:59:10 -0800308 smp_mb__after_unlock_lock();
Paul E. McKenneyd3f6bad2009-12-02 12:10:13 -0800309 rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags);
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800310}
311
312/*
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800313 * Advance a ->blkd_tasks-list pointer to the next entry, instead
314 * returning NULL if at the end of the list.
315 */
316static struct list_head *rcu_next_node_entry(struct task_struct *t,
317 struct rcu_node *rnp)
318{
319 struct list_head *np;
320
321 np = t->rcu_node_entry.next;
322 if (np == &rnp->blkd_tasks)
323 np = NULL;
324 return np;
325}
326
327/*
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800328 * Handle special cases during rcu_read_unlock(), such as needing to
329 * notify RCU core processing or task having blocked during the RCU
330 * read-side critical section.
331 */
Paul E. McKenney2a3fa842012-05-21 11:58:36 -0700332void rcu_read_unlock_special(struct task_struct *t)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700333{
334 int empty;
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800335 int empty_exp;
Paul E. McKenney389abd42011-09-21 14:41:37 -0700336 int empty_exp_now;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700337 unsigned long flags;
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800338 struct list_head *np;
Paul E. McKenney82e78d82011-08-04 07:55:34 -0700339#ifdef CONFIG_RCU_BOOST
Paul E. McKenneyabaa93d2014-06-12 13:30:25 -0700340 bool drop_boost_mutex = false;
Paul E. McKenney82e78d82011-08-04 07:55:34 -0700341#endif /* #ifdef CONFIG_RCU_BOOST */
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700342 struct rcu_node *rnp;
343 int special;
344
345 /* NMI handlers cannot block and cannot safely manipulate state. */
346 if (in_nmi())
347 return;
348
349 local_irq_save(flags);
350
351 /*
352 * If RCU core is waiting for this CPU to exit critical section,
353 * let it know that we have done so.
354 */
355 special = t->rcu_read_unlock_special;
356 if (special & RCU_READ_UNLOCK_NEED_QS) {
Paul E. McKenneyc3422be2009-09-13 09:15:10 -0700357 rcu_preempt_qs(smp_processor_id());
Lai Jiangshan79a62f92013-10-30 04:13:22 -0700358 if (!t->rcu_read_unlock_special) {
359 local_irq_restore(flags);
360 return;
361 }
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700362 }
363
Lai Jiangshan79a62f92013-10-30 04:13:22 -0700364 /* Hardware IRQ handlers cannot block, complain if they get here. */
365 if (WARN_ON_ONCE(in_irq() || in_serving_softirq())) {
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700366 local_irq_restore(flags);
367 return;
368 }
369
370 /* Clean up if blocked during RCU read-side critical section. */
371 if (special & RCU_READ_UNLOCK_BLOCKED) {
372 t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
373
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700374 /*
375 * Remove this task from the list it blocked on. The
376 * task can migrate while we acquire the lock, but at
377 * most one time. So at most two passes through loop.
378 */
379 for (;;) {
Paul E. McKenney86848962009-08-27 15:00:12 -0700380 rnp = t->rcu_blocked_node;
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800381 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
Paul E. McKenney6303b9c2013-12-11 13:59:10 -0800382 smp_mb__after_unlock_lock();
Paul E. McKenney86848962009-08-27 15:00:12 -0700383 if (rnp == t->rcu_blocked_node)
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700384 break;
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800385 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700386 }
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800387 empty = !rcu_preempt_blocked_readers_cgp(rnp);
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800388 empty_exp = !rcu_preempted_readers_exp(rnp);
389 smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800390 np = rcu_next_node_entry(t, rnp);
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700391 list_del_init(&t->rcu_node_entry);
Paul E. McKenney82e78d82011-08-04 07:55:34 -0700392 t->rcu_blocked_node = NULL;
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -0400393 trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
Paul E. McKenneyd4c08f22011-06-25 06:36:56 -0700394 rnp->gpnum, t->pid);
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800395 if (&t->rcu_node_entry == rnp->gp_tasks)
396 rnp->gp_tasks = np;
397 if (&t->rcu_node_entry == rnp->exp_tasks)
398 rnp->exp_tasks = np;
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800399#ifdef CONFIG_RCU_BOOST
400 if (&t->rcu_node_entry == rnp->boost_tasks)
401 rnp->boost_tasks = np;
Paul E. McKenneyabaa93d2014-06-12 13:30:25 -0700402 /* Snapshot ->boost_mtx ownership with rcu_node lock held. */
403 drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800404#endif /* #ifdef CONFIG_RCU_BOOST */
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700405
406 /*
407 * If this was the last task on the current list, and if
408 * we aren't waiting on any CPUs, report the quiescent state.
Paul E. McKenney389abd42011-09-21 14:41:37 -0700409 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
410 * so we must take a snapshot of the expedited state.
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700411 */
Paul E. McKenney389abd42011-09-21 14:41:37 -0700412 empty_exp_now = !rcu_preempted_readers_exp(rnp);
Paul E. McKenneyd4c08f22011-06-25 06:36:56 -0700413 if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) {
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -0400414 trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
Paul E. McKenneyd4c08f22011-06-25 06:36:56 -0700415 rnp->gpnum,
416 0, rnp->qsmask,
417 rnp->level,
418 rnp->grplo,
419 rnp->grphi,
420 !!rnp->gp_tasks);
Paul E. McKenneyd3f6bad2009-12-02 12:10:13 -0800421 rcu_report_unblock_qs_rnp(rnp, flags);
Paul E. McKenneyc701d5d2012-06-28 08:08:25 -0700422 } else {
Paul E. McKenneyd4c08f22011-06-25 06:36:56 -0700423 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenneyc701d5d2012-06-28 08:08:25 -0700424 }
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800425
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800426#ifdef CONFIG_RCU_BOOST
427 /* Unboost if we were boosted. */
Paul E. McKenneyabaa93d2014-06-12 13:30:25 -0700428 if (drop_boost_mutex) {
429 rt_mutex_unlock(&rnp->boost_mtx);
Paul E. McKenneydfeb9762014-06-10 16:31:55 -0700430 complete(&rnp->boost_completion);
431 }
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800432#endif /* #ifdef CONFIG_RCU_BOOST */
433
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800434 /*
435 * If this was the last task on the expedited lists,
436 * then we need to report up the rcu_node hierarchy.
437 */
Paul E. McKenney389abd42011-09-21 14:41:37 -0700438 if (!empty_exp && empty_exp_now)
Thomas Gleixnerb40d2932011-10-22 07:12:34 -0700439 rcu_report_exp_rnp(&rcu_preempt_state, rnp, true);
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800440 } else {
441 local_irq_restore(flags);
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700442 }
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700443}
444
Paul E. McKenney1ed509a2010-02-22 17:05:05 -0800445#ifdef CONFIG_RCU_CPU_STALL_VERBOSE
446
447/*
448 * Dump detailed information for all tasks blocking the current RCU
449 * grace period on the specified rcu_node structure.
450 */
451static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
452{
453 unsigned long flags;
Paul E. McKenney1ed509a2010-02-22 17:05:05 -0800454 struct task_struct *t;
455
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800456 raw_spin_lock_irqsave(&rnp->lock, flags);
Paul E. McKenney5fd4dc02012-08-10 16:00:11 -0700457 if (!rcu_preempt_blocked_readers_cgp(rnp)) {
458 raw_spin_unlock_irqrestore(&rnp->lock, flags);
459 return;
460 }
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800461 t = list_entry(rnp->gp_tasks,
462 struct task_struct, rcu_node_entry);
463 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
464 sched_show_task(t);
465 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenney1ed509a2010-02-22 17:05:05 -0800466}
467
468/*
469 * Dump detailed information for all tasks blocking the current RCU
470 * grace period.
471 */
472static void rcu_print_detail_task_stall(struct rcu_state *rsp)
473{
474 struct rcu_node *rnp = rcu_get_root(rsp);
475
476 rcu_print_detail_task_stall_rnp(rnp);
477 rcu_for_each_leaf_node(rsp, rnp)
478 rcu_print_detail_task_stall_rnp(rnp);
479}
480
481#else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
482
483static void rcu_print_detail_task_stall(struct rcu_state *rsp)
484{
485}
486
487#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
488
Paul E. McKenneya858af22012-01-16 13:29:10 -0800489#ifdef CONFIG_RCU_CPU_STALL_INFO
490
491static void rcu_print_task_stall_begin(struct rcu_node *rnp)
492{
Paul E. McKenneyefc151c2013-03-18 16:24:11 -0700493 pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
Paul E. McKenneya858af22012-01-16 13:29:10 -0800494 rnp->level, rnp->grplo, rnp->grphi);
495}
496
497static void rcu_print_task_stall_end(void)
498{
Paul E. McKenneyefc151c2013-03-18 16:24:11 -0700499 pr_cont("\n");
Paul E. McKenneya858af22012-01-16 13:29:10 -0800500}
501
502#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
503
504static void rcu_print_task_stall_begin(struct rcu_node *rnp)
505{
506}
507
508static void rcu_print_task_stall_end(void)
509{
510}
511
512#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
513
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700514/*
515 * Scan the current list of tasks blocked within RCU read-side critical
516 * sections, printing out the tid of each.
517 */
Paul E. McKenney9bc8b552011-08-13 13:31:47 -0700518static int rcu_print_task_stall(struct rcu_node *rnp)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700519{
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700520 struct task_struct *t;
Paul E. McKenney9bc8b552011-08-13 13:31:47 -0700521 int ndetected = 0;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700522
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800523 if (!rcu_preempt_blocked_readers_cgp(rnp))
Paul E. McKenney9bc8b552011-08-13 13:31:47 -0700524 return 0;
Paul E. McKenneya858af22012-01-16 13:29:10 -0800525 rcu_print_task_stall_begin(rnp);
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800526 t = list_entry(rnp->gp_tasks,
527 struct task_struct, rcu_node_entry);
Paul E. McKenney9bc8b552011-08-13 13:31:47 -0700528 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
Paul E. McKenneyefc151c2013-03-18 16:24:11 -0700529 pr_cont(" P%d", t->pid);
Paul E. McKenney9bc8b552011-08-13 13:31:47 -0700530 ndetected++;
531 }
Paul E. McKenneya858af22012-01-16 13:29:10 -0800532 rcu_print_task_stall_end();
Paul E. McKenney9bc8b552011-08-13 13:31:47 -0700533 return ndetected;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700534}
535
Paul E. McKenney53d84e02010-08-10 14:28:53 -0700536/*
Paul E. McKenneyb0e165c2009-09-13 09:15:09 -0700537 * Check that the list of blocked tasks for the newly completed grace
538 * period is in fact empty. It is a serious bug to complete a grace
539 * period that still has RCU readers blocked! This function must be
540 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
541 * must be held by the caller.
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800542 *
543 * Also, if there are blocked tasks on the list, they automatically
544 * block the newly created grace period, so set up ->gp_tasks accordingly.
Paul E. McKenneyb0e165c2009-09-13 09:15:09 -0700545 */
546static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
547{
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800548 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800549 if (!list_empty(&rnp->blkd_tasks))
550 rnp->gp_tasks = rnp->blkd_tasks.next;
Paul E. McKenney28ecd582009-09-18 09:50:17 -0700551 WARN_ON_ONCE(rnp->qsmask);
Paul E. McKenneyb0e165c2009-09-13 09:15:09 -0700552}
553
Paul E. McKenney33f76142009-08-24 09:42:01 -0700554#ifdef CONFIG_HOTPLUG_CPU
555
556/*
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700557 * Handle tasklist migration for case in which all CPUs covered by the
558 * specified rcu_node have gone offline. Move them up to the root
559 * rcu_node. The reason for not just moving them to the immediate
560 * parent is to remove the need for rcu_read_unlock_special() to
561 * make more than two attempts to acquire the target rcu_node's lock.
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800562 * Returns true if there were tasks blocking the current RCU grace
563 * period.
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700564 *
Paul E. McKenney237c80c2009-10-15 09:26:14 -0700565 * Returns 1 if there was previously a task blocking the current grace
566 * period on the specified rcu_node structure.
567 *
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700568 * The caller must hold rnp->lock with irqs disabled.
569 */
Paul E. McKenney237c80c2009-10-15 09:26:14 -0700570static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
571 struct rcu_node *rnp,
572 struct rcu_data *rdp)
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700573{
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700574 struct list_head *lp;
575 struct list_head *lp_root;
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800576 int retval = 0;
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700577 struct rcu_node *rnp_root = rcu_get_root(rsp);
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800578 struct task_struct *t;
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700579
Paul E. McKenney86848962009-08-27 15:00:12 -0700580 if (rnp == rnp_root) {
581 WARN_ONCE(1, "Last CPU thought to be offlined?");
Paul E. McKenney237c80c2009-10-15 09:26:14 -0700582 return 0; /* Shouldn't happen: at least one CPU online. */
Paul E. McKenney86848962009-08-27 15:00:12 -0700583 }
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800584
585 /* If we are on an internal node, complain bitterly. */
586 WARN_ON_ONCE(rnp != rdp->mynode);
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700587
588 /*
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800589 * Move tasks up to root rcu_node. Don't try to get fancy for
590 * this corner-case operation -- just put this node's tasks
591 * at the head of the root node's list, and update the root node's
592 * ->gp_tasks and ->exp_tasks pointers to those of this node's,
593 * if non-NULL. This might result in waiting for more tasks than
594 * absolutely necessary, but this is a good performance/complexity
595 * tradeoff.
