Merge tag 'sound-3.11' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound
[linux-2.6.git] / kernel / rcutiny.c
blobaa344111de3efdf67777bf6be400a5d2018b22c0
1 /*
2 * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
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.
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.
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.
18 * Copyright IBM Corporation, 2008
20 * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
22 * For detailed explanation of Read-Copy Update mechanism see -
23 * Documentation/RCU
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>
39 #ifdef CONFIG_RCU_TRACE
40 #include <trace/events/rcu.h>
41 #endif /* #else #ifdef CONFIG_RCU_TRACE */
43 #include "rcu.h"
45 /* Forward declarations for rcutiny_plugin.h. */
46 struct rcu_ctrlblk;
47 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp);
48 static void rcu_process_callbacks(struct softirq_action *unused);
49 static void __call_rcu(struct rcu_head *head,
50 void (*func)(struct rcu_head *rcu),
51 struct rcu_ctrlblk *rcp);
53 static long long rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
55 #include "rcutiny_plugin.h"
57 /* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */
58 static void rcu_idle_enter_common(long long newval)
60 if (newval) {
61 RCU_TRACE(trace_rcu_dyntick("--=",
62 rcu_dynticks_nesting, newval));
63 rcu_dynticks_nesting = newval;
64 return;
66 RCU_TRACE(trace_rcu_dyntick("Start", rcu_dynticks_nesting, newval));
67 if (!is_idle_task(current)) {
68 struct task_struct *idle = idle_task(smp_processor_id());
70 RCU_TRACE(trace_rcu_dyntick("Error on entry: not idle task",
71 rcu_dynticks_nesting, newval));
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! */
77 rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
78 barrier();
79 rcu_dynticks_nesting = newval;
83 * Enter idle, which is an extended quiescent state if we have fully
84 * entered that mode (i.e., if the new value of dynticks_nesting is zero).
86 void rcu_idle_enter(void)
88 unsigned long flags;
89 long long newval;
91 local_irq_save(flags);
92 WARN_ON_ONCE((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0);
93 if ((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) ==
94 DYNTICK_TASK_NEST_VALUE)
95 newval = 0;
96 else
97 newval = rcu_dynticks_nesting - DYNTICK_TASK_NEST_VALUE;
98 rcu_idle_enter_common(newval);
99 local_irq_restore(flags);
101 EXPORT_SYMBOL_GPL(rcu_idle_enter);
104 * Exit an interrupt handler towards idle.
106 void rcu_irq_exit(void)
108 unsigned long flags;
109 long long newval;
111 local_irq_save(flags);
112 newval = rcu_dynticks_nesting - 1;
113 WARN_ON_ONCE(newval < 0);
114 rcu_idle_enter_common(newval);
115 local_irq_restore(flags);
117 EXPORT_SYMBOL_GPL(rcu_irq_exit);
119 /* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */
120 static void rcu_idle_exit_common(long long oldval)
122 if (oldval) {
123 RCU_TRACE(trace_rcu_dyntick("++=",
124 oldval, rcu_dynticks_nesting));
125 return;
127 RCU_TRACE(trace_rcu_dyntick("End", oldval, rcu_dynticks_nesting));
128 if (!is_idle_task(current)) {
129 struct task_struct *idle = idle_task(smp_processor_id());
131 RCU_TRACE(trace_rcu_dyntick("Error on exit: not idle task",
132 oldval, rcu_dynticks_nesting));
133 ftrace_dump(DUMP_ALL);
134 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
135 current->pid, current->comm,
136 idle->pid, idle->comm); /* must be idle task! */
141 * Exit idle, so that we are no longer in an extended quiescent state.
143 void rcu_idle_exit(void)
145 unsigned long flags;
146 long long oldval;
148 local_irq_save(flags);
149 oldval = rcu_dynticks_nesting;
150 WARN_ON_ONCE(rcu_dynticks_nesting < 0);
151 if (rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK)
152 rcu_dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
153 else
154 rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
155 rcu_idle_exit_common(oldval);
156 local_irq_restore(flags);
158 EXPORT_SYMBOL_GPL(rcu_idle_exit);
161 * Enter an interrupt handler, moving away from idle.
163 void rcu_irq_enter(void)
165 unsigned long flags;
166 long long oldval;
168 local_irq_save(flags);
169 oldval = rcu_dynticks_nesting;
170 rcu_dynticks_nesting++;
171 WARN_ON_ONCE(rcu_dynticks_nesting == 0);
172 rcu_idle_exit_common(oldval);
173 local_irq_restore(flags);
175 EXPORT_SYMBOL_GPL(rcu_irq_enter);
177 #ifdef CONFIG_DEBUG_LOCK_ALLOC
180 * Test whether RCU thinks that the current CPU is idle.
182 int rcu_is_cpu_idle(void)
184 return !rcu_dynticks_nesting;
186 EXPORT_SYMBOL(rcu_is_cpu_idle);
188 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
191 * Test whether the current CPU was interrupted from idle. Nested
192 * interrupts don't count, we must be running at the first interrupt
193 * level.
195 static int rcu_is_cpu_rrupt_from_idle(void)
197 return rcu_dynticks_nesting <= 1;
201 * Helper function for rcu_sched_qs() and rcu_bh_qs().
202 * Also irqs are disabled to avoid confusion due to interrupt handlers
203 * invoking call_rcu().
