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 * Author: Dipankar Sarma <dipankar@in.ibm.com>
22 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
23 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
25 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
26 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
28 * For detailed explanation of Read-Copy Update mechanism see -
29 * http://lse.sourceforge.net/locking/rcupdate.html
33 #ifndef __LINUX_RCUPDATE_H
34 #define __LINUX_RCUPDATE_H
36 #include <linux/cache.h>
37 #include <linux/spinlock.h>
38 #include <linux/threads.h>
39 #include <linux/cpumask.h>
40 #include <linux/seqlock.h>
41 #include <linux/lockdep.h>
42 #include <linux/completion.h>
44 #ifdef CONFIG_RCU_TORTURE_TEST
45 extern int rcutorture_runnable; /* for sysctl */
46 #endif /* #ifdef CONFIG_RCU_TORTURE_TEST */
49 * struct rcu_head - callback structure for use with RCU
50 * @next: next update requests in a list
51 * @func: actual update function to call after the grace period.
54 struct rcu_head *next;
55 void (*func)(struct rcu_head *head);
58 /* Exported common interfaces */
59 extern void synchronize_rcu_bh(void);
60 extern void synchronize_sched(void);
61 extern void rcu_barrier(void);
62 extern void rcu_barrier_bh(void);
63 extern void rcu_barrier_sched(void);
64 extern void synchronize_sched_expedited(void);
65 extern int sched_expedited_torture_stats(char *page);
67 /* Internal to kernel */
68 extern void rcu_init(void);
69 extern int rcu_scheduler_active;
70 extern void rcu_scheduler_starting(void);
72 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
73 #include <linux/rcutree.h>
74 #elif defined(CONFIG_TINY_RCU)
75 #include <linux/rcutiny.h>
77 #error "Unknown RCU implementation specified to kernel configuration"
80 #define RCU_HEAD_INIT { .next = NULL, .func = NULL }
81 #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
82 #define INIT_RCU_HEAD(ptr) do { \
83 (ptr)->next = NULL; (ptr)->func = NULL; \
86 #ifdef CONFIG_DEBUG_LOCK_ALLOC
88 extern struct lockdep_map rcu_lock_map;
89 # define rcu_read_acquire() \
90 lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
91 # define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_)
93 extern struct lockdep_map rcu_bh_lock_map;
94 # define rcu_read_acquire_bh() \
95 lock_acquire(&rcu_bh_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
96 # define rcu_read_release_bh() lock_release(&rcu_bh_lock_map, 1, _THIS_IP_)
98 extern struct lockdep_map rcu_sched_lock_map;
99 # define rcu_read_acquire_sched() \
100 lock_acquire(&rcu_sched_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
101 # define rcu_read_release_sched() \
102 lock_release(&rcu_sched_lock_map, 1, _THIS_IP_)
104 static inline int debug_lockdep_rcu_enabled(void)
106 return likely(rcu_scheduler_active && debug_locks);
110 * rcu_read_lock_held - might we be in RCU read-side critical section?
112 * If CONFIG_PROVE_LOCKING is selected and enabled, returns nonzero iff in
113 * an RCU read-side critical section. In absence of CONFIG_PROVE_LOCKING,
114 * this assumes we are in an RCU read-side critical section unless it can
117 * Check rcu_scheduler_active to prevent false positives during boot.
119 static inline int rcu_read_lock_held(void)
121 if (!debug_lockdep_rcu_enabled())
123 return lock_is_held(&rcu_lock_map);
127 * rcu_read_lock_bh_held() is defined out of line to avoid #include-file
130 extern int rcu_read_lock_bh_held(void);
133 * rcu_read_lock_sched_held - might we be in RCU-sched read-side critical section?
135 * If CONFIG_PROVE_LOCKING is selected and enabled, returns nonzero iff in an
136 * RCU-sched read-side critical section. In absence of CONFIG_PROVE_LOCKING,
137 * this assumes we are in an RCU-sched read-side critical section unless it
138 * can prove otherwise. Note that disabling of preemption (including
139 * disabling irqs) counts as an RCU-sched read-side critical section.
141 * Check rcu_scheduler_active to prevent false positives during boot.