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700596 */
Paul E. McKenney2036d942012-01-30 17:02:47 -0800597 if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0)
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800598 retval |= RCU_OFL_TASKS_NORM_GP;
599 if (rcu_preempted_readers_exp(rnp))
600 retval |= RCU_OFL_TASKS_EXP_GP;
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800601 lp = &rnp->blkd_tasks;
602 lp_root = &rnp_root->blkd_tasks;
603 while (!list_empty(lp)) {
604 t = list_entry(lp->next, typeof(*t), rcu_node_entry);
605 raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
Paul E. McKenney6303b9c2013-12-11 13:59:10 -0800606 smp_mb__after_unlock_lock();
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800607 list_del(&t->rcu_node_entry);
608 t->rcu_blocked_node = rnp_root;
609 list_add(&t->rcu_node_entry, lp_root);
610 if (&t->rcu_node_entry == rnp->gp_tasks)
611 rnp_root->gp_tasks = rnp->gp_tasks;
612 if (&t->rcu_node_entry == rnp->exp_tasks)
613 rnp_root->exp_tasks = rnp->exp_tasks;
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800614#ifdef CONFIG_RCU_BOOST
615 if (&t->rcu_node_entry == rnp->boost_tasks)
616 rnp_root->boost_tasks = rnp->boost_tasks;
617#endif /* #ifdef CONFIG_RCU_BOOST */
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800618 raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700619 }
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800620
Paul E. McKenney1e3fd2b2012-07-27 13:41:47 -0700621 rnp->gp_tasks = NULL;
622 rnp->exp_tasks = NULL;
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800623#ifdef CONFIG_RCU_BOOST
Paul E. McKenney1e3fd2b2012-07-27 13:41:47 -0700624 rnp->boost_tasks = NULL;
Paul E. McKenney5cc900c2012-07-31 14:09:49 -0700625 /*
626 * In case root is being boosted and leaf was not. Make sure
627 * that we boost the tasks blocking the current grace period
628 * in this case.
629 */
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800630 raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
Paul E. McKenney6303b9c2013-12-11 13:59:10 -0800631 smp_mb__after_unlock_lock();
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800632 if (rnp_root->boost_tasks != NULL &&
Paul E. McKenney5cc900c2012-07-31 14:09:49 -0700633 rnp_root->boost_tasks != rnp_root->gp_tasks &&
634 rnp_root->boost_tasks != rnp_root->exp_tasks)
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800635 rnp_root->boost_tasks = rnp_root->gp_tasks;
636 raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
637#endif /* #ifdef CONFIG_RCU_BOOST */
638
Paul E. McKenney237c80c2009-10-15 09:26:14 -0700639 return retval;
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700640}
641
Paul E. McKenneye5601402012-01-07 11:03:57 -0800642#endif /* #ifdef CONFIG_HOTPLUG_CPU */
643
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700644/*
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700645 * Check for a quiescent state from the current CPU. When a task blocks,
646 * the task is recorded in the corresponding CPU's rcu_node structure,
647 * which is checked elsewhere.
648 *
649 * Caller must disable hard irqs.
650 */
651static void rcu_preempt_check_callbacks(int cpu)
652{
653 struct task_struct *t = current;
654
655 if (t->rcu_read_lock_nesting == 0) {
Paul E. McKenneyc3422be2009-09-13 09:15:10 -0700656 rcu_preempt_qs(cpu);
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700657 return;
658 }
Paul E. McKenney10f39bb2011-07-17 21:14:35 -0700659 if (t->rcu_read_lock_nesting > 0 &&
660 per_cpu(rcu_preempt_data, cpu).qs_pending)
Paul E. McKenneyc3422be2009-09-13 09:15:10 -0700661 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700662}
663
Paul E. McKenneya46e0892011-06-15 15:47:09 -0700664#ifdef CONFIG_RCU_BOOST
665
Shaohua Li09223372011-06-14 13:26:25 +0800666static void rcu_preempt_do_callbacks(void)
667{
Christoph Lameterc9d4b0a2013-08-31 13:34:10 -0700668 rcu_do_batch(&rcu_preempt_state, this_cpu_ptr(&rcu_preempt_data));
Shaohua Li09223372011-06-14 13:26:25 +0800669}
670
Paul E. McKenneya46e0892011-06-15 15:47:09 -0700671#endif /* #ifdef CONFIG_RCU_BOOST */
672
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700673/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800674 * Queue a preemptible-RCU callback for invocation after a grace period.
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700675 */
676void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
677{
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -0700678 __call_rcu(head, func, &rcu_preempt_state, -1, 0);
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700679}
680EXPORT_SYMBOL_GPL(call_rcu);
681
Paul E. McKenney6ebb2372009-11-22 08:53:50 -0800682/**
683 * synchronize_rcu - wait until a grace period has elapsed.
684 *
685 * Control will return to the caller some time after a full grace
686 * period has elapsed, in other words after all currently executing RCU
Paul E. McKenney77d84852010-07-08 17:38:59 -0700687 * read-side critical sections have completed. Note, however, that
688 * upon return from synchronize_rcu(), the caller might well be executing
689 * concurrently with new RCU read-side critical sections that began while
690 * synchronize_rcu() was waiting. RCU read-side critical sections are
691 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
Paul E. McKenneyf0a0e6f2012-10-23 13:47:01 -0700692 *
693 * See the description of synchronize_sched() for more detailed information
694 * on memory ordering guarantees.
Paul E. McKenney6ebb2372009-11-22 08:53:50 -0800695 */
696void synchronize_rcu(void)
697{
Paul E. McKenneyfe15d702012-01-04 13:30:33 -0800698 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
699 !lock_is_held(&rcu_lock_map) &&
700 !lock_is_held(&rcu_sched_lock_map),
701 "Illegal synchronize_rcu() in RCU read-side critical section");
Paul E. McKenney6ebb2372009-11-22 08:53:50 -0800702 if (!rcu_scheduler_active)
703 return;
Antti P Miettinen3705b882012-10-05 09:59:15 +0300704 if (rcu_expedited)
705 synchronize_rcu_expedited();
706 else
707 wait_rcu_gp(call_rcu);
Paul E. McKenney6ebb2372009-11-22 08:53:50 -0800708}
709EXPORT_SYMBOL_GPL(synchronize_rcu);
710
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800711static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
Paul E. McKenneybcfa57c2012-07-23 16:03:51 -0700712static unsigned long sync_rcu_preempt_exp_count;
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800713static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
714
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700715/*
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800716 * Return non-zero if there are any tasks in RCU read-side critical
717 * sections blocking the current preemptible-RCU expedited grace period.
718 * If there is no preemptible-RCU expedited grace period currently in
719 * progress, returns zero unconditionally.
720 */
721static int rcu_preempted_readers_exp(struct rcu_node *rnp)
722{
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800723 return rnp->exp_tasks != NULL;
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800724}
725
726/*
727 * return non-zero if there is no RCU expedited grace period in progress
728 * for the specified rcu_node structure, in other words, if all CPUs and
729 * tasks covered by the specified rcu_node structure have done their bit
730 * for the current expedited grace period. Works only for preemptible
731 * RCU -- other RCU implementation use other means.
732 *
733 * Caller must hold sync_rcu_preempt_exp_mutex.
734 */
735static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
736{
737 return !rcu_preempted_readers_exp(rnp) &&
738 ACCESS_ONCE(rnp->expmask) == 0;
739}
740
741/*
742 * Report the exit from RCU read-side critical section for the last task
743 * that queued itself during or before the current expedited preemptible-RCU
744 * grace period. This event is reported either to the rcu_node structure on
745 * which the task was queued or to one of that rcu_node structure's ancestors,
746 * recursively up the tree. (Calm down, calm down, we do the recursion
747 * iteratively!)
748 *
Thomas Gleixnerb40d2932011-10-22 07:12:34 -0700749 * Most callers will set the "wake" flag, but the task initiating the
750 * expedited grace period need not wake itself.
751 *
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800752 * Caller must hold sync_rcu_preempt_exp_mutex.
753 */
Thomas Gleixnerb40d2932011-10-22 07:12:34 -0700754static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
755 bool wake)
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800756{
757 unsigned long flags;
758 unsigned long mask;
759
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800760 raw_spin_lock_irqsave(&rnp->lock, flags);
Paul E. McKenney6303b9c2013-12-11 13:59:10 -0800761 smp_mb__after_unlock_lock();
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800762 for (;;) {
Paul E. McKenney131906b2011-07-17 02:05:49 -0700763 if (!sync_rcu_preempt_exp_done(rnp)) {
764 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800765 break;
Paul E. McKenney131906b2011-07-17 02:05:49 -0700766 }
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800767 if (rnp->parent == NULL) {
Paul E. McKenney131906b2011-07-17 02:05:49 -0700768 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenney78e4bc32013-09-24 15:04:06 -0700769 if (wake) {
770 smp_mb(); /* EGP done before wake_up(). */
Thomas Gleixnerb40d2932011-10-22 07:12:34 -0700771 wake_up(&sync_rcu_preempt_exp_wq);
Paul E. McKenney78e4bc32013-09-24 15:04:06 -0700772 }
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800773 break;
774 }
775 mask = rnp->grpmask;
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800776 raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800777 rnp = rnp->parent;
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800778 raw_spin_lock(&rnp->lock); /* irqs already disabled */
Paul E. McKenney6303b9c2013-12-11 13:59:10 -0800779 smp_mb__after_unlock_lock();
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800780 rnp->expmask &= ~mask;
781 }
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800782}
783
784/*
785 * Snapshot the tasks blocking the newly started preemptible-RCU expedited
786 * grace period for the specified rcu_node structure. If there are no such
787 * tasks, report it up the rcu_node hierarchy.
788 *
Paul E. McKenney7b2e6012012-10-08 10:54:03 -0700789 * Caller must hold sync_rcu_preempt_exp_mutex and must exclude
790 * CPU hotplug operations.
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800791 */
792static void
793sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
794{
Paul E. McKenney1217ed12011-05-04 21:43:49 -0700795 unsigned long flags;
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800796 int must_wait = 0;
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800797
Paul E. McKenney1217ed12011-05-04 21:43:49 -0700798 raw_spin_lock_irqsave(&rnp->lock, flags);
Paul E. McKenney6303b9c2013-12-11 13:59:10 -0800799 smp_mb__after_unlock_lock();
Paul E. McKenneyc701d5d2012-06-28 08:08:25 -0700800 if (list_empty(&rnp->blkd_tasks)) {
Paul E. McKenney1217ed12011-05-04 21:43:49 -0700801 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenneyc701d5d2012-06-28 08:08:25 -0700802 } else {
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800803 rnp->exp_tasks = rnp->blkd_tasks.next;
Paul E. McKenney1217ed12011-05-04 21:43:49 -0700804 rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800805 must_wait = 1;
806 }
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800807 if (!must_wait)
Thomas Gleixnerb40d2932011-10-22 07:12:34 -0700808 rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800809}
810
Paul E. McKenney236fefa2012-01-31 14:00:41 -0800811/**
812 * synchronize_rcu_expedited - Brute-force RCU grace period
813 *
814 * Wait for an RCU-preempt grace period, but expedite it. The basic
815 * idea is to invoke synchronize_sched_expedited() to push all the tasks to
816 * the ->blkd_tasks lists and wait for this list to drain. This consumes
817 * significant time on all CPUs and is unfriendly to real-time workloads,
818 * so is thus not recommended for any sort of common-case code.
819 * In fact, if you are using synchronize_rcu_expedited() in a loop,
820 * please restructure your code to batch your updates, and then Use a
821 * single synchronize_rcu() instead.
822 *
823 * Note that it is illegal to call this function while holding any lock
824 * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
825 * to call this function from a CPU-hotplug notifier. Failing to observe
826 * these restriction will result in deadlock.
Paul E. McKenney019129d52009-10-14 10:15:56 -0700827 */
828void synchronize_rcu_expedited(void)
829{
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800830 unsigned long flags;
831 struct rcu_node *rnp;
832 struct rcu_state *rsp = &rcu_preempt_state;
Paul E. McKenneybcfa57c2012-07-23 16:03:51 -0700833 unsigned long snap;
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800834 int trycount = 0;
835
836 smp_mb(); /* Caller's modifications seen first by other CPUs. */
837 snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
838 smp_mb(); /* Above access cannot bleed into critical section. */
839
840 /*
Paul E. McKenney1943c892012-07-30 17:19:25 -0700841 * Block CPU-hotplug operations. This means that any CPU-hotplug
842 * operation that finds an rcu_node structure with tasks in the
843 * process of being boosted will know that all tasks blocking
844 * this expedited grace period will already be in the process of
845 * being boosted. This simplifies the process of moving tasks
846 * from leaf to root rcu_node structures.
847 */
848 get_online_cpus();
849
850 /*
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800851 * Acquire lock, falling back to synchronize_rcu() if too many
852 * lock-acquisition failures. Of course, if someone does the
853 * expedited grace period for us, just leave.
854 */
855 while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
Paul E. McKenney1943c892012-07-30 17:19:25 -0700856 if (ULONG_CMP_LT(snap,
857 ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
858 put_online_cpus();
859 goto mb_ret; /* Others did our work for us. */
860 }
Paul E. McKenneyc701d5d2012-06-28 08:08:25 -0700861 if (trycount++ < 10) {
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800862 udelay(trycount * num_online_cpus());
Paul E. McKenneyc701d5d2012-06-28 08:08:25 -0700863 } else {
Paul E. McKenney1943c892012-07-30 17:19:25 -0700864 put_online_cpus();
Antti P Miettinen3705b882012-10-05 09:59:15 +0300865 wait_rcu_gp(call_rcu);
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800866 return;
867 }
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800868 }
Paul E. McKenney1943c892012-07-30 17:19:25 -0700869 if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
870 put_online_cpus();
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800871 goto unlock_mb_ret; /* Others did our work for us. */
Paul E. McKenney1943c892012-07-30 17:19:25 -0700872 }
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800873
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800874 /* force all RCU readers onto ->blkd_tasks lists. */
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800875 synchronize_sched_expedited();
876
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800877 /* Initialize ->expmask for all non-leaf rcu_node structures. */
878 rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
Paul E. McKenney1943c892012-07-30 17:19:25 -0700879 raw_spin_lock_irqsave(&rnp->lock, flags);
Paul E. McKenney6303b9c2013-12-11 13:59:10 -0800880 smp_mb__after_unlock_lock();
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800881 rnp->expmask = rnp->qsmaskinit;
Paul E. McKenney1943c892012-07-30 17:19:25 -0700882 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800883 }
884
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800885 /* Snapshot current state of ->blkd_tasks lists. */
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800886 rcu_for_each_leaf_node(rsp, rnp)
887 sync_rcu_preempt_exp_init(rsp, rnp);
888 if (NUM_RCU_NODES > 1)
889 sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));
890
Paul E. McKenney1943c892012-07-30 17:19:25 -0700891 put_online_cpus();
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800892
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800893 /* Wait for snapshotted ->blkd_tasks lists to drain. */
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800894 rnp = rcu_get_root(rsp);
895 wait_event(sync_rcu_preempt_exp_wq,
896 sync_rcu_preempt_exp_done(rnp));
897
898 /* Clean up and exit. */
899 smp_mb(); /* ensure expedited GP seen before counter increment. */
900 ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
901unlock_mb_ret:
902 mutex_unlock(&sync_rcu_preempt_exp_mutex);
903mb_ret:
904 smp_mb(); /* ensure subsequent action seen after grace period. */
Paul E. McKenney019129d52009-10-14 10:15:56 -0700905}
906EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
907
Paul E. McKenneye74f4c42009-10-06 21:48:17 -0700908/**
909 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
Paul E. McKenneyf0a0e6f2012-10-23 13:47:01 -0700910 *
911 * Note that this primitive does not necessarily wait for an RCU grace period
912 * to complete. For example, if there are no RCU callbacks queued anywhere
913 * in the system, then rcu_barrier() is within its rights to return
914 * immediately, without waiting for anything, much less an RCU grace period.
