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>
43 #include <linux/debugobjects.h>
44 #include <linux/compiler.h>
46 #ifdef CONFIG_RCU_TORTURE_TEST
47 extern int rcutorture_runnable; /* for sysctl */
48 #endif /* #ifdef CONFIG_RCU_TORTURE_TEST */
51 * struct rcu_head - callback structure for use with RCU
52 * @next: next update requests in a list
53 * @func: actual update function to call after the grace period.
56 struct rcu_head *next;
57 void (*func)(struct rcu_head *head);
60 /* Exported common interfaces */
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);
70 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
71 #include <linux/rcutree.h>
72 #elif defined(CONFIG_TINY_RCU)
73 #include <linux/rcutiny.h>
75 #error "Unknown RCU implementation specified to kernel configuration"
78 #define RCU_HEAD_INIT { .next = NULL, .func = NULL }
79 #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
80 #define INIT_RCU_HEAD(ptr) do { \
81 (ptr)->next = NULL; (ptr)->func = NULL; \
85 * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic
86 * initialization and destruction of rcu_head on the stack. rcu_head structures
87 * allocated dynamically in the heap or defined statically don't need any
90 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
91 extern void init_rcu_head_on_stack(struct rcu_head *head);
92 extern void destroy_rcu_head_on_stack(struct rcu_head *head);
93 #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
94 static inline void init_rcu_head_on_stack(struct rcu_head *head)
98 static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
101 #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
103 #ifdef CONFIG_DEBUG_LOCK_ALLOC
105 extern struct lockdep_map rcu_lock_map;
106 # define rcu_read_acquire() \
107 lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
108 # define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_)
110 extern struct lockdep_map rcu_bh_lock_map;
111 # define rcu_read_acquire_bh() \
112 lock_acquire(&rcu_bh_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
113 # define rcu_read_release_bh() lock_release(&rcu_bh_lock_map, 1, _THIS_IP_)
115 extern struct lockdep_map rcu_sched_lock_map;
116 # define rcu_read_acquire_sched() \
117 lock_acquire(&rcu_sched_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
118 # define rcu_read_release_sched() \
119 lock_release(&rcu_sched_lock_map, 1, _THIS_IP_)
121 extern int debug_lockdep_rcu_enabled(void);
124 * rcu_read_lock_held() - might we be in RCU read-side critical section?
126 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
127 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
128 * this assumes we are in an RCU read-side critical section unless it can
129 * prove otherwise. This is useful for debug checks in functions that
130 * require that they be called within an RCU read-side critical section.
132 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
133 * and while lockdep is disabled.
135 static inline int rcu_read_lock_held(void)
137 if (!debug_lockdep_rcu_enabled())
139 return lock_is_held(&rcu_lock_map);
143 * rcu_read_lock_bh_held() is defined out of line to avoid #include-file
146 extern int rcu_read_lock_bh_held(void);
149 * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
151 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
152 * RCU-sched read-side critical section. In absence of
153 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
154 * critical section unless it can prove otherwise. Note that disabling
155 * of preemption (including disabling irqs) counts as an RCU-sched
156 * read-side critical section. This is useful for debug checks in functions
157 * that required that they be called within an RCU-sched read-side
160 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
161 * and while lockdep is disabled.
163 #ifdef CONFIG_PREEMPT
164 static inline int rcu_read_lock_sched_held(void)
166 int lockdep_opinion = 0;
168 if (!debug_lockdep_rcu_enabled())
171 lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
172 return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
174 #else /* #ifdef CONFIG_PREEMPT */
175 static inline int rcu_read_lock_sched_held(void)
179 #endif /* #else #ifdef CONFIG_PREEMPT */
181 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
183 # define rcu_read_acquire() do { } while (0)
184 # define rcu_read_release() do { } while (0)
185 # define rcu_read_acquire_bh() do { } while (0)
186 # define rcu_read_release_bh() do { } while (0)
187 # define rcu_read_acquire_sched() do { } while (0)
188 # define rcu_read_release_sched() do { } while (0)
190 static inline int rcu_read_lock_held(void)
195 static inline int rcu_read_lock_bh_held(void)
200 #ifdef CONFIG_PREEMPT
201 static inline int rcu_read_lock_sched_held(void)
203 return preempt_count() != 0 || irqs_disabled();
205 #else /* #ifdef CONFIG_PREEMPT */
206 static inline int rcu_read_lock_sched_held(void)
210 #endif /* #else #ifdef CONFIG_PREEMPT */
212 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
214 #ifdef CONFIG_PROVE_RCU
216 extern int rcu_my_thread_group_empty(void);
218 #define __do_rcu_dereference_check(c) \
220 static bool __warned; \
221 if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
223 lockdep_rcu_dereference(__FILE__, __LINE__); \
227 #else /* #ifdef CONFIG_PROVE_RCU */
