rcu: Augment rcu_batch_end tracing for idle and callback state
[linux-3.10.git] / kernel / rcutiny.c
1 /*
2  * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
3  *
4  * This program is free software; you can redistribute it and/or modify
5  * it under the terms of the GNU General Public License as published by
6  * the Free Software Foundation; either version 2 of the License, or
7  * (at your option) any later version.
8  *
9  * This program is distributed in the hope that it will be useful,
10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12  * GNU General Public License for more details.
13  *
14  * You should have received a copy of the GNU General Public License
15  * along with this program; if not, write to the Free Software
16  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
17  *
18  * Copyright IBM Corporation, 2008
19  *
20  * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
21  *
22  * For detailed explanation of Read-Copy Update mechanism see -
23  *              Documentation/RCU
24  */
25 #include <linux/completion.h>
26 #include <linux/interrupt.h>
27 #include <linux/notifier.h>
28 #include <linux/rcupdate.h>
29 #include <linux/kernel.h>
30 #include <linux/export.h>
31 #include <linux/mutex.h>
32 #include <linux/sched.h>
33 #include <linux/types.h>
34 #include <linux/init.h>
35 #include <linux/time.h>
36 #include <linux/cpu.h>
37 #include <linux/prefetch.h>
38
39 #ifdef CONFIG_RCU_TRACE
40 #include <trace/events/rcu.h>
41 #endif /* #else #ifdef CONFIG_RCU_TRACE */
42
43 #include "rcu.h"
44
45 /* Forward declarations for rcutiny_plugin.h. */
46 struct rcu_ctrlblk;
47 static void invoke_rcu_callbacks(void);
48 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp);
49 static void rcu_process_callbacks(struct softirq_action *unused);
50 static void __call_rcu(struct rcu_head *head,
51                        void (*func)(struct rcu_head *rcu),
52                        struct rcu_ctrlblk *rcp);
53
54 #include "rcutiny_plugin.h"
55
56 static long long rcu_dynticks_nesting = DYNTICK_TASK_NESTING;
57
58 /* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */
59 static void rcu_idle_enter_common(long long oldval)
60 {
61         if (rcu_dynticks_nesting) {
62                 RCU_TRACE(trace_rcu_dyntick("--=",
63                                             oldval, rcu_dynticks_nesting));
64                 return;
65         }
66         RCU_TRACE(trace_rcu_dyntick("Start", oldval, rcu_dynticks_nesting));
67         if (!is_idle_task(current)) {
68                 struct task_struct *idle = idle_task(smp_processor_id());
69
70                 RCU_TRACE(trace_rcu_dyntick("Error on entry: not idle task",
71                                             oldval, rcu_dynticks_nesting));
72                 ftrace_dump(DUMP_ALL);
73                 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
74                           current->pid, current->comm,
75                           idle->pid, idle->comm); /* must be idle task! */
76         }
77         rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
78 }
79
80 /*
81  * Enter idle, which is an extended quiescent state if we have fully
82  * entered that mode (i.e., if the new value of dynticks_nesting is zero).
83  */
84 void rcu_idle_enter(void)
85 {
86         unsigned long flags;
87         long long oldval;
88
89         local_irq_save(flags);
90         oldval = rcu_dynticks_nesting;
91         rcu_dynticks_nesting = 0;
92         rcu_idle_enter_common(oldval);
93         local_irq_restore(flags);
94 }
95
96 /*
97  * Exit an interrupt handler towards idle.
98  */
99 void rcu_irq_exit(void)
100 {
101         unsigned long flags;
102         long long oldval;
103
104         local_irq_save(flags);
105         oldval = rcu_dynticks_nesting;
106         rcu_dynticks_nesting--;
107         WARN_ON_ONCE(rcu_dynticks_nesting < 0);
108         rcu_idle_enter_common(oldval);
109         local_irq_restore(flags);
110 }
111
112 /* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */
113 static void rcu_idle_exit_common(long long oldval)
114 {
115         if (oldval) {
116                 RCU_TRACE(trace_rcu_dyntick("++=",
117                                             oldval, rcu_dynticks_nesting));
118                 return;
119         }
120         RCU_TRACE(trace_rcu_dyntick("End", oldval, rcu_dynticks_nesting));
121         if (!is_idle_task(current)) {
122                 struct task_struct *idle = idle_task(smp_processor_id());
123
124                 RCU_TRACE(trace_rcu_dyntick("Error on exit: not idle task",
125                           oldval, rcu_dynticks_nesting));
126                 ftrace_dump(DUMP_ALL);
127                 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
128                           current->pid, current->comm,
129                           idle->pid, idle->comm); /* must be idle task! */
130         }
131 }
132
133 /*
134  * Exit idle, so that we are no longer in an extended quiescent state.