Paul E. McKenneye74f4c42009-10-06 21:48:17 -0700915 */
916void rcu_barrier(void)
917{
Paul E. McKenney037b64e2012-05-28 23:26:01 -0700918 _rcu_barrier(&rcu_preempt_state);
Paul E. McKenneye74f4c42009-10-06 21:48:17 -0700919}
920EXPORT_SYMBOL_GPL(rcu_barrier);
921
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700922/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800923 * Initialize preemptible RCU's state structures.
Paul E. McKenney1eba8f82009-09-23 09:50:42 -0700924 */
925static void __init __rcu_init_preempt(void)
926{
Lai Jiangshan394f99a2010-06-28 16:25:04 +0800927 rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
Paul E. McKenney1eba8f82009-09-23 09:50:42 -0700928}
929
Paul E. McKenney2439b692013-04-11 10:15:52 -0700930/*
931 * Check for a task exiting while in a preemptible-RCU read-side
932 * critical section, clean up if so. No need to issue warnings,
933 * as debug_check_no_locks_held() already does this if lockdep
934 * is enabled.
935 */
936void exit_rcu(void)
937{
938 struct task_struct *t = current;
939
940 if (likely(list_empty(&current->rcu_node_entry)))
941 return;
942 t->rcu_read_lock_nesting = 1;
943 barrier();
944 t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
945 __rcu_read_unlock();
946}
947
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700948#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
949
Uma Sharmae5341652014-03-23 22:32:09 -0700950static struct rcu_state *rcu_state_p = &rcu_sched_state;
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800951
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700952/*
953 * Tell them what RCU they are running.
954 */
Paul E. McKenney0e0fc1c2009-11-11 11:28:06 -0800955static void __init rcu_bootup_announce(void)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700956{
Paul E. McKenneyefc151c2013-03-18 16:24:11 -0700957 pr_info("Hierarchical RCU implementation.\n");
Paul E. McKenney26845c22010-04-13 14:19:23 -0700958 rcu_bootup_announce_oddness();
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700959}
960
961/*
962 * Return the number of RCU batches processed thus far for debug & stats.
963 */
964long rcu_batches_completed(void)
965{
966 return rcu_batches_completed_sched();
967}
968EXPORT_SYMBOL_GPL(rcu_batches_completed);
969
970/*
Paul E. McKenneycba6d0d2012-07-02 07:08:42 -0700971 * Because preemptible RCU does not exist, we never have to check for
972 * CPUs being in quiescent states.
973 */
974static void rcu_preempt_note_context_switch(int cpu)
975{
976}
977
978/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800979 * Because preemptible RCU does not exist, there are never any preempted
Paul E. McKenneyfc2219d2009-09-23 09:50:41 -0700980 * RCU readers.
981 */
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800982static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
Paul E. McKenneyfc2219d2009-09-23 09:50:41 -0700983{
984 return 0;
985}
986
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800987#ifdef CONFIG_HOTPLUG_CPU
988
989/* Because preemptible RCU does not exist, no quieting of tasks. */
Paul E. McKenneyd3f6bad2009-12-02 12:10:13 -0800990static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800991{
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800992 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800993}
994
995#endif /* #ifdef CONFIG_HOTPLUG_CPU */
996
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700997/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800998 * Because preemptible RCU does not exist, we never have to check for
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700999 * tasks blocked within RCU read-side critical sections.
1000 */
Paul E. McKenney1ed509a2010-02-22 17:05:05 -08001001static void rcu_print_detail_task_stall(struct rcu_state *rsp)
1002{
1003}
1004
1005/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -08001006 * Because preemptible RCU does not exist, we never have to check for
Paul E. McKenney1ed509a2010-02-22 17:05:05 -08001007 * tasks blocked within RCU read-side critical sections.
1008 */
Paul E. McKenney9bc8b552011-08-13 13:31:47 -07001009static int rcu_print_task_stall(struct rcu_node *rnp)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -07001010{
Paul E. McKenney9bc8b552011-08-13 13:31:47 -07001011 return 0;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -07001012}
1013
Paul E. McKenney53d84e02010-08-10 14:28:53 -07001014/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -08001015 * Because there is no preemptible RCU, there can be no readers blocked,
Paul E. McKenney49e29122009-09-18 09:50:19 -07001016 * so there is no need to check for blocked tasks. So check only for
1017 * bogus qsmask values.
Paul E. McKenneyb0e165c2009-09-13 09:15:09 -07001018 */
1019static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
1020{
Paul E. McKenney49e29122009-09-18 09:50:19 -07001021 WARN_ON_ONCE(rnp->qsmask);
Paul E. McKenneyb0e165c2009-09-13 09:15:09 -07001022}
1023
Paul E. McKenney33f76142009-08-24 09:42:01 -07001024#ifdef CONFIG_HOTPLUG_CPU
1025
1026/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -08001027 * Because preemptible RCU does not exist, it never needs to migrate
Paul E. McKenney237c80c2009-10-15 09:26:14 -07001028 * tasks that were blocked within RCU read-side critical sections, and
1029 * such non-existent tasks cannot possibly have been blocking the current
1030 * grace period.
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -07001031 */
Paul E. McKenney237c80c2009-10-15 09:26:14 -07001032static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
1033 struct rcu_node *rnp,
1034 struct rcu_data *rdp)
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -07001035{
Paul E. McKenney237c80c2009-10-15 09:26:14 -07001036 return 0;
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -07001037}
1038
Paul E. McKenneye5601402012-01-07 11:03:57 -08001039#endif /* #ifdef CONFIG_HOTPLUG_CPU */
1040
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -07001041/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -08001042 * Because preemptible RCU does not exist, it never has any callbacks
Paul E. McKenneyf41d9112009-08-22 13:56:52 -07001043 * to check.
1044 */
Paul E. McKenney1eba8f82009-09-23 09:50:42 -07001045static void rcu_preempt_check_callbacks(int cpu)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -07001046{
1047}
1048
1049/*
Paul E. McKenney019129d52009-10-14 10:15:56 -07001050 * Wait for an rcu-preempt grace period, but make it happen quickly.
Paul E. McKenney6cc68792011-03-02 13:15:15 -08001051 * But because preemptible RCU does not exist, map to rcu-sched.
Paul E. McKenney019129d52009-10-14 10:15:56 -07001052 */
1053void synchronize_rcu_expedited(void)
1054{
1055 synchronize_sched_expedited();
1056}
1057EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
1058
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -08001059#ifdef CONFIG_HOTPLUG_CPU
1060
1061/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -08001062 * Because preemptible RCU does not exist, there is never any need to
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -08001063 * report on tasks preempted in RCU read-side critical sections during
1064 * expedited RCU grace periods.
1065 */
Thomas Gleixnerb40d2932011-10-22 07:12:34 -07001066static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
1067 bool wake)
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -08001068{
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -08001069}
1070
1071#endif /* #ifdef CONFIG_HOTPLUG_CPU */
1072
Paul E. McKenney019129d52009-10-14 10:15:56 -07001073/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -08001074 * Because preemptible RCU does not exist, rcu_barrier() is just
Paul E. McKenneye74f4c42009-10-06 21:48:17 -07001075 * another name for rcu_barrier_sched().
1076 */
1077void rcu_barrier(void)
1078{
1079 rcu_barrier_sched();
1080}
1081EXPORT_SYMBOL_GPL(rcu_barrier);
1082
1083/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -08001084 * Because preemptible RCU does not exist, it need not be initialized.
Paul E. McKenney1eba8f82009-09-23 09:50:42 -07001085 */
1086static void __init __rcu_init_preempt(void)
1087{
1088}
1089
Paul E. McKenney2439b692013-04-11 10:15:52 -07001090/*
1091 * Because preemptible RCU does not exist, tasks cannot possibly exit
1092 * while in preemptible RCU read-side critical sections.
1093 */
1094void exit_rcu(void)
1095{
1096}
1097
Paul E. McKenneyf41d9112009-08-22 13:56:52 -07001098#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001099
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001100#ifdef CONFIG_RCU_BOOST
1101
Peter Zijlstra1696a8b2013-10-31 18:18:19 +01001102#include "../locking/rtmutex_common.h"
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001103
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -08001104#ifdef CONFIG_RCU_TRACE
1105
1106static void rcu_initiate_boost_trace(struct rcu_node *rnp)
1107{
1108 if (list_empty(&rnp->blkd_tasks))
1109 rnp->n_balk_blkd_tasks++;
1110 else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
1111 rnp->n_balk_exp_gp_tasks++;
1112 else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL)
1113 rnp->n_balk_boost_tasks++;
1114 else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
1115 rnp->n_balk_notblocked++;
1116 else if (rnp->gp_tasks != NULL &&
Paul E. McKenneya9f47932011-05-02 03:46:10 -07001117 ULONG_CMP_LT(jiffies, rnp->boost_time))
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -08001118 rnp->n_balk_notyet++;
1119 else
1120 rnp->n_balk_nos++;
1121}
1122
1123#else /* #ifdef CONFIG_RCU_TRACE */
1124
1125static void rcu_initiate_boost_trace(struct rcu_node *rnp)
1126{
1127}
1128
1129#endif /* #else #ifdef CONFIG_RCU_TRACE */
1130
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001131static void rcu_wake_cond(struct task_struct *t, int status)
1132{
1133 /*
1134 * If the thread is yielding, only wake it when this
1135 * is invoked from idle
1136 */
1137 if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
1138 wake_up_process(t);
1139}
1140
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001141/*
1142 * Carry out RCU priority boosting on the task indicated by ->exp_tasks
1143 * or ->boost_tasks, advancing the pointer to the next task in the
1144 * ->blkd_tasks list.
1145 *
1146 * Note that irqs must be enabled: boosting the task can block.
1147 * Returns 1 if there are more tasks needing to be boosted.
1148 */
1149static int rcu_boost(struct rcu_node *rnp)
1150{
1151 unsigned long flags;
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001152 struct task_struct *t;
1153 struct list_head *tb;
1154
1155 if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL)
1156 return 0; /* Nothing left to boost. */
1157
1158 raw_spin_lock_irqsave(&rnp->lock, flags);
Paul E. McKenney6303b9c2013-12-11 13:59:10 -08001159 smp_mb__after_unlock_lock();
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001160
1161 /*
1162 * Recheck under the lock: all tasks in need of boosting
1163 * might exit their RCU read-side critical sections on their own.
1164 */
1165 if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
1166 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1167 return 0;
1168 }
1169
1170 /*
1171 * Preferentially boost tasks blocking expedited grace periods.
1172 * This cannot starve the normal grace periods because a second
1173 * expedited grace period must boost all blocked tasks, including
1174 * those blocking the pre-existing normal grace period.
1175 */
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -08001176 if (rnp->exp_tasks != NULL) {
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001177 tb = rnp->exp_tasks;
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -08001178 rnp->n_exp_boosts++;
1179 } else {
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001180 tb = rnp->boost_tasks;
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -08001181 rnp->n_normal_boosts++;
1182 }
1183 rnp->n_tasks_boosted++;
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001184
1185 /*
1186 * We boost task t by manufacturing an rt_mutex that appears to
1187 * be held by task t. We leave a pointer to that rt_mutex where
1188 * task t can find it, and task t will release the mutex when it
1189 * exits its outermost RCU read-side critical section. Then
1190 * simply acquiring this artificial rt_mutex will boost task
1191 * t's priority. (Thanks to tglx for suggesting this approach!)
1192 *
1193 * Note that task t must acquire rnp->lock to remove itself from
1194 * the ->blkd_tasks list, which it will do from exit() if from
1195 * nowhere else. We therefore are guaranteed that task t will
1196 * stay around at least until we drop rnp->lock. Note that
1197 * rnp->lock also resolves races between our priority boosting
1198 * and task t's exiting its outermost RCU read-side critical
1199 * section.
1200 */
1201 t = container_of(tb, struct task_struct, rcu_node_entry);
Paul E. McKenneyabaa93d2014-06-12 13:30:25 -07001202 rt_mutex_init_proxy_locked(&rnp->boost_mtx, t);
Paul E. McKenneydfeb9762014-06-10 16:31:55 -07001203 init_completion(&rnp->boost_completion);
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001204 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenneyabaa93d2014-06-12 13:30:25 -07001205 /* Lock only for side effect: boosts task t's priority. */
1206 rt_mutex_lock(&rnp->boost_mtx);
1207 rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001208
Paul E. McKenneyabaa93d2014-06-12 13:30:25 -07001209 /* Wait for boostee to be done w/boost_mtx before reinitializing. */
Paul E. McKenneydfeb9762014-06-10 16:31:55 -07001210 wait_for_completion(&rnp->boost_completion);
1211
Paul E. McKenney4f89b332011-12-09 14:43:47 -08001212 return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
1213 ACCESS_ONCE(rnp->boost_tasks) != NULL;
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001214}
1215
1216/*
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001217 * Priority-boosting kthread. One per leaf rcu_node and one for the
1218 * root rcu_node.