229 #define __do_rcu_dereference_check(c) do { } while (0)
231 #endif /* #else #ifdef CONFIG_PROVE_RCU */
234 * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
235 * and rcu_assign_pointer(). Some of these could be folded into their
236 * callers, but they are left separate in order to ease introduction of
237 * multiple flavors of pointers to match the multiple flavors of RCU
238 * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in
241 #define __rcu_access_pointer(p, space) \
243 typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
244 (void) (((typeof (*p) space *)p) == p); \
245 ((typeof(*p) __force __kernel *)(_________p1)); \
247 #define __rcu_dereference_check(p, c, space) \
249 typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
250 __do_rcu_dereference_check(c); \
251 (void) (((typeof (*p) space *)p) == p); \
252 smp_read_barrier_depends(); \
253 ((typeof(*p) __force __kernel *)(_________p1)); \
255 #define __rcu_dereference_protected(p, c, space) \
257 __do_rcu_dereference_check(c); \
258 (void) (((typeof (*p) space *)p) == p); \
259 ((typeof(*p) __force __kernel *)(p)); \
262 #define __rcu_dereference_index_check(p, c) \
264 typeof(p) _________p1 = ACCESS_ONCE(p); \
265 __do_rcu_dereference_check(c); \
266 smp_read_barrier_depends(); \
269 #define __rcu_assign_pointer(p, v, space) \
271 if (!__builtin_constant_p(v) || \
274 (p) = (typeof(*v) __force space *)(v); \
279 * rcu_access_pointer() - fetch RCU pointer with no dereferencing
280 * @p: The pointer to read
282 * Return the value of the specified RCU-protected pointer, but omit the
283 * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful
284 * when the value of this pointer is accessed, but the pointer is not
285 * dereferenced, for example, when testing an RCU-protected pointer against
286 * NULL. Although rcu_access_pointer() may also be used in cases where
287 * update-side locks prevent the value of the pointer from changing, you
288 * should instead use rcu_dereference_protected() for this use case.
290 #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
293 * rcu_dereference_check() - rcu_dereference with debug checking
294 * @p: The pointer to read, prior to dereferencing
295 * @c: The conditions under which the dereference will take place
297 * Do an rcu_dereference(), but check that the conditions under which the
298 * dereference will take place are correct. Typically the conditions
299 * indicate the various locking conditions that should be held at that
300 * point. The check should return true if the conditions are satisfied.
301 * An implicit check for being in an RCU read-side critical section
302 * (rcu_read_lock()) is included.
306 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
308 * could be used to indicate to lockdep that foo->bar may only be dereferenced
309 * if either rcu_read_lock() is held, or that the lock required to replace
310 * the bar struct at foo->bar is held.
312 * Note that the list of conditions may also include indications of when a lock
313 * need not be held, for example during initialisation or destruction of the
316 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
317 * atomic_read(&foo->usage) == 0);
319 * Inserts memory barriers on architectures that require them
320 * (currently only the Alpha), prevents the compiler from refetching
321 * (and from merging fetches), and, more importantly, documents exactly
322 * which pointers are protected by RCU and checks that the pointer is
323 * annotated as __rcu.
325 #define rcu_dereference_check(p, c) \
326 __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)
329 * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
330 * @p: The pointer to read, prior to dereferencing
331 * @c: The conditions under which the dereference will take place
333 * This is the RCU-bh counterpart to rcu_dereference_check().
335 #define rcu_dereference_bh_check(p, c) \
336 __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu)
339 * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
340 * @p: The pointer to read, prior to dereferencing
341 * @c: The conditions under which the dereference will take place
343 * This is the RCU-sched counterpart to rcu_dereference_check().
345 #define rcu_dereference_sched_check(p, c) \
346 __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \
349 #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/
352 * rcu_dereference_index_check() - rcu_dereference for indices with debug checking
353 * @p: The pointer to read, prior to dereferencing
354 * @c: The conditions under which the dereference will take place
356 * Similar to rcu_dereference_check(), but omits the sparse checking.
357 * This allows rcu_dereference_index_check() to be used on integers,
358 * which can then be used as array indices. Attempting to use
359 * rcu_dereference_check() on an integer will give compiler warnings
360 * because the sparse address-space mechanism relies on dereferencing
361 * the RCU-protected pointer. Dereferencing integers is not something
362 * that even gcc will put up with.
364 * Note that this function does not implicitly check for RCU read-side
365 * critical sections. If this function gains lots of uses, it might
366 * make sense to provide versions for each flavor of RCU, but it does
367 * not make sense as of early 2010.