143 #ifdef CONFIG_PREEMPT
144 static inline int rcu_read_lock_sched_held(void)
146 int lockdep_opinion = 0;
148 if (!debug_lockdep_rcu_enabled())
151 lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
152 return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
154 #else /* #ifdef CONFIG_PREEMPT */
155 static inline int rcu_read_lock_sched_held(void)
159 #endif /* #else #ifdef CONFIG_PREEMPT */
161 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
163 # define rcu_read_acquire() do { } while (0)
164 # define rcu_read_release() do { } while (0)
165 # define rcu_read_acquire_bh() do { } while (0)
166 # define rcu_read_release_bh() do { } while (0)
167 # define rcu_read_acquire_sched() do { } while (0)
168 # define rcu_read_release_sched() do { } while (0)
170 static inline int rcu_read_lock_held(void)
175 static inline int rcu_read_lock_bh_held(void)
180 #ifdef CONFIG_PREEMPT
181 static inline int rcu_read_lock_sched_held(void)
183 return !rcu_scheduler_active || preempt_count() != 0 || irqs_disabled();
185 #else /* #ifdef CONFIG_PREEMPT */
186 static inline int rcu_read_lock_sched_held(void)
190 #endif /* #else #ifdef CONFIG_PREEMPT */
192 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
194 #ifdef CONFIG_PROVE_RCU
197 * rcu_dereference_check - rcu_dereference with debug checking
198 * @p: The pointer to read, prior to dereferencing
199 * @c: The conditions under which the dereference will take place
201 * Do an rcu_dereference(), but check that the conditions under which the
202 * dereference will take place are correct. Typically the conditions indicate
203 * the various locking conditions that should be held at that point. The check
204 * should return true if the conditions are satisfied.
208 * bar = rcu_dereference_check(foo->bar, rcu_read_lock_held() ||
209 * lockdep_is_held(&foo->lock));
211 * could be used to indicate to lockdep that foo->bar may only be dereferenced
212 * if either the RCU read lock is held, or that the lock required to replace
213 * the bar struct at foo->bar is held.
215 * Note that the list of conditions may also include indications of when a lock
216 * need not be held, for example during initialisation or destruction of the
219 * bar = rcu_dereference_check(foo->bar, rcu_read_lock_held() ||
220 * lockdep_is_held(&foo->lock) ||
221 * atomic_read(&foo->usage) == 0);
223 #define rcu_dereference_check(p, c) \
225 if (debug_lockdep_rcu_enabled() && !(c)) \
226 lockdep_rcu_dereference(__FILE__, __LINE__); \
227 rcu_dereference_raw(p); \
231 * rcu_dereference_protected - fetch RCU pointer when updates prevented
233 * Return the value of the specified RCU-protected pointer, but omit
234 * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This
235 * is useful in cases where update-side locks prevent the value of the
236 * pointer from changing. Please note that this primitive does -not-
237 * prevent the compiler from repeating this reference or combining it
238 * with other references, so it should not be used without protection
239 * of appropriate locks.
241 #define rcu_dereference_protected(p, c) \
243 if (debug_lockdep_rcu_enabled() && !(c)) \
244 lockdep_rcu_dereference(__FILE__, __LINE__); \
248 #else /* #ifdef CONFIG_PROVE_RCU */
250 #define rcu_dereference_check(p, c) rcu_dereference_raw(p)
251 #define rcu_dereference_protected(p, c) (p)
253 #endif /* #else #ifdef CONFIG_PROVE_RCU */
256 * rcu_access_pointer - fetch RCU pointer with no dereferencing
258 * Return the value of the specified RCU-protected pointer, but omit the
259 * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful
260 * when the value of this pointer is accessed, but the pointer is not
261 * dereferenced, for example, when testing an RCU-protected pointer against
262 * NULL. This may also be used in cases where update-side locks prevent
263 * the value of the pointer from changing, but rcu_dereference_protected()
264 * is a lighter-weight primitive for this use case.
266 #define rcu_access_pointer(p) ACCESS_ONCE(p)
269 * rcu_read_lock - mark the beginning of an RCU read-side critical section.
271 * When synchronize_rcu() is invoked on one CPU while other CPUs
272 * are within RCU read-side critical sections, then the
273 * synchronize_rcu() is guaranteed to block until after all the other
274 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
275 * on one CPU while other CPUs are within RCU read-side critical
276 * sections, invocation of the corresponding RCU callback is deferred
277 * until after the all the other CPUs exit their critical sections.
279 * Note, however, that RCU callbacks are permitted to run concurrently
280 * with RCU read-side critical sections. One way that this can happen
281 * is via the following sequence of events: (1) CPU 0 enters an RCU
282 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
283 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
284 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
285 * callback is invoked. This is legal, because the RCU read-side critical
286 * section that was running concurrently with the call_rcu() (and which
287 * therefore might be referencing something that the corresponding RCU
288 * callback would free up) has completed before the corresponding
289 * RCU callback is invoked.
291 * RCU read-side critical sections may be nested. Any deferred actions
292 * will be deferred until the outermost RCU read-side critical section
295 * It is illegal to block while in an RCU read-side critical section.
297 static inline void rcu_read_lock(void)
305 * So where is rcu_write_lock()? It does not exist, as there is no
306 * way for writers to lock out RCU readers. This is a feature, not
307 * a bug -- this property is what provides RCU's performance benefits.
308 * Of course, writers must coordinate with each other. The normal
309 * spinlock primitives work well for this, but any other technique may be
310 * used as well. RCU does not care how the writers keep out of each
311 * others' way, as long as they do so.
315 * rcu_read_unlock - marks the end of an RCU read-side critical section.
317 * See rcu_read_lock() for more information.