1219 */
1220static int rcu_boost_kthread(void *arg)
1221{
1222 struct rcu_node *rnp = (struct rcu_node *)arg;
1223 int spincnt = 0;
1224 int more2boost;
1225
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04001226 trace_rcu_utilization(TPS("Start boost kthread@init"));
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001227 for (;;) {
Paul E. McKenneyd71df902011-03-29 17:48:28 -07001228 rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04001229 trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
Peter Zijlstra08bca602011-05-20 16:06:29 -07001230 rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04001231 trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
Paul E. McKenneyd71df902011-03-29 17:48:28 -07001232 rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001233 more2boost = rcu_boost(rnp);
1234 if (more2boost)
1235 spincnt++;
1236 else
1237 spincnt = 0;
1238 if (spincnt > 10) {
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001239 rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04001240 trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001241 schedule_timeout_interruptible(2);
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04001242 trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001243 spincnt = 0;
1244 }
1245 }
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001246 /* NOTREACHED */
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04001247 trace_rcu_utilization(TPS("End boost kthread@notreached"));
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001248 return 0;
1249}
1250
1251/*
1252 * Check to see if it is time to start boosting RCU readers that are
1253 * blocking the current grace period, and, if so, tell the per-rcu_node
1254 * kthread to start boosting them. If there is an expedited grace
1255 * period in progress, it is always time to boost.
1256 *
Paul E. McKenneyb065a852012-08-01 15:57:54 -07001257 * The caller must hold rnp->lock, which this function releases.
1258 * The ->boost_kthread_task is immortal, so we don't need to worry
1259 * about it going away.
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001260 */
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001261static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001262{
1263 struct task_struct *t;
1264
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -08001265 if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
1266 rnp->n_balk_exp_gp_tasks++;
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001267 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001268 return;
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -08001269 }
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001270 if (rnp->exp_tasks != NULL ||
1271 (rnp->gp_tasks != NULL &&
1272 rnp->boost_tasks == NULL &&
1273 rnp->qsmask == 0 &&
1274 ULONG_CMP_GE(jiffies, rnp->boost_time))) {
1275 if (rnp->exp_tasks == NULL)
1276 rnp->boost_tasks = rnp->gp_tasks;
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001277 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001278 t = rnp->boost_kthread_task;
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001279 if (t)
1280 rcu_wake_cond(t, rnp->boost_kthread_status);
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001281 } else {
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -08001282 rcu_initiate_boost_trace(rnp);
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001283 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1284 }
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001285}
1286
Paul E. McKenney0f962a52011-04-14 12:13:53 -07001287/*
Paul E. McKenneya46e0892011-06-15 15:47:09 -07001288 * Wake up the per-CPU kthread to invoke RCU callbacks.
1289 */
1290static void invoke_rcu_callbacks_kthread(void)
1291{
1292 unsigned long flags;
1293
1294 local_irq_save(flags);
1295 __this_cpu_write(rcu_cpu_has_work, 1);
Shaohua Li1eb52122011-06-16 16:02:54 -07001296 if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001297 current != __this_cpu_read(rcu_cpu_kthread_task)) {
1298 rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
1299 __this_cpu_read(rcu_cpu_kthread_status));
1300 }
Paul E. McKenneya46e0892011-06-15 15:47:09 -07001301 local_irq_restore(flags);
1302}
1303
1304/*
Paul E. McKenneydff16722011-11-29 15:57:13 -08001305 * Is the current CPU running the RCU-callbacks kthread?
1306 * Caller must have preemption disabled.
1307 */
1308static bool rcu_is_callbacks_kthread(void)
1309{
Christoph Lameterc9d4b0a2013-08-31 13:34:10 -07001310 return __this_cpu_read(rcu_cpu_kthread_task) == current;
Paul E. McKenneydff16722011-11-29 15:57:13 -08001311}
1312
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001313#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1314
1315/*
1316 * Do priority-boost accounting for the start of a new grace period.
1317 */
1318static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1319{
1320 rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
1321}
1322
1323/*
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001324 * Create an RCU-boost kthread for the specified node if one does not
1325 * already exist. We only create this kthread for preemptible RCU.
1326 * Returns zero if all is well, a negated errno otherwise.
1327 */
Paul Gortmaker49fb4c62013-06-19 14:52:21 -04001328static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001329 struct rcu_node *rnp)
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001330{
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001331 int rnp_index = rnp - &rsp->node[0];
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001332 unsigned long flags;
1333 struct sched_param sp;
1334 struct task_struct *t;
1335
1336 if (&rcu_preempt_state != rsp)
1337 return 0;
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001338
1339 if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0)
1340 return 0;
1341
Paul E. McKenneya46e0892011-06-15 15:47:09 -07001342 rsp->boost = 1;
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001343 if (rnp->boost_kthread_task != NULL)
1344 return 0;
1345 t = kthread_create(rcu_boost_kthread, (void *)rnp,
Mike Galbraith5b61b0b2011-08-19 11:39:11 -07001346 "rcub/%d", rnp_index);
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001347 if (IS_ERR(t))
1348 return PTR_ERR(t);
1349 raw_spin_lock_irqsave(&rnp->lock, flags);
Paul E. McKenney6303b9c2013-12-11 13:59:10 -08001350 smp_mb__after_unlock_lock();
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001351 rnp->boost_kthread_task = t;
1352 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Mike Galbraith5b61b0b2011-08-19 11:39:11 -07001353 sp.sched_priority = RCU_BOOST_PRIO;
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001354 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
Paul E. McKenney9a432732011-05-30 20:38:55 -07001355 wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001356 return 0;
1357}
1358
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001359static void rcu_kthread_do_work(void)
1360{
Christoph Lameterc9d4b0a2013-08-31 13:34:10 -07001361 rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data));
1362 rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data));
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001363 rcu_preempt_do_callbacks();
1364}
1365
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001366static void rcu_cpu_kthread_setup(unsigned int cpu)
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001367{
1368 struct sched_param sp;
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001369
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001370 sp.sched_priority = RCU_KTHREAD_PRIO;
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001371 sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001372}
1373
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001374static void rcu_cpu_kthread_park(unsigned int cpu)
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001375{
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001376 per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
1377}
1378
1379static int rcu_cpu_kthread_should_run(unsigned int cpu)
1380{
Christoph Lameterc9d4b0a2013-08-31 13:34:10 -07001381 return __this_cpu_read(rcu_cpu_has_work);
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001382}
1383
1384/*
1385 * Per-CPU kernel thread that invokes RCU callbacks. This replaces the
Paul E. McKenneye0f23062011-06-21 01:29:39 -07001386 * RCU softirq used in flavors and configurations of RCU that do not
1387 * support RCU priority boosting.
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001388 */
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001389static void rcu_cpu_kthread(unsigned int cpu)
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001390{
Christoph Lameterc9d4b0a2013-08-31 13:34:10 -07001391 unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
1392 char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001393 int spincnt;
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001394
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001395 for (spincnt = 0; spincnt < 10; spincnt++) {
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04001396 trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001397 local_bh_disable();
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001398 *statusp = RCU_KTHREAD_RUNNING;
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001399 this_cpu_inc(rcu_cpu_kthread_loops);
1400 local_irq_disable();
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001401 work = *workp;
1402 *workp = 0;
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001403 local_irq_enable();
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001404 if (work)
1405 rcu_kthread_do_work();
1406 local_bh_enable();
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001407 if (*workp == 0) {
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04001408 trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001409 *statusp = RCU_KTHREAD_WAITING;
1410 return;
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001411 }
1412 }
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001413 *statusp = RCU_KTHREAD_YIELDING;
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04001414 trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001415 schedule_timeout_interruptible(2);
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04001416 trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001417 *statusp = RCU_KTHREAD_WAITING;
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001418}
1419
1420/*
1421 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1422 * served by the rcu_node in question. The CPU hotplug lock is still
1423 * held, so the value of rnp->qsmaskinit will be stable.
1424 *
1425 * We don't include outgoingcpu in the affinity set, use -1 if there is
1426 * no outgoing CPU. If there are no CPUs left in the affinity set,
1427 * this function allows the kthread to execute on any CPU.
1428 */
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001429static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001430{
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001431 struct task_struct *t = rnp->boost_kthread_task;
1432 unsigned long mask = rnp->qsmaskinit;
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001433 cpumask_var_t cm;
1434 int cpu;
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001435
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001436 if (!t)
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001437 return;
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001438 if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001439 return;
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001440 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
1441 if ((mask & 0x1) && cpu != outgoingcpu)
1442 cpumask_set_cpu(cpu, cm);
1443 if (cpumask_weight(cm) == 0) {
1444 cpumask_setall(cm);
1445 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
1446 cpumask_clear_cpu(cpu, cm);
1447 WARN_ON_ONCE(cpumask_weight(cm) == 0);
1448 }
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001449 set_cpus_allowed_ptr(t, cm);
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001450 free_cpumask_var(cm);
1451}
1452
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001453static struct smp_hotplug_thread rcu_cpu_thread_spec = {
1454 .store = &rcu_cpu_kthread_task,
1455 .thread_should_run = rcu_cpu_kthread_should_run,
1456 .thread_fn = rcu_cpu_kthread,
1457 .thread_comm = "rcuc/%u",
1458 .setup = rcu_cpu_kthread_setup,
1459 .park = rcu_cpu_kthread_park,
1460};
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001461
1462/*
1463 * Spawn all kthreads -- called as soon as the scheduler is running.
1464 */
1465static int __init rcu_spawn_kthreads(void)
1466{
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001467 struct rcu_node *rnp;
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001468 int cpu;
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001469
Paul E. McKenneyb0d30412011-07-10 15:57:35 -07001470 rcu_scheduler_fully_active = 1;
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001471 for_each_possible_cpu(cpu)
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001472 per_cpu(rcu_cpu_has_work, cpu) = 0;
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001473 BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
Uma Sharmae5341652014-03-23 22:32:09 -07001474 rnp = rcu_get_root(rcu_state_p);
1475 (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001476 if (NUM_RCU_NODES > 1) {
Uma Sharmae5341652014-03-23 22:32:09 -07001477 rcu_for_each_leaf_node(rcu_state_p, rnp)
1478 (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001479 }
1480 return 0;
1481}
1482early_initcall(rcu_spawn_kthreads);
1483
Paul Gortmaker49fb4c62013-06-19 14:52:21 -04001484static void rcu_prepare_kthreads(int cpu)
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001485{
Uma Sharmae5341652014-03-23 22:32:09 -07001486 struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001487 struct rcu_node *rnp = rdp->mynode;
1488
1489 /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
Paul E. McKenney62ab7072012-07-16 10:42:38 +00001490 if (rcu_scheduler_fully_active)
Uma Sharmae5341652014-03-23 22:32:09 -07001491 (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001492}
1493
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001494#else /* #ifdef CONFIG_RCU_BOOST */
1495
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001496static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001497{
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001498 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001499}
1500
Paul E. McKenneya46e0892011-06-15 15:47:09 -07001501static void invoke_rcu_callbacks_kthread(void)
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001502{
Paul E. McKenneya46e0892011-06-15 15:47:09 -07001503 WARN_ON_ONCE(1);
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001504}
1505
Paul E. McKenneydff16722011-11-29 15:57:13 -08001506static bool rcu_is_callbacks_kthread(void)
1507{
1508 return false;
1509}
1510
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001511static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1512{
1513}
1514
Thomas Gleixner5d01bbd2012-07-16 10:42:35 +00001515static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001516{
1517}
1518
Paul E. McKenneyb0d30412011-07-10 15:57:35 -07001519static int __init rcu_scheduler_really_started(void)
1520{
1521 rcu_scheduler_fully_active = 1;
1522 return 0;
1523}
1524early_initcall(rcu_scheduler_really_started);
1525
Paul Gortmaker49fb4c62013-06-19 14:52:21 -04001526static void rcu_prepare_kthreads(int cpu)
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001527{
1528}
1529
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001530#endif /* #else #ifdef CONFIG_RCU_BOOST */
1531
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001532#if !defined(CONFIG_RCU_FAST_NO_HZ)
1533
1534/*
1535 * Check to see if any future RCU-related work will need to be done
1536 * by the current CPU, even if none need be done immediately, returning
1537 * 1 if so. This function is part of the RCU implementation; it is -not-
1538 * an exported member of the RCU API.
1539 *
Paul E. McKenney7cb92492011-11-28 12:28:34 -08001540 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
1541 * any flavor of RCU.
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001542 */
Paul E. McKenneyffa83fb2013-11-17 19:27:16 -08001543#ifndef CONFIG_RCU_NOCB_CPU_ALL
Paul E. McKenneyaa9b16302012-05-10 16:41:44 -07001544int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001545{
Paul E. McKenneyaa9b16302012-05-10 16:41:44 -07001546 *delta_jiffies = ULONG_MAX;
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001547 return rcu_cpu_has_callbacks(cpu, NULL);
Paul E. McKenney7cb92492011-11-28 12:28:34 -08001548}
Paul E. McKenneyffa83fb2013-11-17 19:27:16 -08001549#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
Paul E. McKenney7cb92492011-11-28 12:28:34 -08001550
1551/*
1552 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
1553 * after it.
1554 */
1555static void rcu_cleanup_after_idle(int cpu)
1556{
1557}
1558
1559/*
Paul E. McKenneya858af22012-01-16 13:29:10 -08001560 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
Paul E. McKenneyaea1b352011-11-02 06:54:54 -07001561 * is nothing.
1562 */
1563static void rcu_prepare_for_idle(int cpu)
1564{
1565}
1566
Paul E. McKenneyc57afe82012-02-28 11:02:21 -08001567/*
1568 * Don't bother keeping a running count of the number of RCU callbacks
1569 * posted because CONFIG_RCU_FAST_NO_HZ=n.
1570 */
1571static void rcu_idle_count_callbacks_posted(void)
1572{
1573}
1574
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001575#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1576
Paul E. McKenneyf23f7fa2011-11-30 15:41:14 -08001577/*
1578 * This code is invoked when a CPU goes idle, at which point we want
1579 * to have the CPU do everything required for RCU so that it can enter
1580 * the energy-efficient dyntick-idle mode. This is handled by a
1581 * state machine implemented by rcu_prepare_for_idle() below.