135  */
136 void rcu_idle_exit(void)
137 {
138         unsigned long flags;
139         long long oldval;
140
141         local_irq_save(flags);
142         oldval = rcu_dynticks_nesting;
143         WARN_ON_ONCE(oldval != 0);
144         rcu_dynticks_nesting = DYNTICK_TASK_NESTING;
145         rcu_idle_exit_common(oldval);
146         local_irq_restore(flags);
147 }
148
149 /*
150  * Enter an interrupt handler, moving away from idle.
151  */
152 void rcu_irq_enter(void)
153 {
154         unsigned long flags;
155         long long oldval;
156
157         local_irq_save(flags);
158         oldval = rcu_dynticks_nesting;
159         rcu_dynticks_nesting++;
160         WARN_ON_ONCE(rcu_dynticks_nesting == 0);
161         rcu_idle_exit_common(oldval);
162         local_irq_restore(flags);
163 }
164
165 #ifdef CONFIG_PROVE_RCU
166
167 /*
168  * Test whether RCU thinks that the current CPU is idle.
169  */
170 int rcu_is_cpu_idle(void)
171 {
172         return !rcu_dynticks_nesting;
173 }
174 EXPORT_SYMBOL(rcu_is_cpu_idle);
175
176 #endif /* #ifdef CONFIG_PROVE_RCU */
177
178 /*
179  * Test whether the current CPU was interrupted from idle.  Nested
180  * interrupts don't count, we must be running at the first interrupt
181  * level.
182  */
183 int rcu_is_cpu_rrupt_from_idle(void)
184 {
185         return rcu_dynticks_nesting <= 0;
186 }
187
188 /*
189  * Helper function for rcu_sched_qs() and rcu_bh_qs().
190  * Also irqs are disabled to avoid confusion due to interrupt handlers
191  * invoking call_rcu().
192  */
193 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
194 {
195         if (rcp->rcucblist != NULL &&
196             rcp->donetail != rcp->curtail) {
197                 rcp->donetail = rcp->curtail;
198                 return 1;
199         }
200
201         return 0;
202 }
203
204 /*
205  * Record an rcu quiescent state.  And an rcu_bh quiescent state while we
206  * are at it, given that any rcu quiescent state is also an rcu_bh
207  * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
208  */
209 void rcu_sched_qs(int cpu)
210 {
211         unsigned long flags;
212
213         local_irq_save(flags);
214         if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
215             rcu_qsctr_help(&rcu_bh_ctrlblk))
216                 invoke_rcu_callbacks();
217         local_irq_restore(flags);
218 }
219
220 /*
221  * Record an rcu_bh quiescent state.
222  */
223 void rcu_bh_qs(int cpu)
224 {
225         unsigned long flags;
226
227         local_irq_save(flags);
228         if (rcu_qsctr_help(&rcu_bh_ctrlblk))
229                 invoke_rcu_callbacks();
230         local_irq_restore(flags);
231 }
232
233 /*
234  * Check to see if the scheduling-clock interrupt came from an extended
235  * quiescent state, and, if so, tell RCU about it.  This function must
236  * be called from hardirq context.  It is normally called from the
237  * scheduling-clock interrupt.
238  */
239 void rcu_check_callbacks(int cpu, int user)
240 {
241         if (user || rcu_is_cpu_rrupt_from_idle())
242                 rcu_sched_qs(cpu);
243         else if (!in_softirq())
244                 rcu_bh_qs(cpu);
245         rcu_preempt_check_callbacks();
246 }
247
248 /*
249  * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
250  * whose grace period has elapsed.