369 #define rcu_dereference_index_check(p, c) \
370 __rcu_dereference_index_check((p), (c))
373 * rcu_dereference_protected() - fetch RCU pointer when updates prevented
374 * @p: The pointer to read, prior to dereferencing
375 * @c: The conditions under which the dereference will take place
377 * Return the value of the specified RCU-protected pointer, but omit
378 * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This
379 * is useful in cases where update-side locks prevent the value of the
380 * pointer from changing. Please note that this primitive does -not-
381 * prevent the compiler from repeating this reference or combining it
382 * with other references, so it should not be used without protection
383 * of appropriate locks.
385 * This function is only for update-side use. Using this function
386 * when protected only by rcu_read_lock() will result in infrequent
387 * but very ugly failures.
389 #define rcu_dereference_protected(p, c) \
390 __rcu_dereference_protected((p), (c), __rcu)
393 * rcu_dereference_bh_protected() - fetch RCU-bh pointer when updates prevented
394 * @p: The pointer to read, prior to dereferencing
395 * @c: The conditions under which the dereference will take place
397 * This is the RCU-bh counterpart to rcu_dereference_protected().
399 #define rcu_dereference_bh_protected(p, c) \
400 __rcu_dereference_protected((p), (c), __rcu)
403 * rcu_dereference_sched_protected() - fetch RCU-sched pointer when updates prevented
404 * @p: The pointer to read, prior to dereferencing
405 * @c: The conditions under which the dereference will take place
407 * This is the RCU-sched counterpart to rcu_dereference_protected().
409 #define rcu_dereference_sched_protected(p, c) \
410 __rcu_dereference_protected((p), (c), __rcu)
414 * rcu_dereference() - fetch RCU-protected pointer for dereferencing
415 * @p: The pointer to read, prior to dereferencing
417 * This is a simple wrapper around rcu_dereference_check().
419 #define rcu_dereference(p) rcu_dereference_check(p, 0)
422 * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
423 * @p: The pointer to read, prior to dereferencing
425 * Makes rcu_dereference_check() do the dirty work.
427 #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
430 * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
431 * @p: The pointer to read, prior to dereferencing
433 * Makes rcu_dereference_check() do the dirty work.
435 #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
438 * rcu_read_lock() - mark the beginning of an RCU read-side critical section
440 * When synchronize_rcu() is invoked on one CPU while other CPUs
441 * are within RCU read-side critical sections, then the
442 * synchronize_rcu() is guaranteed to block until after all the other
443 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
444 * on one CPU while other CPUs are within RCU read-side critical
445 * sections, invocation of the corresponding RCU callback is deferred
446 * until after the all the other CPUs exit their critical sections.
448 * Note, however, that RCU callbacks are permitted to run concurrently
449 * with RCU read-side critical sections. One way that this can happen
450 * is via the following sequence of events: (1) CPU 0 enters an RCU
451 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
452 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
453 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
454 * callback is invoked. This is legal, because the RCU read-side critical
455 * section that was running concurrently with the call_rcu() (and which
456 * therefore might be referencing something that the corresponding RCU
457 * callback would free up) has completed before the corresponding
458 * RCU callback is invoked.
460 * RCU read-side critical sections may be nested. Any deferred actions
461 * will be deferred until the outermost RCU read-side critical section
464 * It is illegal to block while in an RCU read-side critical section.
466 static inline void rcu_read_lock(void)
474 * So where is rcu_write_lock()? It does not exist, as there is no
475 * way for writers to lock out RCU readers. This is a feature, not
476 * a bug -- this property is what provides RCU's performance benefits.
477 * Of course, writers must coordinate with each other. The normal
478 * spinlock primitives work well for this, but any other technique may be
479 * used as well. RCU does not care how the writers keep out of each
480 * others' way, as long as they do so.
484 * rcu_read_unlock() - marks the end of an RCU read-side critical section.
486 * See rcu_read_lock() for more information.
488 static inline void rcu_read_unlock(void)
496 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
498 * This is equivalent of rcu_read_lock(), but to be used when updates
499 * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since
500 * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a
501 * softirq handler to be a quiescent state, a process in RCU read-side
502 * critical section must be protected by disabling softirqs. Read-side
503 * critical sections in interrupt context can use just rcu_read_lock(),
504 * though this should at least be commented to avoid confusing people
507 static inline void rcu_read_lock_bh(void)
509 __rcu_read_lock_bh();
511 rcu_read_acquire_bh();
515 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
517 * See rcu_read_lock_bh() for more information.