1582 *
1583 * The following three proprocessor symbols control this state machine:
1584 *
Paul E. McKenneyf23f7fa2011-11-30 15:41:14 -08001585 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
1586 * to sleep in dyntick-idle mode with RCU callbacks pending. This
1587 * is sized to be roughly one RCU grace period. Those energy-efficiency
1588 * benchmarkers who might otherwise be tempted to set this to a large
1589 * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
1590 * system. And if you are -that- concerned about energy efficiency,
1591 * just power the system down and be done with it!
Paul E. McKenney778d2502012-01-10 14:13:24 -08001592 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
1593 * permitted to sleep in dyntick-idle mode with only lazy RCU
1594 * callbacks pending. Setting this too high can OOM your system.
Paul E. McKenneyf23f7fa2011-11-30 15:41:14 -08001595 *
1596 * The values below work well in practice. If future workloads require
1597 * adjustment, they can be converted into kernel config parameters, though
1598 * making the state machine smarter might be a better option.
1599 */
Paul E. McKenneye84c48a2012-06-04 20:45:10 -07001600#define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
Paul E. McKenney778d2502012-01-10 14:13:24 -08001601#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
Paul E. McKenneyf23f7fa2011-11-30 15:41:14 -08001602
Paul E. McKenney5e44ce32012-12-12 12:35:29 -08001603static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
1604module_param(rcu_idle_gp_delay, int, 0644);
1605static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
1606module_param(rcu_idle_lazy_gp_delay, int, 0644);
1607
Thomas Gleixnerd689fe22013-11-13 21:01:57 +01001608extern int tick_nohz_active;
Paul E. McKenney9d2ad242012-06-24 10:15:02 -07001609
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001610/*
Paul E. McKenneyc2298282013-08-25 21:20:47 -07001611 * Try to advance callbacks for all flavors of RCU on the current CPU, but
1612 * only if it has been awhile since the last time we did so. Afterwards,
1613 * if there are any callbacks ready for immediate invocation, return true.
Paul E. McKenney486e2592012-01-06 14:11:30 -08001614 */
Paul E. McKenneyf1f399d2013-11-17 21:08:07 -08001615static bool __maybe_unused rcu_try_advance_all_cbs(void)
Paul E. McKenney486e2592012-01-06 14:11:30 -08001616{
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001617 bool cbs_ready = false;
1618 struct rcu_data *rdp;
Paul E. McKenneyc2298282013-08-25 21:20:47 -07001619 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001620 struct rcu_node *rnp;
1621 struct rcu_state *rsp;
Paul E. McKenney486e2592012-01-06 14:11:30 -08001622
Paul E. McKenneyc2298282013-08-25 21:20:47 -07001623 /* Exit early if we advanced recently. */
1624 if (jiffies == rdtp->last_advance_all)
1625 return 0;
1626 rdtp->last_advance_all = jiffies;
1627
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001628 for_each_rcu_flavor(rsp) {
1629 rdp = this_cpu_ptr(rsp->rda);
1630 rnp = rdp->mynode;
Paul E. McKenney486e2592012-01-06 14:11:30 -08001631
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001632 /*
1633 * Don't bother checking unless a grace period has
1634 * completed since we last checked and there are
1635 * callbacks not yet ready to invoke.
1636 */
1637 if (rdp->completed != rnp->completed &&
1638 rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL])
Paul E. McKenney470716f2013-03-19 11:32:11 -07001639 note_gp_changes(rsp, rdp);
Paul E. McKenney486e2592012-01-06 14:11:30 -08001640
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001641 if (cpu_has_callbacks_ready_to_invoke(rdp))
1642 cbs_ready = true;
1643 }
1644 return cbs_ready;
Paul E. McKenney486e2592012-01-06 14:11:30 -08001645}
1646
1647/*
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001648 * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
1649 * to invoke. If the CPU has callbacks, try to advance them. Tell the
1650 * caller to set the timeout based on whether or not there are non-lazy
1651 * callbacks.
Paul E. McKenneyaa9b16302012-05-10 16:41:44 -07001652 *
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001653 * The caller must have disabled interrupts.
Paul E. McKenneyaa9b16302012-05-10 16:41:44 -07001654 */
Paul E. McKenneyffa83fb2013-11-17 19:27:16 -08001655#ifndef CONFIG_RCU_NOCB_CPU_ALL
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001656int rcu_needs_cpu(int cpu, unsigned long *dj)
Paul E. McKenneyaa9b16302012-05-10 16:41:44 -07001657{
1658 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1659
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001660 /* Snapshot to detect later posting of non-lazy callback. */
1661 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1662
Paul E. McKenneyaa9b16302012-05-10 16:41:44 -07001663 /* If no callbacks, RCU doesn't need the CPU. */
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001664 if (!rcu_cpu_has_callbacks(cpu, &rdtp->all_lazy)) {
1665 *dj = ULONG_MAX;
Paul E. McKenneyaa9b16302012-05-10 16:41:44 -07001666 return 0;
1667 }
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001668
1669 /* Attempt to advance callbacks. */
1670 if (rcu_try_advance_all_cbs()) {
1671 /* Some ready to invoke, so initiate later invocation. */
1672 invoke_rcu_core();
Paul E. McKenneyaa9b16302012-05-10 16:41:44 -07001673 return 1;
1674 }
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001675 rdtp->last_accelerate = jiffies;
1676
1677 /* Request timer delay depending on laziness, and round. */
Paul E. McKenney6faf7282013-05-13 06:53:37 -07001678 if (!rdtp->all_lazy) {
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001679 *dj = round_up(rcu_idle_gp_delay + jiffies,
1680 rcu_idle_gp_delay) - jiffies;
Paul E. McKenneye84c48a2012-06-04 20:45:10 -07001681 } else {
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001682 *dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
Paul E. McKenneye84c48a2012-06-04 20:45:10 -07001683 }
Paul E. McKenneyaa9b16302012-05-10 16:41:44 -07001684 return 0;
1685}
Paul E. McKenneyffa83fb2013-11-17 19:27:16 -08001686#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
Paul E. McKenneyaa9b16302012-05-10 16:41:44 -07001687
1688/*
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001689 * Prepare a CPU for idle from an RCU perspective. The first major task
1690 * is to sense whether nohz mode has been enabled or disabled via sysfs.
1691 * The second major task is to check to see if a non-lazy callback has
1692 * arrived at a CPU that previously had only lazy callbacks. The third
1693 * major task is to accelerate (that is, assign grace-period numbers to)
1694 * any recently arrived callbacks.
Paul E. McKenneyaea1b352011-11-02 06:54:54 -07001695 *
1696 * The caller must have disabled interrupts.
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001697 */
Paul E. McKenneyaea1b352011-11-02 06:54:54 -07001698static void rcu_prepare_for_idle(int cpu)
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001699{
Paul E. McKenneyf1f399d2013-11-17 21:08:07 -08001700#ifndef CONFIG_RCU_NOCB_CPU_ALL
Paul E. McKenney48a76392014-03-11 13:02:16 -07001701 bool needwake;
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001702 struct rcu_data *rdp;
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07001703 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001704 struct rcu_node *rnp;
1705 struct rcu_state *rsp;
Paul E. McKenney9d2ad242012-06-24 10:15:02 -07001706 int tne;
1707
1708 /* Handle nohz enablement switches conservatively. */
Thomas Gleixnerd689fe22013-11-13 21:01:57 +01001709 tne = ACCESS_ONCE(tick_nohz_active);
Paul E. McKenney9d2ad242012-06-24 10:15:02 -07001710 if (tne != rdtp->tick_nohz_enabled_snap) {
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001711 if (rcu_cpu_has_callbacks(cpu, NULL))
Paul E. McKenney9d2ad242012-06-24 10:15:02 -07001712 invoke_rcu_core(); /* force nohz to see update. */
1713 rdtp->tick_nohz_enabled_snap = tne;
1714 return;
1715 }
1716 if (!tne)
1717 return;
Paul E. McKenneyf511fc62012-03-15 12:16:26 -07001718
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001719 /* If this is a no-CBs CPU, no callbacks, just return. */
Linus Torvalds534c97b2013-05-05 13:23:27 -07001720 if (rcu_is_nocb_cpu(cpu))
Paul E. McKenney9a0c6fe2012-06-28 12:33:51 -07001721 return;
Paul E. McKenney9a0c6fe2012-06-28 12:33:51 -07001722
Paul E. McKenney3084f2f2011-11-22 17:07:11 -08001723 /*
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001724 * If a non-lazy callback arrived at a CPU having only lazy
1725 * callbacks, invoke RCU core for the side-effect of recalculating
1726 * idle duration on re-entry to idle.
Paul E. McKenneyc57afe82012-02-28 11:02:21 -08001727 */
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001728 if (rdtp->all_lazy &&
1729 rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
Paul E. McKenneyc337f8f2013-09-05 17:02:11 -07001730 rdtp->all_lazy = false;
1731 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
Paul E. McKenneya46e0892011-06-15 15:47:09 -07001732 invoke_rcu_core();
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001733 return;
1734 }
1735
1736 /*
1737 * If we have not yet accelerated this jiffy, accelerate all
1738 * callbacks on this CPU.
1739 */
1740 if (rdtp->last_accelerate == jiffies)
1741 return;
1742 rdtp->last_accelerate = jiffies;
1743 for_each_rcu_flavor(rsp) {
1744 rdp = per_cpu_ptr(rsp->rda, cpu);
1745 if (!*rdp->nxttail[RCU_DONE_TAIL])
1746 continue;
1747 rnp = rdp->mynode;
1748 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
Paul E. McKenney6303b9c2013-12-11 13:59:10 -08001749 smp_mb__after_unlock_lock();
Paul E. McKenney48a76392014-03-11 13:02:16 -07001750 needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001751 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
Paul E. McKenney48a76392014-03-11 13:02:16 -07001752 if (needwake)
1753 rcu_gp_kthread_wake(rsp);
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001754 }
Paul E. McKenneyf1f399d2013-11-17 21:08:07 -08001755#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001756}
1757
1758/*
1759 * Clean up for exit from idle. Attempt to advance callbacks based on
1760 * any grace periods that elapsed while the CPU was idle, and if any
1761 * callbacks are now ready to invoke, initiate invocation.
1762 */
1763static void rcu_cleanup_after_idle(int cpu)
1764{
Paul E. McKenneyf1f399d2013-11-17 21:08:07 -08001765#ifndef CONFIG_RCU_NOCB_CPU_ALL
Linus Torvalds534c97b2013-05-05 13:23:27 -07001766 if (rcu_is_nocb_cpu(cpu))
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001767 return;
Paul E. McKenney7a497c92013-08-22 18:16:16 -07001768 if (rcu_try_advance_all_cbs())
1769 invoke_rcu_core();
Paul E. McKenneyf1f399d2013-11-17 21:08:07 -08001770#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001771}
1772
Paul E. McKenneyc57afe82012-02-28 11:02:21 -08001773/*
Paul E. McKenney98248a02012-05-03 15:38:10 -07001774 * Keep a running count of the number of non-lazy callbacks posted
1775 * on this CPU. This running counter (which is never decremented) allows
1776 * rcu_prepare_for_idle() to detect when something out of the idle loop
1777 * posts a callback, even if an equal number of callbacks are invoked.
1778 * Of course, callbacks should only be posted from within a trace event
1779 * designed to be called from idle or from within RCU_NONIDLE().
Paul E. McKenneyc57afe82012-02-28 11:02:21 -08001780 */
1781static void rcu_idle_count_callbacks_posted(void)
1782{
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07001783 __this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
Paul E. McKenneyc57afe82012-02-28 11:02:21 -08001784}
1785
Paul E. McKenneyb626c1b2012-06-11 17:39:43 -07001786/*
1787 * Data for flushing lazy RCU callbacks at OOM time.
1788 */
1789static atomic_t oom_callback_count;
1790static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);
1791
1792/*
1793 * RCU OOM callback -- decrement the outstanding count and deliver the
1794 * wake-up if we are the last one.
1795 */
1796static void rcu_oom_callback(struct rcu_head *rhp)
1797{
1798 if (atomic_dec_and_test(&oom_callback_count))
1799 wake_up(&oom_callback_wq);
1800}
1801
1802/*
1803 * Post an rcu_oom_notify callback on the current CPU if it has at
1804 * least one lazy callback. This will unnecessarily post callbacks
1805 * to CPUs that already have a non-lazy callback at the end of their
1806 * callback list, but this is an infrequent operation, so accept some
1807 * extra overhead to keep things simple.
1808 */
1809static void rcu_oom_notify_cpu(void *unused)
1810{
1811 struct rcu_state *rsp;
1812 struct rcu_data *rdp;
1813
1814 for_each_rcu_flavor(rsp) {
Christoph Lameterfa07a582014-04-15 12:20:12 -07001815 rdp = raw_cpu_ptr(rsp->rda);
Paul E. McKenneyb626c1b2012-06-11 17:39:43 -07001816 if (rdp->qlen_lazy != 0) {
1817 atomic_inc(&oom_callback_count);
1818 rsp->call(&rdp->oom_head, rcu_oom_callback);
1819 }
1820 }
1821}
1822
1823/*
1824 * If low on memory, ensure that each CPU has a non-lazy callback.
1825 * This will wake up CPUs that have only lazy callbacks, in turn
1826 * ensuring that they free up the corresponding memory in a timely manner.
1827 * Because an uncertain amount of memory will be freed in some uncertain
1828 * timeframe, we do not claim to have freed anything.
1829 */
1830static int rcu_oom_notify(struct notifier_block *self,
1831 unsigned long notused, void *nfreed)
1832{
1833 int cpu;
1834
1835 /* Wait for callbacks from earlier instance to complete. */
1836 wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);
Paul E. McKenney78e4bc32013-09-24 15:04:06 -07001837 smp_mb(); /* Ensure callback reuse happens after callback invocation. */
Paul E. McKenneyb626c1b2012-06-11 17:39:43 -07001838
1839 /*
1840 * Prevent premature wakeup: ensure that all increments happen
1841 * before there is a chance of the counter reaching zero.
