2 * Read-Copy Update mechanism for mutual exclusion
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, 2001
20 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
21 * Manfred Spraul <manfred@colorfullife.com>
23 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
24 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
26 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
27 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
29 * For detailed explanation of Read-Copy Update mechanism see -
30 * http://lse.sourceforge.net/locking/rcupdate.html
33 #include <linux/types.h>
34 #include <linux/kernel.h>
35 #include <linux/init.h>
36 #include <linux/spinlock.h>
37 #include <linux/smp.h>
38 #include <linux/interrupt.h>
39 #include <linux/sched.h>
40 #include <linux/atomic.h>
41 #include <linux/bitops.h>
42 #include <linux/percpu.h>
43 #include <linux/notifier.h>
44 #include <linux/cpu.h>
45 #include <linux/mutex.h>
46 #include <linux/export.h>
47 #include <linux/hardirq.h>
48 #include <linux/delay.h>
49 #include <linux/module.h>
51 #define CREATE_TRACE_POINTS
52 #include <trace/events/rcu.h>
56 module_param(rcu_expedited, int, 0);
58 #ifdef CONFIG_PREEMPT_RCU
61 * Preemptible RCU implementation for rcu_read_lock().
62 * Just increment ->rcu_read_lock_nesting, shared state will be updated
65 void __rcu_read_lock(void)
67 current->rcu_read_lock_nesting++;
68 barrier(); /* critical section after entry code. */
70 EXPORT_SYMBOL_GPL(__rcu_read_lock);
73 * Preemptible RCU implementation for rcu_read_unlock().
74 * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
75 * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
76 * invoke rcu_read_unlock_special() to clean up after a context switch
77 * in an RCU read-side critical section and other special cases.
79 void __rcu_read_unlock(void)
81 struct task_struct *t = current;
83 if (t->rcu_read_lock_nesting != 1) {
84 --t->rcu_read_lock_nesting;
86 barrier(); /* critical section before exit code. */
87 t->rcu_read_lock_nesting = INT_MIN;
88 #ifdef CONFIG_PROVE_RCU_DELAY
89 udelay(10); /* Make preemption more probable. */
90 #endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
91 barrier(); /* assign before ->rcu_read_unlock_special load */
92 if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
93 rcu_read_unlock_special(t);
94 barrier(); /* ->rcu_read_unlock_special load before assign */
95 t->rcu_read_lock_nesting = 0;
97 #ifdef CONFIG_PROVE_LOCKING
99 int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);
101 WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
103 #endif /* #ifdef CONFIG_PROVE_LOCKING */
105 EXPORT_SYMBOL_GPL(__rcu_read_unlock);
107 #endif /* #ifdef CONFIG_PREEMPT_RCU */
109 #ifdef CONFIG_DEBUG_LOCK_ALLOC
110 static struct lock_class_key rcu_lock_key;
111 struct lockdep_map rcu_lock_map =
112 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
113 EXPORT_SYMBOL_GPL(rcu_lock_map);
115 static struct lock_class_key rcu_bh_lock_key;
116 struct lockdep_map rcu_bh_lock_map =
117 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
118 EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
120 static struct lock_class_key rcu_sched_lock_key;
121 struct lockdep_map rcu_sched_lock_map =
122 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
123 EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
126 #ifdef CONFIG_DEBUG_LOCK_ALLOC
128 int debug_lockdep_rcu_enabled(void)
130 return rcu_scheduler_active && debug_locks &&
131 current->lockdep_recursion == 0;
133 EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
136 * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
138 * Check for bottom half being disabled, which covers both the
139 * CONFIG_PROVE_RCU and not cases. Note that if someone uses
140 * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
141 * will show the situation. This is useful for debug checks in functions
142 * that require that they be called within an RCU read-side critical
145 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
147 * Note that rcu_read_lock() is disallowed if the CPU is either idle or
148 * offline from an RCU perspective, so check for those as well.
150 int rcu_read_lock_bh_held(void)
152 if (!debug_lockdep_rcu_enabled())
154 if (rcu_is_cpu_idle())
156 if (!rcu_lockdep_current_cpu_online())
158 return in_softirq() || irqs_disabled();
160 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
162 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
164 struct rcu_synchronize {
165 struct rcu_head head;
166 struct completion completion;
170 * Awaken the corresponding synchronize_rcu() instance now that a
171 * grace period has elapsed.
173 static void wakeme_after_rcu(struct rcu_head *head)
175 struct rcu_synchronize *rcu;
177 rcu = container_of(head, struct rcu_synchronize, head);
178 complete(&rcu->completion);
181 void wait_rcu_gp(call_rcu_func_t crf)
183 struct rcu_synchronize rcu;
185 init_rcu_head_on_stack(&rcu.head);
186 init_completion(&rcu.completion);
187 /* Will wake me after RCU finished. */
188 crf(&rcu.head, wakeme_after_rcu);
190 wait_for_completion(&rcu.completion);
191 destroy_rcu_head_on_stack(&rcu.head);
193 EXPORT_SYMBOL_GPL(wait_rcu_gp);
195 #ifdef CONFIG_PROVE_RCU
197 * wrapper function to avoid #include problems.