519 static inline void rcu_read_unlock_bh(void)
521 rcu_read_release_bh();
523 __rcu_read_unlock_bh();
527 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
529 * This is equivalent of rcu_read_lock(), but to be used when updates
530 * are being done using call_rcu_sched() or synchronize_rcu_sched().
531 * Read-side critical sections can also be introduced by anything that
532 * disables preemption, including local_irq_disable() and friends.
534 static inline void rcu_read_lock_sched(void)
537 __acquire(RCU_SCHED);
538 rcu_read_acquire_sched();
541 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
542 static inline notrace void rcu_read_lock_sched_notrace(void)
544 preempt_disable_notrace();
545 __acquire(RCU_SCHED);
549 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
551 * See rcu_read_lock_sched for more information.
553 static inline void rcu_read_unlock_sched(void)
555 rcu_read_release_sched();
556 __release(RCU_SCHED);
560 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
561 static inline notrace void rcu_read_unlock_sched_notrace(void)
563 __release(RCU_SCHED);
564 preempt_enable_notrace();
568 * rcu_assign_pointer() - assign to RCU-protected pointer
569 * @p: pointer to assign to
570 * @v: value to assign (publish)
572 * Assigns the specified value to the specified RCU-protected
573 * pointer, ensuring that any concurrent RCU readers will see
574 * any prior initialization. Returns the value assigned.
576 * Inserts memory barriers on architectures that require them
577 * (pretty much all of them other than x86), and also prevents
578 * the compiler from reordering the code that initializes the
579 * structure after the pointer assignment. More importantly, this
580 * call documents which pointers will be dereferenced by RCU read-side
583 #define rcu_assign_pointer(p, v) \
584 __rcu_assign_pointer((p), (v), __rcu)
587 * RCU_INIT_POINTER() - initialize an RCU protected pointer
589 * Initialize an RCU-protected pointer in such a way to avoid RCU-lockdep
592 #define RCU_INIT_POINTER(p, v) \
593 p = (typeof(*v) __force __rcu *)(v)
595 /* Infrastructure to implement the synchronize_() primitives. */
597 struct rcu_synchronize {
598 struct rcu_head head;
599 struct completion completion;
602 extern void wakeme_after_rcu(struct rcu_head *head);
605 * call_rcu() - Queue an RCU callback for invocation after a grace period.
606 * @head: structure to be used for queueing the RCU updates.
607 * @func: actual update function to be invoked after the grace period
609 * The update function will be invoked some time after a full grace
610 * period elapses, in other words after all currently executing RCU
611 * read-side critical sections have completed. RCU read-side critical
612 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
615 extern void call_rcu(struct rcu_head *head,
616 void (*func)(struct rcu_head *head));
619 * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
620 * @head: structure to be used for queueing the RCU updates.
621 * @func: actual update function to be invoked after the grace period
623 * The update function will be invoked some time after a full grace
624 * period elapses, in other words after all currently executing RCU
625 * read-side critical sections have completed. call_rcu_bh() assumes
626 * that the read-side critical sections end on completion of a softirq
627 * handler. This means that read-side critical sections in process
628 * context must not be interrupted by softirqs. This interface is to be
629 * used when most of the read-side critical sections are in softirq context.
630 * RCU read-side critical sections are delimited by :
631 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
633 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
634 * These may be nested.
636 extern void call_rcu_bh(struct rcu_head *head,
637 void (*func)(struct rcu_head *head));
640 * debug_rcu_head_queue()/debug_rcu_head_unqueue() are used internally
641 * by call_rcu() and rcu callback execution, and are therefore not part of the
642 * RCU API. Leaving in rcupdate.h because they are used by all RCU flavors.
645 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
646 # define STATE_RCU_HEAD_READY 0
647 # define STATE_RCU_HEAD_QUEUED 1
649 extern struct debug_obj_descr rcuhead_debug_descr;
651 static inline void debug_rcu_head_queue(struct rcu_head *head)
653 debug_object_activate(head, &rcuhead_debug_descr);
654 debug_object_active_state(head, &rcuhead_debug_descr,
655 STATE_RCU_HEAD_READY,
656 STATE_RCU_HEAD_QUEUED);
659 static inline void debug_rcu_head_unqueue(struct rcu_head *head)
661 debug_object_active_state(head, &rcuhead_debug_descr,
662 STATE_RCU_HEAD_QUEUED,
663 STATE_RCU_HEAD_READY);
664 debug_object_deactivate(head, &rcuhead_debug_descr);
666 #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
667 static inline void debug_rcu_head_queue(struct rcu_head *head)
671 static inline void debug_rcu_head_unqueue(struct rcu_head *head)
674 #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
676 #endif /* __LINUX_RCUPDATE_H */