1842 */
1843 atomic_set(&oom_callback_count, 1);
1844
1845 get_online_cpus();
1846 for_each_online_cpu(cpu) {
1847 smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
1848 cond_resched();
1849 }
1850 put_online_cpus();
1851
1852 /* Unconditionally decrement: no need to wake ourselves up. */
1853 atomic_dec(&oom_callback_count);
1854
1855 return NOTIFY_OK;
1856}
1857
1858static struct notifier_block rcu_oom_nb = {
1859 .notifier_call = rcu_oom_notify
1860};
1861
1862static int __init rcu_register_oom_notifier(void)
1863{
1864 register_oom_notifier(&rcu_oom_nb);
1865 return 0;
1866}
1867early_initcall(rcu_register_oom_notifier);
1868
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001869#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
Paul E. McKenneya858af22012-01-16 13:29:10 -08001870
1871#ifdef CONFIG_RCU_CPU_STALL_INFO
1872
1873#ifdef CONFIG_RCU_FAST_NO_HZ
1874
1875static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
1876{
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07001877 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001878 unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
Paul E. McKenneya858af22012-01-16 13:29:10 -08001879
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -08001880 sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
1881 rdtp->last_accelerate & 0xffff, jiffies & 0xffff,
1882 ulong2long(nlpd),
1883 rdtp->all_lazy ? 'L' : '.',
1884 rdtp->tick_nohz_enabled_snap ? '.' : 'D');
Paul E. McKenneya858af22012-01-16 13:29:10 -08001885}
1886
1887#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
1888
1889static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
1890{
Carsten Emde1c17e4d2012-06-19 10:43:16 +02001891 *cp = '\0';
Paul E. McKenneya858af22012-01-16 13:29:10 -08001892}
1893
1894#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
1895
1896/* Initiate the stall-info list. */
1897static void print_cpu_stall_info_begin(void)
1898{
Paul E. McKenneyefc151c2013-03-18 16:24:11 -07001899 pr_cont("\n");
Paul E. McKenneya858af22012-01-16 13:29:10 -08001900}
1901
1902/*
1903 * Print out diagnostic information for the specified stalled CPU.
1904 *
1905 * If the specified CPU is aware of the current RCU grace period
1906 * (flavor specified by rsp), then print the number of scheduling
1907 * clock interrupts the CPU has taken during the time that it has
1908 * been aware. Otherwise, print the number of RCU grace periods
1909 * that this CPU is ignorant of, for example, "1" if the CPU was
1910 * aware of the previous grace period.
1911 *
1912 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
1913 */
1914static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
1915{
1916 char fast_no_hz[72];
1917 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1918 struct rcu_dynticks *rdtp = rdp->dynticks;
1919 char *ticks_title;
1920 unsigned long ticks_value;
1921
1922 if (rsp->gpnum == rdp->gpnum) {
1923 ticks_title = "ticks this GP";
1924 ticks_value = rdp->ticks_this_gp;
1925 } else {
1926 ticks_title = "GPs behind";
1927 ticks_value = rsp->gpnum - rdp->gpnum;
1928 }
1929 print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
Paul E. McKenneyefc151c2013-03-18 16:24:11 -07001930 pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n",
Paul E. McKenneya858af22012-01-16 13:29:10 -08001931 cpu, ticks_value, ticks_title,
1932 atomic_read(&rdtp->dynticks) & 0xfff,
1933 rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
Paul E. McKenney62310692013-03-06 13:37:09 -08001934 rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
Paul E. McKenneya858af22012-01-16 13:29:10 -08001935 fast_no_hz);
1936}
1937
1938/* Terminate the stall-info list. */
1939static void print_cpu_stall_info_end(void)
1940{
Paul E. McKenneyefc151c2013-03-18 16:24:11 -07001941 pr_err("\t");
Paul E. McKenneya858af22012-01-16 13:29:10 -08001942}
1943
1944/* Zero ->ticks_this_gp for all flavors of RCU. */
1945static void zero_cpu_stall_ticks(struct rcu_data *rdp)
1946{
1947 rdp->ticks_this_gp = 0;
Paul E. McKenney62310692013-03-06 13:37:09 -08001948 rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
Paul E. McKenneya858af22012-01-16 13:29:10 -08001949}
1950
1951/* Increment ->ticks_this_gp for all flavors of RCU. */
1952static void increment_cpu_stall_ticks(void)
1953{
Paul E. McKenney115f7a72012-08-10 13:55:03 -07001954 struct rcu_state *rsp;
1955
1956 for_each_rcu_flavor(rsp)
Christoph Lameterfa07a582014-04-15 12:20:12 -07001957 raw_cpu_inc(rsp->rda->ticks_this_gp);
Paul E. McKenneya858af22012-01-16 13:29:10 -08001958}
1959
1960#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
1961
1962static void print_cpu_stall_info_begin(void)
1963{
Paul E. McKenneyefc151c2013-03-18 16:24:11 -07001964 pr_cont(" {");
Paul E. McKenneya858af22012-01-16 13:29:10 -08001965}
1966
1967static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
1968{
Paul E. McKenneyefc151c2013-03-18 16:24:11 -07001969 pr_cont(" %d", cpu);
Paul E. McKenneya858af22012-01-16 13:29:10 -08001970}
1971
1972static void print_cpu_stall_info_end(void)
1973{
Paul E. McKenneyefc151c2013-03-18 16:24:11 -07001974 pr_cont("} ");
Paul E. McKenneya858af22012-01-16 13:29:10 -08001975}
1976
1977static void zero_cpu_stall_ticks(struct rcu_data *rdp)
1978{
1979}
1980
1981static void increment_cpu_stall_ticks(void)
1982{
1983}
1984
1985#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07001986
1987#ifdef CONFIG_RCU_NOCB_CPU
1988
1989/*
1990 * Offload callback processing from the boot-time-specified set of CPUs
1991 * specified by rcu_nocb_mask. For each CPU in the set, there is a
1992 * kthread created that pulls the callbacks from the corresponding CPU,
1993 * waits for a grace period to elapse, and invokes the callbacks.
1994 * The no-CBs CPUs do a wake_up() on their kthread when they insert
1995 * a callback into any empty list, unless the rcu_nocb_poll boot parameter
1996 * has been specified, in which case each kthread actively polls its
1997 * CPU. (Which isn't so great for energy efficiency, but which does
1998 * reduce RCU's overhead on that CPU.)
1999 *
2000 * This is intended to be used in conjunction with Frederic Weisbecker's
2001 * adaptive-idle work, which would seriously reduce OS jitter on CPUs
2002 * running CPU-bound user-mode computations.
2003 *
2004 * Offloading of callback processing could also in theory be used as
2005 * an energy-efficiency measure because CPUs with no RCU callbacks
2006 * queued are more aggressive about entering dyntick-idle mode.
2007 */
2008
2009
2010/* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
2011static int __init rcu_nocb_setup(char *str)
2012{
2013 alloc_bootmem_cpumask_var(&rcu_nocb_mask);
2014 have_rcu_nocb_mask = true;
2015 cpulist_parse(str, rcu_nocb_mask);
2016 return 1;
2017}
2018__setup("rcu_nocbs=", rcu_nocb_setup);
2019
Paul Gortmaker1b0048a2012-12-20 13:19:22 -08002020static int __init parse_rcu_nocb_poll(char *arg)
2021{
2022 rcu_nocb_poll = 1;
2023 return 0;
2024}
2025early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
2026
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002027/*
Paul E. McKenney0446be42012-12-30 15:21:01 -08002028 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
2029 * grace period.
Paul E. McKenneydae6e642013-02-10 20:48:58 -08002030 */
Paul E. McKenney0446be42012-12-30 15:21:01 -08002031static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
Paul E. McKenneydae6e642013-02-10 20:48:58 -08002032{
Paul E. McKenney0446be42012-12-30 15:21:01 -08002033 wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]);
Paul E. McKenneydae6e642013-02-10 20:48:58 -08002034}
2035
2036/*
Paul E. McKenney8b425aa82012-12-30 13:06:35 -08002037 * Set the root rcu_node structure's ->need_future_gp field
Paul E. McKenneydae6e642013-02-10 20:48:58 -08002038 * based on the sum of those of all rcu_node structures. This does
2039 * double-count the root rcu_node structure's requests, but this
2040 * is necessary to handle the possibility of a rcu_nocb_kthread()
2041 * having awakened during the time that the rcu_node structures
2042 * were being updated for the end of the previous grace period.
2043 */
2044static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
2045{
Paul E. McKenney8b425aa82012-12-30 13:06:35 -08002046 rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;
Paul E. McKenneydae6e642013-02-10 20:48:58 -08002047}
2048
2049static void rcu_init_one_nocb(struct rcu_node *rnp)
2050{
2051 init_waitqueue_head(&rnp->nocb_gp_wq[0]);
2052 init_waitqueue_head(&rnp->nocb_gp_wq[1]);
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002053}
2054
Paul E. McKenney2f33b512013-11-17 18:25:48 -08002055#ifndef CONFIG_RCU_NOCB_CPU_ALL
Liu Ping Fan24342c92014-02-24 06:18:09 -08002056/* Is the specified CPU a no-CBs CPU? */
Frederic Weisbeckerd1e43fa2013-03-26 23:47:24 +01002057bool rcu_is_nocb_cpu(int cpu)
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002058{
2059 if (have_rcu_nocb_mask)
2060 return cpumask_test_cpu(cpu, rcu_nocb_mask);
2061 return false;
2062}
Paul E. McKenney2f33b512013-11-17 18:25:48 -08002063#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002064
2065/*
2066 * Enqueue the specified string of rcu_head structures onto the specified
2067 * CPU's no-CBs lists. The CPU is specified by rdp, the head of the
2068 * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy
2069 * counts are supplied by rhcount and rhcount_lazy.
2070 *
2071 * If warranted, also wake up the kthread servicing this CPUs queues.
2072 */
2073static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
2074 struct rcu_head *rhp,
2075 struct rcu_head **rhtp,
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07002076 int rhcount, int rhcount_lazy,
2077 unsigned long flags)
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002078{
2079 int len;
2080 struct rcu_head **old_rhpp;
2081 struct task_struct *t;
2082
2083 /* Enqueue the callback on the nocb list and update counts. */
2084 old_rhpp = xchg(&rdp->nocb_tail, rhtp);
2085 ACCESS_ONCE(*old_rhpp) = rhp;
2086 atomic_long_add(rhcount, &rdp->nocb_q_count);
2087 atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
2088
2089 /* If we are not being polled and there is a kthread, awaken it ... */
2090 t = ACCESS_ONCE(rdp->nocb_kthread);
Paul E. McKenney25e03a72013-10-15 12:47:04 -07002091 if (rcu_nocb_poll || !t) {
Paul E. McKenney9261dd02013-08-14 16:24:26 -07002092 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2093 TPS("WakeNotPoll"));
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002094 return;
Paul E. McKenney9261dd02013-08-14 16:24:26 -07002095 }
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002096 len = atomic_long_read(&rdp->nocb_q_count);
2097 if (old_rhpp == &rdp->nocb_head) {
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07002098 if (!irqs_disabled_flags(flags)) {
2099 wake_up(&rdp->nocb_wq); /* ... if queue was empty ... */
2100 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2101 TPS("WakeEmpty"));
2102 } else {
2103 rdp->nocb_defer_wakeup = true;
2104 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2105 TPS("WakeEmptyIsDeferred"));
2106 }
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002107 rdp->qlen_last_fqs_check = 0;
2108 } else if (len > rdp->qlen_last_fqs_check + qhimark) {
2109 wake_up_process(t); /* ... or if many callbacks queued. */
2110 rdp->qlen_last_fqs_check = LONG_MAX / 2;
Paul E. McKenney9261dd02013-08-14 16:24:26 -07002111 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeOvf"));
2112 } else {
2113 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002114 }
2115 return;
2116}
2117
2118/*
2119 * This is a helper for __call_rcu(), which invokes this when the normal
2120 * callback queue is inoperable. If this is not a no-CBs CPU, this
2121 * function returns failure back to __call_rcu(), which can complain
2122 * appropriately.
2123 *
2124 * Otherwise, this function queues the callback where the corresponding
2125 * "rcuo" kthread can find it.
2126 */
2127static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07002128 bool lazy, unsigned long flags)
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002129{
2130
Frederic Weisbeckerd1e43fa2013-03-26 23:47:24 +01002131 if (!rcu_is_nocb_cpu(rdp->cpu))
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002132 return 0;
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07002133 __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags);
Paul E. McKenney21e7a602013-02-09 17:42:16 -08002134 if (__is_kfree_rcu_offset((unsigned long)rhp->func))
2135 trace_rcu_kfree_callback(rdp->rsp->name, rhp,
2136 (unsigned long)rhp->func,
Paul E. McKenney756cbf62013-08-15 10:12:12 -07002137 -atomic_long_read(&rdp->nocb_q_count_lazy),
2138 -atomic_long_read(&rdp->nocb_q_count));
Paul E. McKenney21e7a602013-02-09 17:42:16 -08002139 else
2140 trace_rcu_callback(rdp->rsp->name, rhp,
Paul E. McKenney756cbf62013-08-15 10:12:12 -07002141 -atomic_long_read(&rdp->nocb_q_count_lazy),
2142 -atomic_long_read(&rdp->nocb_q_count));
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002143 return 1;
2144}
2145
2146/*
2147 * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
2148 * not a no-CBs CPU.
2149 */
2150static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07002151 struct rcu_data *rdp,
2152 unsigned long flags)
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002153{
2154 long ql = rsp->qlen;
2155 long qll = rsp->qlen_lazy;
2156
2157 /* If this is not a no-CBs CPU, tell the caller to do it the old way. */
Frederic Weisbeckerd1e43fa2013-03-26 23:47:24 +01002158 if (!rcu_is_nocb_cpu(smp_processor_id()))
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002159 return 0;
2160 rsp->qlen = 0;
2161 rsp->qlen_lazy = 0;
2162
2163 /* First, enqueue the donelist, if any. This preserves CB ordering. */
2164 if (rsp->orphan_donelist != NULL) {
2165 __call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist,
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07002166 rsp->orphan_donetail, ql, qll, flags);
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002167 ql = qll = 0;
2168 rsp->orphan_donelist = NULL;
2169 rsp->orphan_donetail = &rsp->orphan_donelist;
2170 }
2171 if (rsp->orphan_nxtlist != NULL) {
2172 __call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist,
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07002173 rsp->orphan_nxttail, ql, qll, flags);
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002174 ql = qll = 0;
2175 rsp->orphan_nxtlist = NULL;
2176 rsp->orphan_nxttail = &rsp->orphan_nxtlist;
2177 }
2178 return 1;
2179}
2180
2181/*
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002182 * If necessary, kick off a new grace period, and either way wait
2183 * for a subsequent grace period to complete.