199 int rcu_my_thread_group_empty(void)
201 return thread_group_empty(current);
203 EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
204 #endif /* #ifdef CONFIG_PROVE_RCU */
206 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
207 static inline void debug_init_rcu_head(struct rcu_head *head)
209 debug_object_init(head, &rcuhead_debug_descr);
212 static inline void debug_rcu_head_free(struct rcu_head *head)
214 debug_object_free(head, &rcuhead_debug_descr);
218 * fixup_init is called when:
219 * - an active object is initialized
221 static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
223 struct rcu_head *head = addr;
226 case ODEBUG_STATE_ACTIVE:
228 * Ensure that queued callbacks are all executed.
229 * If we detect that we are nested in a RCU read-side critical
230 * section, we should simply fail, otherwise we would deadlock.
231 * In !PREEMPT configurations, there is no way to tell if we are
232 * in a RCU read-side critical section or not, so we never
233 * attempt any fixup and just print a warning.
235 #ifndef CONFIG_PREEMPT
239 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
247 debug_object_init(head, &rcuhead_debug_descr);
255 * fixup_activate is called when:
256 * - an active object is activated
257 * - an unknown object is activated (might be a statically initialized object)
258 * Activation is performed internally by call_rcu().
260 static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
262 struct rcu_head *head = addr;
266 case ODEBUG_STATE_NOTAVAILABLE:
268 * This is not really a fixup. We just make sure that it is
269 * tracked in the object tracker.
271 debug_object_init(head, &rcuhead_debug_descr);
272 debug_object_activate(head, &rcuhead_debug_descr);
275 case ODEBUG_STATE_ACTIVE:
277 * Ensure that queued callbacks are all executed.
278 * If we detect that we are nested in a RCU read-side critical
279 * section, we should simply fail, otherwise we would deadlock.
280 * In !PREEMPT configurations, there is no way to tell if we are
281 * in a RCU read-side critical section or not, so we never
282 * attempt any fixup and just print a warning.
284 #ifndef CONFIG_PREEMPT
288 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
296 debug_object_activate(head, &rcuhead_debug_descr);
304 * fixup_free is called when:
305 * - an active object is freed
307 static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
309 struct rcu_head *head = addr;
312 case ODEBUG_STATE_ACTIVE:
314 * Ensure that queued callbacks are all executed.
315 * If we detect that we are nested in a RCU read-side critical
316 * section, we should simply fail, otherwise we would deadlock.
317 * In !PREEMPT configurations, there is no way to tell if we are
318 * in a RCU read-side critical section or not, so we never
319 * attempt any fixup and just print a warning.
321 #ifndef CONFIG_PREEMPT
325 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
333 debug_object_free(head, &rcuhead_debug_descr);
341 * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
342 * @head: pointer to rcu_head structure to be initialized
344 * This function informs debugobjects of a new rcu_head structure that
345 * has been allocated as an auto variable on the stack. This function
346 * is not required for rcu_head structures that are statically defined or
347 * that are dynamically allocated on the heap. This function has no
348 * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
350 void init_rcu_head_on_stack(struct rcu_head *head)
352 debug_object_init_on_stack(head, &rcuhead_debug_descr);
354 EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
357 * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
358 * @head: pointer to rcu_head structure to be initialized
360 * This function informs debugobjects that an on-stack rcu_head structure
361 * is about to go out of scope. As with init_rcu_head_on_stack(), this
362 * function is not required for rcu_head structures that are statically
363 * defined or that are dynamically allocated on the heap. Also as with
364 * init_rcu_head_on_stack(), this function has no effect for
365 * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
367 void destroy_rcu_head_on_stack(struct rcu_head *head)
369 debug_object_free(head, &rcuhead_debug_descr);
371 EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
373 struct debug_obj_descr rcuhead_debug_descr = {
375 .fixup_init = rcuhead_fixup_init,
376 .fixup_activate = rcuhead_fixup_activate,
377 .fixup_free = rcuhead_fixup_free,
379 EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
380 #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
382 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
383 void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp,
385 unsigned long c_old, unsigned long c)
387 trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c);
389 EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
391 #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
395 #ifdef CONFIG_RCU_STALL_COMMON
397 #ifdef CONFIG_PROVE_RCU
398 #define RCU_STALL_DELAY_DELTA (5 * HZ)
400 #define RCU_STALL_DELAY_DELTA 0
403 int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */
404 int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
406 module_param(rcu_cpu_stall_suppress, int, 0644);
407 module_param(rcu_cpu_stall_timeout, int, 0644);
409 int rcu_jiffies_till_stall_check(void)
411 int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout);
414 * Limit check must be consistent with the Kconfig limits
415 * for CONFIG_RCU_CPU_STALL_TIMEOUT.
417 if (till_stall_check < 3) {
418 ACCESS_ONCE(rcu_cpu_stall_timeout) = 3;
419 till_stall_check = 3;
420 } else if (till_stall_check > 300) {
421 ACCESS_ONCE(rcu_cpu_stall_timeout) = 300;
422 till_stall_check = 300;
424 return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
427 static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
429 rcu_cpu_stall_suppress = 1;
433 static struct notifier_block rcu_panic_block = {
434 .notifier_call = rcu_panic,
437 static int __init check_cpu_stall_init(void)
439 atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
442 early_initcall(check_cpu_stall_init);
444 #endif /* #ifdef CONFIG_RCU_STALL_COMMON */