251  */
252 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
253 {
254         char *rn = NULL;
255         struct rcu_head *next, *list;
256         unsigned long flags;
257         RCU_TRACE(int cb_count = 0);
258
259         /* If no RCU callbacks ready to invoke, just return. */
260         if (&rcp->rcucblist == rcp->donetail) {
261                 RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));
262                 RCU_TRACE(trace_rcu_batch_end(rcp->name, 0,
263                                               ACCESS_ONCE(rcp->rcucblist),
264                                               need_resched(),
265                                               is_idle_task(current),
266                                               rcu_is_callbacks_kthread()));
267                 return;
268         }
269
270         /* Move the ready-to-invoke callbacks to a local list. */
271         local_irq_save(flags);
272         RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));
273         list = rcp->rcucblist;
274         rcp->rcucblist = *rcp->donetail;
275         *rcp->donetail = NULL;
276         if (rcp->curtail == rcp->donetail)
277                 rcp->curtail = &rcp->rcucblist;
278         rcu_preempt_remove_callbacks(rcp);
279         rcp->donetail = &rcp->rcucblist;
280         local_irq_restore(flags);
281
282         /* Invoke the callbacks on the local list. */
283         RCU_TRACE(rn = rcp->name);
284         while (list) {
285                 next = list->next;
286                 prefetch(next);
287                 debug_rcu_head_unqueue(list);
288                 local_bh_disable();
289                 __rcu_reclaim(rn, list);
290                 local_bh_enable();
291                 list = next;
292                 RCU_TRACE(cb_count++);
293         }
294         RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
295         RCU_TRACE(trace_rcu_batch_end(rcp->name, cb_count, 0, need_resched(),
296                                       is_idle_task(current),
297                                       rcu_is_callbacks_kthread()));
298 }
299
300 static void rcu_process_callbacks(struct softirq_action *unused)
301 {
302         __rcu_process_callbacks(&rcu_sched_ctrlblk);
303         __rcu_process_callbacks(&rcu_bh_ctrlblk);
304         rcu_preempt_process_callbacks();
305 }
306
307 /*
308  * Wait for a grace period to elapse.  But it is illegal to invoke
309  * synchronize_sched() from within an RCU read-side critical section.
310  * Therefore, any legal call to synchronize_sched() is a quiescent
311  * state, and so on a UP system, synchronize_sched() need do nothing.
312  * Ditto for synchronize_rcu_bh().  (But Lai Jiangshan points out the
313  * benefits of doing might_sleep() to reduce latency.)
314  *
315  * Cool, huh?  (Due to Josh Triplett.)
316  *
317  * But we want to make this a static inline later.  The cond_resched()
318  * currently makes this problematic.
319  */
320 void synchronize_sched(void)
321 {
322         cond_resched();
323 }
324 EXPORT_SYMBOL_GPL(synchronize_sched);
325
326 /*
327  * Helper function for call_rcu() and call_rcu_bh().
328  */
329 static void __call_rcu(struct rcu_head *head,
330                        void (*func)(struct rcu_head *rcu),
331                        struct rcu_ctrlblk *rcp)
332 {
333         unsigned long flags;
334
335         debug_rcu_head_queue(head);
336         head->func = func;
337         head->next = NULL;
338
339         local_irq_save(flags);
340         *rcp->curtail = head;
341         rcp->curtail = &head->next;
342         RCU_TRACE(rcp->qlen++);
343         local_irq_restore(flags);
344 }
345
346 /*
347  * Post an RCU callback to be invoked after the end of an RCU-sched grace
348  * period.  But since we have but one CPU, that would be after any
349  * quiescent state.
350  */
351 void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
352 {
353         __call_rcu(head, func, &rcu_sched_ctrlblk);
354 }
355 EXPORT_SYMBOL_GPL(call_rcu_sched);
356
357 /*
358  * Post an RCU bottom-half callback to be invoked after any subsequent
359  * quiescent state.
360  */
361 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
362 {
363         __call_rcu(head, func, &rcu_bh_ctrlblk);
364 }
365 EXPORT_SYMBOL_GPL(call_rcu_bh);