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002184 */
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002185static void rcu_nocb_wait_gp(struct rcu_data *rdp)
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002186{
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002187 unsigned long c;
Paul E. McKenneydae6e642013-02-10 20:48:58 -08002188 bool d;
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002189 unsigned long flags;
Paul E. McKenney48a76392014-03-11 13:02:16 -07002190 bool needwake;
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002191 struct rcu_node *rnp = rdp->mynode;
2192
2193 raw_spin_lock_irqsave(&rnp->lock, flags);
Paul E. McKenney6303b9c2013-12-11 13:59:10 -08002194 smp_mb__after_unlock_lock();
Paul E. McKenney48a76392014-03-11 13:02:16 -07002195 needwake = rcu_start_future_gp(rnp, rdp, &c);
Paul E. McKenney0446be42012-12-30 15:21:01 -08002196 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenney48a76392014-03-11 13:02:16 -07002197 if (needwake)
2198 rcu_gp_kthread_wake(rdp->rsp);
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002199
2200 /*
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002201 * Wait for the grace period. Do so interruptibly to avoid messing
2202 * up the load average.
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002203 */
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04002204 trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait"));
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002205 for (;;) {
Paul E. McKenneydae6e642013-02-10 20:48:58 -08002206 wait_event_interruptible(
2207 rnp->nocb_gp_wq[c & 0x1],
2208 (d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c)));
2209 if (likely(d))
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002210 break;
Paul E. McKenneydae6e642013-02-10 20:48:58 -08002211 flush_signals(current);
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04002212 trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait"));
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002213 }
Steven Rostedt (Red Hat)f7f7bac2013-07-12 17:18:47 -04002214 trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait"));
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002215 smp_mb(); /* Ensure that CB invocation happens after GP end. */
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002216}
2217
2218/*
2219 * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
2220 * callbacks queued by the corresponding no-CBs CPU.
2221 */
2222static int rcu_nocb_kthread(void *arg)
2223{
2224 int c, cl;
Paul E. McKenney69a79bb2013-08-15 13:23:23 -07002225 bool firsttime = 1;
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002226 struct rcu_head *list;
2227 struct rcu_head *next;
2228 struct rcu_head **tail;
2229 struct rcu_data *rdp = arg;
2230
2231 /* Each pass through this loop invokes one batch of callbacks */
2232 for (;;) {
2233 /* If not polling, wait for next batch of callbacks. */
Paul E. McKenney69a79bb2013-08-15 13:23:23 -07002234 if (!rcu_nocb_poll) {
2235 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2236 TPS("Sleep"));
Paul Gortmaker353af9c2012-12-20 09:35:02 -08002237 wait_event_interruptible(rdp->nocb_wq, rdp->nocb_head);
Paul E. McKenney78e4bc32013-09-24 15:04:06 -07002238 /* Memory barrier provide by xchg() below. */
Paul E. McKenney69a79bb2013-08-15 13:23:23 -07002239 } else if (firsttime) {
2240 firsttime = 0;
2241 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2242 TPS("Poll"));
2243 }
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002244 list = ACCESS_ONCE(rdp->nocb_head);
2245 if (!list) {
Paul E. McKenney9261dd02013-08-14 16:24:26 -07002246 if (!rcu_nocb_poll)
2247 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2248 TPS("WokeEmpty"));
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002249 schedule_timeout_interruptible(1);
Paul Gortmaker353af9c2012-12-20 09:35:02 -08002250 flush_signals(current);
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002251 continue;
2252 }
Paul E. McKenney69a79bb2013-08-15 13:23:23 -07002253 firsttime = 1;
Paul E. McKenney9261dd02013-08-14 16:24:26 -07002254 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2255 TPS("WokeNonEmpty"));
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002256
2257 /*
2258 * Extract queued callbacks, update counts, and wait
2259 * for a grace period to elapse.
2260 */
2261 ACCESS_ONCE(rdp->nocb_head) = NULL;
2262 tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
2263 c = atomic_long_xchg(&rdp->nocb_q_count, 0);
2264 cl = atomic_long_xchg(&rdp->nocb_q_count_lazy, 0);
2265 ACCESS_ONCE(rdp->nocb_p_count) += c;
2266 ACCESS_ONCE(rdp->nocb_p_count_lazy) += cl;
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002267 rcu_nocb_wait_gp(rdp);
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002268
2269 /* Each pass through the following loop invokes a callback. */
2270 trace_rcu_batch_start(rdp->rsp->name, cl, c, -1);
2271 c = cl = 0;
2272 while (list) {
2273 next = list->next;
2274 /* Wait for enqueuing to complete, if needed. */
2275 while (next == NULL && &list->next != tail) {
Paul E. McKenney69a79bb2013-08-15 13:23:23 -07002276 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2277 TPS("WaitQueue"));
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002278 schedule_timeout_interruptible(1);
Paul E. McKenney69a79bb2013-08-15 13:23:23 -07002279 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2280 TPS("WokeQueue"));
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002281 next = list->next;
2282 }
2283 debug_rcu_head_unqueue(list);
2284 local_bh_disable();
2285 if (__rcu_reclaim(rdp->rsp->name, list))
2286 cl++;
2287 c++;
2288 local_bh_enable();
2289 list = next;
2290 }
2291 trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
2292 ACCESS_ONCE(rdp->nocb_p_count) -= c;
2293 ACCESS_ONCE(rdp->nocb_p_count_lazy) -= cl;
Paul E. McKenneyc635a4e12012-10-29 07:29:20 -07002294 rdp->n_nocbs_invoked += c;
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002295 }
2296 return 0;
2297}
2298
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07002299/* Is a deferred wakeup of rcu_nocb_kthread() required? */
2300static bool rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2301{
2302 return ACCESS_ONCE(rdp->nocb_defer_wakeup);
2303}
2304
2305/* Do a deferred wakeup of rcu_nocb_kthread(). */
2306static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2307{
2308 if (!rcu_nocb_need_deferred_wakeup(rdp))
2309 return;
2310 ACCESS_ONCE(rdp->nocb_defer_wakeup) = false;
2311 wake_up(&rdp->nocb_wq);
2312 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWakeEmpty"));
2313}
2314
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002315/* Initialize per-rcu_data variables for no-CBs CPUs. */
2316static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2317{
2318 rdp->nocb_tail = &rdp->nocb_head;
2319 init_waitqueue_head(&rdp->nocb_wq);
2320}
2321
2322/* Create a kthread for each RCU flavor for each no-CBs CPU. */
2323static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
2324{
2325 int cpu;
2326 struct rcu_data *rdp;
2327 struct task_struct *t;
2328
2329 if (rcu_nocb_mask == NULL)
2330 return;
2331 for_each_cpu(cpu, rcu_nocb_mask) {
2332 rdp = per_cpu_ptr(rsp->rda, cpu);
Paul E. McKenneya4889852012-12-03 08:16:28 -08002333 t = kthread_run(rcu_nocb_kthread, rdp,
2334 "rcuo%c/%d", rsp->abbr, cpu);
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002335 BUG_ON(IS_ERR(t));
2336 ACCESS_ONCE(rdp->nocb_kthread) = t;
2337 }
2338}
2339
2340/* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002341static bool init_nocb_callback_list(struct rcu_data *rdp)
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002342{
2343 if (rcu_nocb_mask == NULL ||
2344 !cpumask_test_cpu(rdp->cpu, rcu_nocb_mask))
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002345 return false;
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002346 rdp->nxttail[RCU_NEXT_TAIL] = NULL;
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002347 return true;
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002348}
2349
2350#else /* #ifdef CONFIG_RCU_NOCB_CPU */
2351
Paul E. McKenney0446be42012-12-30 15:21:01 -08002352static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
Paul E. McKenneydae6e642013-02-10 20:48:58 -08002353{
Paul E. McKenneydae6e642013-02-10 20:48:58 -08002354}
2355
2356static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
2357{
2358}
2359
2360static void rcu_init_one_nocb(struct rcu_node *rnp)
2361{
2362}
2363
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002364static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07002365 bool lazy, unsigned long flags)
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002366{
2367 return 0;
2368}
2369
2370static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07002371 struct rcu_data *rdp,
2372 unsigned long flags)
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002373{
2374 return 0;
2375}
2376
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002377static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2378{
2379}
2380
Paul E. McKenney96d3fd02013-10-04 14:33:34 -07002381static bool rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2382{
2383 return false;
2384}
2385
2386static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2387{
2388}
2389
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002390static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
2391{
2392}
2393
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002394static bool init_nocb_callback_list(struct rcu_data *rdp)
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002395{
Paul E. McKenney34ed62462013-01-07 13:37:42 -08002396 return false;
Paul E. McKenney3fbfbf72012-08-19 21:35:53 -07002397}
2398
2399#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
Paul E. McKenney65d798f2013-04-12 16:19:10 -07002400
2401/*
2402 * An adaptive-ticks CPU can potentially execute in kernel mode for an
2403 * arbitrarily long period of time with the scheduling-clock tick turned
2404 * off. RCU will be paying attention to this CPU because it is in the
2405 * kernel, but the CPU cannot be guaranteed to be executing the RCU state
2406 * machine because the scheduling-clock tick has been disabled. Therefore,
2407 * if an adaptive-ticks CPU is failing to respond to the current grace
2408 * period and has not be idle from an RCU perspective, kick it.
2409 */
Paul E. McKenney4a81e832014-06-20 16:49:01 -07002410static void __maybe_unused rcu_kick_nohz_cpu(int cpu)
Paul E. McKenney65d798f2013-04-12 16:19:10 -07002411{
2412#ifdef CONFIG_NO_HZ_FULL
2413 if (tick_nohz_full_cpu(cpu))
2414 smp_send_reschedule(cpu);
2415#endif /* #ifdef CONFIG_NO_HZ_FULL */
2416}
Paul E. McKenney23332102013-06-21 12:34:33 -07002417
2418
2419#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
2420
2421/*
Paul E. McKenneyd4bd54f2013-06-21 14:51:40 -07002422 * Define RCU flavor that holds sysidle state. This needs to be the
2423 * most active flavor of RCU.
2424 */
2425#ifdef CONFIG_PREEMPT_RCU
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07002426static struct rcu_state *rcu_sysidle_state = &rcu_preempt_state;
Paul E. McKenneyd4bd54f2013-06-21 14:51:40 -07002427#else /* #ifdef CONFIG_PREEMPT_RCU */
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07002428static struct rcu_state *rcu_sysidle_state = &rcu_sched_state;
Paul E. McKenneyd4bd54f2013-06-21 14:51:40 -07002429#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
2430
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07002431static int full_sysidle_state; /* Current system-idle state. */
Paul E. McKenneyd4bd54f2013-06-21 14:51:40 -07002432#define RCU_SYSIDLE_NOT 0 /* Some CPU is not idle. */
2433#define RCU_SYSIDLE_SHORT 1 /* All CPUs idle for brief period. */
2434#define RCU_SYSIDLE_LONG 2 /* All CPUs idle for long enough. */
2435#define RCU_SYSIDLE_FULL 3 /* All CPUs idle, ready for sysidle. */
2436#define RCU_SYSIDLE_FULL_NOTED 4 /* Actually entered sysidle state. */
2437
2438/*
Paul E. McKenneyeb348b82013-06-21 13:00:57 -07002439 * Invoked to note exit from irq or task transition to idle. Note that
2440 * usermode execution does -not- count as idle here! After all, we want
2441 * to detect full-system idle states, not RCU quiescent states and grace
2442 * periods. The caller must have disabled interrupts.
2443 */
2444static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
2445{
2446 unsigned long j;
2447
2448 /* Adjust nesting, check for fully idle. */
2449 if (irq) {
2450 rdtp->dynticks_idle_nesting--;
2451 WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
2452 if (rdtp->dynticks_idle_nesting != 0)
2453 return; /* Still not fully idle. */
2454 } else {
2455 if ((rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) ==
2456 DYNTICK_TASK_NEST_VALUE) {
2457 rdtp->dynticks_idle_nesting = 0;
2458 } else {
2459 rdtp->dynticks_idle_nesting -= DYNTICK_TASK_NEST_VALUE;
2460 WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
2461 return; /* Still not fully idle. */
2462 }
2463 }
2464
2465 /* Record start of fully idle period. */
2466 j = jiffies;
2467 ACCESS_ONCE(rdtp->dynticks_idle_jiffies) = j;
Peter Zijlstra4e857c52014-03-17 18:06:10 +01002468 smp_mb__before_atomic();
Paul E. McKenneyeb348b82013-06-21 13:00:57 -07002469 atomic_inc(&rdtp->dynticks_idle);
Peter Zijlstra4e857c52014-03-17 18:06:10 +01002470 smp_mb__after_atomic();
Paul E. McKenneyeb348b82013-06-21 13:00:57 -07002471 WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1);
2472}
2473
2474/*
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07002475 * Unconditionally force exit from full system-idle state. This is
2476 * invoked when a normal CPU exits idle, but must be called separately
2477 * for the timekeeping CPU (tick_do_timer_cpu). The reason for this
2478 * is that the timekeeping CPU is permitted to take scheduling-clock
2479 * interrupts while the system is in system-idle state, and of course
2480 * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock
2481 * interrupt from any other type of interrupt.
2482 */
2483void rcu_sysidle_force_exit(void)
2484{
2485 int oldstate = ACCESS_ONCE(full_sysidle_state);
2486 int newoldstate;
2487
2488 /*
2489 * Each pass through the following loop attempts to exit full
2490 * system-idle state. If contention proves to be a problem,
2491 * a trylock-based contention tree could be used here.