205 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
207 RCU_TRACE(reset_cpu_stall_ticks(rcp));
208 if (rcp->rcucblist != NULL &&
209 rcp->donetail != rcp->curtail) {
210 rcp->donetail = rcp->curtail;
211 return 1;
214 return 0;
218 * Record an rcu quiescent state. And an rcu_bh quiescent state while we
219 * are at it, given that any rcu quiescent state is also an rcu_bh
220 * quiescent state. Use "+" instead of "||" to defeat short circuiting.
222 void rcu_sched_qs(int cpu)
224 unsigned long flags;
226 local_irq_save(flags);
227 if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
228 rcu_qsctr_help(&rcu_bh_ctrlblk))
229 raise_softirq(RCU_SOFTIRQ);
230 local_irq_restore(flags);
234 * Record an rcu_bh quiescent state.
236 void rcu_bh_qs(int cpu)
238 unsigned long flags;
240 local_irq_save(flags);
241 if (rcu_qsctr_help(&rcu_bh_ctrlblk))
242 raise_softirq(RCU_SOFTIRQ);
243 local_irq_restore(flags);
247 * Check to see if the scheduling-clock interrupt came from an extended
248 * quiescent state, and, if so, tell RCU about it. This function must
249 * be called from hardirq context. It is normally called from the
250 * scheduling-clock interrupt.
252 void rcu_check_callbacks(int cpu, int user)
254 RCU_TRACE(check_cpu_stalls());
255 if (user || rcu_is_cpu_rrupt_from_idle())
256 rcu_sched_qs(cpu);
257 else if (!in_softirq())
258 rcu_bh_qs(cpu);
262 * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
263 * whose grace period has elapsed.
265 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
267 char *rn = NULL;
268 struct rcu_head *next, *list;
269 unsigned long flags;
270 RCU_TRACE(int cb_count = 0);
272 /* If no RCU callbacks ready to invoke, just return. */
273 if (&rcp->rcucblist == rcp->donetail) {
274 RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, 0, -1));
275 RCU_TRACE(trace_rcu_batch_end(rcp->name, 0,
276 ACCESS_ONCE(rcp->rcucblist),
277 need_resched(),
278 is_idle_task(current),
279 false));
280 return;
283 /* Move the ready-to-invoke callbacks to a local list. */
284 local_irq_save(flags);
285 RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1));
286 list = rcp->rcucblist;
287 rcp->rcucblist = *rcp->donetail;
288 *rcp->donetail = NULL;
289 if (rcp->curtail == rcp->donetail)
290 rcp->curtail = &rcp->rcucblist;
291 rcp->donetail = &rcp->rcucblist;
292 local_irq_restore(flags);
294 /* Invoke the callbacks on the local list. */
295 RCU_TRACE(rn = rcp->name);
296 while (list) {
297 next = list->next;
298 prefetch(next);
299 debug_rcu_head_unqueue(list);
300 local_bh_disable();
301 __rcu_reclaim(rn, list);
302 local_bh_enable();
303 list = next;
304 RCU_TRACE(cb_count++);
306 RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
307 RCU_TRACE(trace_rcu_batch_end(rcp->name, cb_count, 0, need_resched(),
308 is_idle_task(current),
309 false));
312 static void rcu_process_callbacks(struct softirq_action *unused)
314 __rcu_process_callbacks(&rcu_sched_ctrlblk);
315 __rcu_process_callbacks(&rcu_bh_ctrlblk);
319 * Wait for a grace period to elapse. But it is illegal to invoke
320 * synchronize_sched() from within an RCU read-side critical section.
321 * Therefore, any legal call to synchronize_sched() is a quiescent
322 * state, and so on a UP system, synchronize_sched() need do nothing.
323 * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the
324 * benefits of doing might_sleep() to reduce latency.)
326 * Cool, huh? (Due to Josh Triplett.)
328 * But we want to make this a static inline later. The cond_resched()
329 * currently makes this problematic.
331 void synchronize_sched(void)
333 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
334 !lock_is_held(&rcu_lock_map) &&
335 !lock_is_held(&rcu_sched_lock_map),
336 "Illegal synchronize_sched() in RCU read-side critical section");
337 cond_resched();
339 EXPORT_SYMBOL_GPL(synchronize_sched);
342 * Helper function for call_rcu() and call_rcu_bh().
344 static void __call_rcu(struct rcu_head *head,
345 void (*func)(struct rcu_head *rcu),
346 struct rcu_ctrlblk *rcp)
348 unsigned long flags;
350 debug_rcu_head_queue(head);
351 head->func = func;
352 head->next = NULL;
354 local_irq_save(flags);
355 *rcp->curtail = head;
356 rcp->curtail = &head->next;
357 RCU_TRACE(rcp->qlen++);
358 local_irq_restore(flags);
362 * Post an RCU callback to be invoked after the end of an RCU-sched grace
363 * period. But since we have but one CPU, that would be after any
364 * quiescent state.
366 void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
368 __call_rcu(head, func, &rcu_sched_ctrlblk);
370 EXPORT_SYMBOL_GPL(call_rcu_sched);
373 * Post an RCU bottom-half callback to be invoked after any subsequent
374 * quiescent state.
376 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
378 __call_rcu(head, func, &rcu_bh_ctrlblk);
380 EXPORT_SYMBOL_GPL(call_rcu_bh);
382 void rcu_init(void)
384 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);