319 static inline void rcu_read_unlock(void)
327 * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
329 * This is equivalent of rcu_read_lock(), but to be used when updates
330 * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
331 * consider completion of a softirq handler to be a quiescent state,
332 * a process in RCU read-side critical section must be protected by
333 * disabling softirqs. Read-side critical sections in interrupt context
334 * can use just rcu_read_lock().
337 static inline void rcu_read_lock_bh(void)
339 __rcu_read_lock_bh();
341 rcu_read_acquire_bh();
345 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
347 * See rcu_read_lock_bh() for more information.
349 static inline void rcu_read_unlock_bh(void)
351 rcu_read_release_bh();
353 __rcu_read_unlock_bh();
357 * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
359 * Should be used with either
360 * - synchronize_sched()
362 * - call_rcu_sched() and rcu_barrier_sched()
363 * on the write-side to insure proper synchronization.
365 static inline void rcu_read_lock_sched(void)
368 __acquire(RCU_SCHED);
369 rcu_read_acquire_sched();
372 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
373 static inline notrace void rcu_read_lock_sched_notrace(void)
375 preempt_disable_notrace();
376 __acquire(RCU_SCHED);
380 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
382 * See rcu_read_lock_sched for more information.
384 static inline void rcu_read_unlock_sched(void)
386 rcu_read_release_sched();
387 __release(RCU_SCHED);
391 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
392 static inline notrace void rcu_read_unlock_sched_notrace(void)
394 __release(RCU_SCHED);
395 preempt_enable_notrace();
400 * rcu_dereference_raw - fetch an RCU-protected pointer
402 * The caller must be within some flavor of RCU read-side critical
403 * section, or must be otherwise preventing the pointer from changing,
404 * for example, by holding an appropriate lock. This pointer may later
405 * be safely dereferenced. It is the caller's responsibility to have
406 * done the right thing, as this primitive does no checking of any kind.
408 * Inserts memory barriers on architectures that require them
409 * (currently only the Alpha), and, more importantly, documents
410 * exactly which pointers are protected by RCU.
412 #define rcu_dereference_raw(p) ({ \
413 typeof(p) _________p1 = ACCESS_ONCE(p); \
414 smp_read_barrier_depends(); \
419 * rcu_dereference - fetch an RCU-protected pointer, checking for RCU
421 * Makes rcu_dereference_check() do the dirty work.
423 #define rcu_dereference(p) \
424 rcu_dereference_check(p, rcu_read_lock_held())
427 * rcu_dereference_bh - fetch an RCU-protected pointer, checking for RCU-bh
429 * Makes rcu_dereference_check() do the dirty work.
431 #define rcu_dereference_bh(p) \
432 rcu_dereference_check(p, rcu_read_lock_bh_held())
435 * rcu_dereference_sched - fetch RCU-protected pointer, checking for RCU-sched
437 * Makes rcu_dereference_check() do the dirty work.
439 #define rcu_dereference_sched(p) \
440 rcu_dereference_check(p, rcu_read_lock_sched_held())
443 * rcu_assign_pointer - assign (publicize) a pointer to a newly
444 * initialized structure that will be dereferenced by RCU read-side
445 * critical sections. Returns the value assigned.
447 * Inserts memory barriers on architectures that require them
448 * (pretty much all of them other than x86), and also prevents
449 * the compiler from reordering the code that initializes the
450 * structure after the pointer assignment. More importantly, this
451 * call documents which pointers will be dereferenced by RCU read-side
455 #define rcu_assign_pointer(p, v) \
457 if (!__builtin_constant_p(v) || \
463 /* Infrastructure to implement the synchronize_() primitives. */
465 struct rcu_synchronize {
466 struct rcu_head head;
467 struct completion completion;
470 extern void wakeme_after_rcu(struct rcu_head *head);
473 * call_rcu - Queue an RCU callback for invocation after a grace period.
474 * @head: structure to be used for queueing the RCU updates.
475 * @func: actual update function to be invoked after the grace period
477 * The update function will be invoked some time after a full grace
478 * period elapses, in other words after all currently executing RCU
479 * read-side critical sections have completed. RCU read-side critical
480 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
483 extern void call_rcu(struct rcu_head *head,
484 void (*func)(struct rcu_head *head));
487 * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
488 * @head: structure to be used for queueing the RCU updates.
489 * @func: actual update function to be invoked after the grace period
491 * The update function will be invoked some time after a full grace
492 * period elapses, in other words after all currently executing RCU
493 * read-side critical sections have completed. call_rcu_bh() assumes
494 * that the read-side critical sections end on completion of a softirq
495 * handler. This means that read-side critical sections in process
496 * context must not be interrupted by softirqs. This interface is to be
497 * used when most of the read-side critical sections are in softirq context.
498 * RCU read-side critical sections are delimited by :
499 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
501 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
502 * These may be nested.
504 extern void call_rcu_bh(struct rcu_head *head,
505 void (*func)(struct rcu_head *head));
507 #endif /* __LINUX_RCUPDATE_H */