2492 */
2493 while (oldstate > RCU_SYSIDLE_SHORT) {
2494 newoldstate = cmpxchg(&full_sysidle_state,
2495 oldstate, RCU_SYSIDLE_NOT);
2496 if (oldstate == newoldstate &&
2497 oldstate == RCU_SYSIDLE_FULL_NOTED) {
2498 rcu_kick_nohz_cpu(tick_do_timer_cpu);
2499 return; /* We cleared it, done! */
2500 }
2501 oldstate = newoldstate;
2502 }
2503 smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */
2504}
2505
2506/*
Paul E. McKenneyeb348b82013-06-21 13:00:57 -07002507 * Invoked to note entry to irq or task transition from idle. Note that
2508 * usermode execution does -not- count as idle here! The caller must
2509 * have disabled interrupts.
2510 */
2511static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
2512{
2513 /* Adjust nesting, check for already non-idle. */
2514 if (irq) {
2515 rdtp->dynticks_idle_nesting++;
2516 WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
2517 if (rdtp->dynticks_idle_nesting != 1)
2518 return; /* Already non-idle. */
2519 } else {
2520 /*
2521 * Allow for irq misnesting. Yes, it really is possible
2522 * to enter an irq handler then never leave it, and maybe
2523 * also vice versa. Handle both possibilities.
2524 */
2525 if (rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) {
2526 rdtp->dynticks_idle_nesting += DYNTICK_TASK_NEST_VALUE;
2527 WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
2528 return; /* Already non-idle. */
2529 } else {
2530 rdtp->dynticks_idle_nesting = DYNTICK_TASK_EXIT_IDLE;
2531 }
2532 }
2533
2534 /* Record end of idle period. */
Peter Zijlstra4e857c52014-03-17 18:06:10 +01002535 smp_mb__before_atomic();
Paul E. McKenneyeb348b82013-06-21 13:00:57 -07002536 atomic_inc(&rdtp->dynticks_idle);
Peter Zijlstra4e857c52014-03-17 18:06:10 +01002537 smp_mb__after_atomic();
Paul E. McKenneyeb348b82013-06-21 13:00:57 -07002538 WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1));
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07002539
2540 /*
2541 * If we are the timekeeping CPU, we are permitted to be non-idle
2542 * during a system-idle state. This must be the case, because
2543 * the timekeeping CPU has to take scheduling-clock interrupts
2544 * during the time that the system is transitioning to full
2545 * system-idle state. This means that the timekeeping CPU must
2546 * invoke rcu_sysidle_force_exit() directly if it does anything
2547 * more than take a scheduling-clock interrupt.
2548 */
2549 if (smp_processor_id() == tick_do_timer_cpu)
2550 return;
2551
2552 /* Update system-idle state: We are clearly no longer fully idle! */
2553 rcu_sysidle_force_exit();
2554}
2555
2556/*
2557 * Check to see if the current CPU is idle. Note that usermode execution
2558 * does not count as idle. The caller must have disabled interrupts.
2559 */
2560static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
2561 unsigned long *maxj)
2562{
2563 int cur;
2564 unsigned long j;
2565 struct rcu_dynticks *rdtp = rdp->dynticks;
2566
2567 /*
2568 * If some other CPU has already reported non-idle, if this is
2569 * not the flavor of RCU that tracks sysidle state, or if this
2570 * is an offline or the timekeeping CPU, nothing to do.
2571 */
2572 if (!*isidle || rdp->rsp != rcu_sysidle_state ||
2573 cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
2574 return;
Paul E. McKenneyeb757672013-06-21 17:10:40 -07002575 if (rcu_gp_in_progress(rdp->rsp))
2576 WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu);
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07002577
2578 /* Pick up current idle and NMI-nesting counter and check. */
2579 cur = atomic_read(&rdtp->dynticks_idle);
2580 if (cur & 0x1) {
2581 *isidle = false; /* We are not idle! */
2582 return;
2583 }
2584 smp_mb(); /* Read counters before timestamps. */
2585
2586 /* Pick up timestamps. */
2587 j = ACCESS_ONCE(rdtp->dynticks_idle_jiffies);
2588 /* If this CPU entered idle more recently, update maxj timestamp. */
2589 if (ULONG_CMP_LT(*maxj, j))
2590 *maxj = j;
2591}
2592
2593/*
2594 * Is this the flavor of RCU that is handling full-system idle?
2595 */
2596static bool is_sysidle_rcu_state(struct rcu_state *rsp)
2597{
2598 return rsp == rcu_sysidle_state;
2599}
2600
2601/*
2602 * Return a delay in jiffies based on the number of CPUs, rcu_node
2603 * leaf fanout, and jiffies tick rate. The idea is to allow larger
2604 * systems more time to transition to full-idle state in order to
2605 * avoid the cache thrashing that otherwise occur on the state variable.
2606 * Really small systems (less than a couple of tens of CPUs) should
2607 * instead use a single global atomically incremented counter, and later
2608 * versions of this will automatically reconfigure themselves accordingly.
2609 */
2610static unsigned long rcu_sysidle_delay(void)
2611{
2612 if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
2613 return 0;
2614 return DIV_ROUND_UP(nr_cpu_ids * HZ, rcu_fanout_leaf * 1000);
2615}
2616
2617/*
2618 * Advance the full-system-idle state. This is invoked when all of
2619 * the non-timekeeping CPUs are idle.
2620 */
2621static void rcu_sysidle(unsigned long j)
2622{
2623 /* Check the current state. */
2624 switch (ACCESS_ONCE(full_sysidle_state)) {
2625 case RCU_SYSIDLE_NOT:
2626
2627 /* First time all are idle, so note a short idle period. */
2628 ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_SHORT;
2629 break;
2630
2631 case RCU_SYSIDLE_SHORT:
2632
2633 /*
2634 * Idle for a bit, time to advance to next state?
2635 * cmpxchg failure means race with non-idle, let them win.
2636 */
2637 if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
2638 (void)cmpxchg(&full_sysidle_state,
2639 RCU_SYSIDLE_SHORT, RCU_SYSIDLE_LONG);
2640 break;
2641
2642 case RCU_SYSIDLE_LONG:
2643
2644 /*
2645 * Do an additional check pass before advancing to full.
2646 * cmpxchg failure means race with non-idle, let them win.
2647 */
2648 if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
2649 (void)cmpxchg(&full_sysidle_state,
2650 RCU_SYSIDLE_LONG, RCU_SYSIDLE_FULL);
2651 break;
2652
2653 default:
2654 break;
2655 }
2656}
2657
2658/*
2659 * Found a non-idle non-timekeeping CPU, so kick the system-idle state
2660 * back to the beginning.
2661 */
2662static void rcu_sysidle_cancel(void)
2663{
2664 smp_mb();
Paul E. McKenneybecb41b2014-04-07 13:34:07 -07002665 if (full_sysidle_state > RCU_SYSIDLE_SHORT)
2666 ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_NOT;
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07002667}
2668
2669/*
2670 * Update the sysidle state based on the results of a force-quiescent-state
2671 * scan of the CPUs' dyntick-idle state.
2672 */
2673static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
2674 unsigned long maxj, bool gpkt)
2675{
2676 if (rsp != rcu_sysidle_state)
2677 return; /* Wrong flavor, ignore. */
2678 if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
2679 return; /* Running state machine from timekeeping CPU. */
2680 if (isidle)
2681 rcu_sysidle(maxj); /* More idle! */
2682 else
2683 rcu_sysidle_cancel(); /* Idle is over. */
2684}
2685
2686/*
2687 * Wrapper for rcu_sysidle_report() when called from the grace-period
2688 * kthread's context.
2689 */
2690static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
2691 unsigned long maxj)
2692{
2693 rcu_sysidle_report(rsp, isidle, maxj, true);
2694}
2695
2696/* Callback and function for forcing an RCU grace period. */
2697struct rcu_sysidle_head {
2698 struct rcu_head rh;
2699 int inuse;
2700};
2701
2702static void rcu_sysidle_cb(struct rcu_head *rhp)
2703{
2704 struct rcu_sysidle_head *rshp;
2705
2706 /*
2707 * The following memory barrier is needed to replace the
2708 * memory barriers that would normally be in the memory
2709 * allocator.
2710 */
2711 smp_mb(); /* grace period precedes setting inuse. */
2712
2713 rshp = container_of(rhp, struct rcu_sysidle_head, rh);
2714 ACCESS_ONCE(rshp->inuse) = 0;
2715}
2716
2717/*
2718 * Check to see if the system is fully idle, other than the timekeeping CPU.
2719 * The caller must have disabled interrupts.
2720 */
2721bool rcu_sys_is_idle(void)
2722{
2723 static struct rcu_sysidle_head rsh;
2724 int rss = ACCESS_ONCE(full_sysidle_state);
2725
2726 if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu))
2727 return false;
2728
2729 /* Handle small-system case by doing a full scan of CPUs. */
2730 if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) {
2731 int oldrss = rss - 1;
2732
2733 /*
2734 * One pass to advance to each state up to _FULL.
2735 * Give up if any pass fails to advance the state.
2736 */
2737 while (rss < RCU_SYSIDLE_FULL && oldrss < rss) {
2738 int cpu;
2739 bool isidle = true;
2740 unsigned long maxj = jiffies - ULONG_MAX / 4;
2741 struct rcu_data *rdp;
2742
2743 /* Scan all the CPUs looking for nonidle CPUs. */
2744 for_each_possible_cpu(cpu) {
2745 rdp = per_cpu_ptr(rcu_sysidle_state->rda, cpu);
2746 rcu_sysidle_check_cpu(rdp, &isidle, &maxj);
2747 if (!isidle)
2748 break;
2749 }
2750 rcu_sysidle_report(rcu_sysidle_state,
2751 isidle, maxj, false);
2752 oldrss = rss;
2753 rss = ACCESS_ONCE(full_sysidle_state);
2754 }
2755 }
2756
2757 /* If this is the first observation of an idle period, record it. */
2758 if (rss == RCU_SYSIDLE_FULL) {
2759 rss = cmpxchg(&full_sysidle_state,
2760 RCU_SYSIDLE_FULL, RCU_SYSIDLE_FULL_NOTED);
2761 return rss == RCU_SYSIDLE_FULL;
2762 }
2763
2764 smp_mb(); /* ensure rss load happens before later caller actions. */
2765
2766 /* If already fully idle, tell the caller (in case of races). */
2767 if (rss == RCU_SYSIDLE_FULL_NOTED)
2768 return true;
2769
2770 /*
2771 * If we aren't there yet, and a grace period is not in flight,
2772 * initiate a grace period. Either way, tell the caller that
2773 * we are not there yet. We use an xchg() rather than an assignment
2774 * to make up for the memory barriers that would otherwise be
2775 * provided by the memory allocator.
2776 */
2777 if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL &&
2778 !rcu_gp_in_progress(rcu_sysidle_state) &&
2779 !rsh.inuse && xchg(&rsh.inuse, 1) == 0)
2780 call_rcu(&rsh.rh, rcu_sysidle_cb);
2781 return false;
Paul E. McKenneyeb348b82013-06-21 13:00:57 -07002782}
2783
2784/*
Paul E. McKenney23332102013-06-21 12:34:33 -07002785 * Initialize dynticks sysidle state for CPUs coming online.
2786 */
2787static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
2788{
2789 rdtp->dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE;
2790}
2791
2792#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
2793
Paul E. McKenneyeb348b82013-06-21 13:00:57 -07002794static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
2795{
2796}
2797
2798static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
2799{
2800}
2801
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07002802static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
2803 unsigned long *maxj)
2804{
2805}
2806
2807static bool is_sysidle_rcu_state(struct rcu_state *rsp)
2808{
2809 return false;
2810}
2811
2812static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
2813 unsigned long maxj)
2814{
2815}
2816
Paul E. McKenney23332102013-06-21 12:34:33 -07002817static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
2818{
2819}
2820
2821#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
Paul E. McKenneya0969322013-11-08 09:03:10 -08002822
2823/*
2824 * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
2825 * grace-period kthread will do force_quiescent_state() processing?
2826 * The idea is to avoid waking up RCU core processing on such a
2827 * CPU unless the grace period has extended for too long.
2828 *
2829 * This code relies on the fact that all NO_HZ_FULL CPUs are also
Paul Bolle52e2bb92014-02-09 14:35:11 +01002830 * CONFIG_RCU_NOCB_CPU CPUs.
Paul E. McKenneya0969322013-11-08 09:03:10 -08002831 */
2832static bool rcu_nohz_full_cpu(struct rcu_state *rsp)
2833{
2834#ifdef CONFIG_NO_HZ_FULL
2835 if (tick_nohz_full_cpu(smp_processor_id()) &&
2836 (!rcu_gp_in_progress(rsp) ||
2837 ULONG_CMP_LT(jiffies, ACCESS_ONCE(rsp->gp_start) + HZ)))
2838 return 1;
2839#endif /* #ifdef CONFIG_NO_HZ_FULL */
2840 return 0;
2841}
Paul E. McKenney5057f55e52014-04-01 11:20:36 -07002842
2843/*
2844 * Bind the grace-period kthread for the sysidle flavor of RCU to the
2845 * timekeeping CPU.
2846 */
2847static void rcu_bind_gp_kthread(void)
2848{
Paul E. McKenneyc0f489d2014-06-04 13:46:03 -07002849 int __maybe_unused cpu;
Paul E. McKenney5057f55e52014-04-01 11:20:36 -07002850
Paul E. McKenneyc0f489d2014-06-04 13:46:03 -07002851 if (!tick_nohz_full_enabled())
Paul E. McKenney5057f55e52014-04-01 11:20:36 -07002852 return;
Paul E. McKenneyc0f489d2014-06-04 13:46:03 -07002853#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
2854 cpu = tick_do_timer_cpu;
2855 if (cpu >= 0 && cpu < nr_cpu_ids && raw_smp_processor_id() != cpu)
Paul E. McKenney5057f55e52014-04-01 11:20:36 -07002856 set_cpus_allowed_ptr(current, cpumask_of(cpu));
Paul E. McKenneyc0f489d2014-06-04 13:46:03 -07002857#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
2858 if (!is_housekeeping_cpu(raw_smp_processor_id()))
2859 housekeeping_affine(current);
2860#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
Paul E. McKenney5057f55e52014-04-01 11:20:36 -07002861}