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/types.h>
37 #include <linux/cache.h>
38 #include <linux/spinlock.h>
39 #include <linux/threads.h>
40 #include <linux/cpumask.h>
41 #include <linux/seqlock.h>
42 #include <linux/lockdep.h>
43 #include <linux/completion.h>
44 #include <linux/debugobjects.h>
45 #include <linux/compiler.h>
47 #ifdef CONFIG_RCU_TORTURE_TEST
48 extern int rcutorture_runnable; /* for sysctl */
49 #endif /* #ifdef CONFIG_RCU_TORTURE_TEST */
51 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
52 extern void rcutorture_record_test_transition(void);
53 extern void rcutorture_record_progress(unsigned long vernum);
55 static inline void rcutorture_record_test_transition(void)
58 static inline void rcutorture_record_progress(unsigned long vernum)
63 #define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b))
64 #define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b))
65 #define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))
66 #define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b))
68 /* Exported common interfaces */
70 #ifdef CONFIG_PREEMPT_RCU
73 * call_rcu() - Queue an RCU callback for invocation after a grace period.
74 * @head: structure to be used for queueing the RCU updates.
75 * @func: actual callback function to be invoked after the grace period
77 * The callback function will be invoked some time after a full grace
78 * period elapses, in other words after all pre-existing RCU read-side
79 * critical sections have completed. However, the callback function
80 * might well execute concurrently with RCU read-side critical sections
81 * that started after call_rcu() was invoked. RCU read-side critical
82 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
85 extern void call_rcu(struct rcu_head *head,
86 void (*func)(struct rcu_head *head));
88 #else /* #ifdef CONFIG_PREEMPT_RCU */
90 /* In classic RCU, call_rcu() is just call_rcu_sched(). */
91 #define call_rcu call_rcu_sched
93 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
96 * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
97 * @head: structure to be used for queueing the RCU updates.
98 * @func: actual callback function to be invoked after the grace period
100 * The callback function will be invoked some time after a full grace
101 * period elapses, in other words after all currently executing RCU
102 * read-side critical sections have completed. call_rcu_bh() assumes
103 * that the read-side critical sections end on completion of a softirq
104 * handler. This means that read-side critical sections in process
105 * context must not be interrupted by softirqs. This interface is to be
106 * used when most of the read-side critical sections are in softirq context.
107 * RCU read-side critical sections are delimited by :
108 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
110 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
111 * These may be nested.
113 extern void call_rcu_bh(struct rcu_head *head,
114 void (*func)(struct rcu_head *head));
117 * call_rcu_sched() - Queue an RCU for invocation after sched grace period.
118 * @head: structure to be used for queueing the RCU updates.
119 * @func: actual callback function to be invoked after the grace period
121 * The callback function will be invoked some time after a full grace
122 * period elapses, in other words after all currently executing RCU
123 * read-side critical sections have completed. call_rcu_sched() assumes
124 * that the read-side critical sections end on enabling of preemption
125 * or on voluntary preemption.
126 * RCU read-side critical sections are delimited by :
127 * - rcu_read_lock_sched() and rcu_read_unlock_sched(),
129 * anything that disables preemption.
130 * These may be nested.
132 extern void call_rcu_sched(struct rcu_head *head,
133 void (*func)(struct rcu_head *rcu));
135 extern void synchronize_sched(void);
137 #ifdef CONFIG_PREEMPT_RCU
139 extern void __rcu_read_lock(void);
140 extern void __rcu_read_unlock(void);
141 void synchronize_rcu(void);
144 * Defined as a macro as it is a very low level header included from
145 * areas that don't even know about current. This gives the rcu_read_lock()
146 * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
147 * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
149 #define rcu_preempt_depth() (current->rcu_read_lock_nesting)
151 #else /* #ifdef CONFIG_PREEMPT_RCU */
153 static inline void __rcu_read_lock(void)
158 static inline void __rcu_read_unlock(void)
163 static inline void synchronize_rcu(void)
168 static inline int rcu_preempt_depth(void)
173 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
175 /* Internal to kernel */
176 extern void rcu_sched_qs(int cpu);
177 extern void rcu_bh_qs(int cpu);
178 extern void rcu_check_callbacks(int cpu, int user);
179 struct notifier_block;
183 extern void rcu_enter_nohz(void);
184 extern void rcu_exit_nohz(void);
186 #else /* #ifdef CONFIG_NO_HZ */
188 static inline void rcu_enter_nohz(void)
192 static inline void rcu_exit_nohz(void)
196 #endif /* #else #ifdef CONFIG_NO_HZ */
199 * Infrastructure to implement the synchronize_() primitives in
200 * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
203 typedef void call_rcu_func_t(struct rcu_head *head,
204 void (*func)(struct rcu_head *head));
205 void wait_rcu_gp(call_rcu_func_t crf);
207 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
208 #include <linux/rcutree.h>
209 #elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU)
210 #include <linux/rcutiny.h>
212 #error "Unknown RCU implementation specified to kernel configuration"
216 * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic
217 * initialization and destruction of rcu_head on the stack. rcu_head structures
218 * allocated dynamically in the heap or defined statically don't need any
221 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
222 extern void init_rcu_head_on_stack(struct rcu_head *head);
223 extern void destroy_rcu_head_on_stack(struct rcu_head *head);
224 #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
225 static inline void init_rcu_head_on_stack(struct rcu_head *head)
229 static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
232 #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
235 #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_NO_HZ)
236 extern bool rcu_check_extended_qs(void);
238 static inline bool rcu_check_extended_qs(void) { return false; }
242 #ifdef CONFIG_DEBUG_LOCK_ALLOC
244 #define PROVE_RCU(a) a
246 static inline void rcu_lock_acquire(struct lockdep_map *map)
248 WARN_ON_ONCE(rcu_check_extended_qs());
249 lock_acquire(map, 0, 0, 2, 1, NULL, _THIS_IP_);
252 static inline void rcu_lock_release(struct lockdep_map *map)
254 WARN_ON_ONCE(rcu_check_extended_qs());
255 lock_release(map, 1, _THIS_IP_);
258 extern struct lockdep_map rcu_lock_map;
259 extern struct lockdep_map rcu_bh_lock_map;
260 extern struct lockdep_map rcu_sched_lock_map;
261 extern int debug_lockdep_rcu_enabled(void);
264 * rcu_read_lock_held() - might we be in RCU read-side critical section?
266 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
267 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
268 * this assumes we are in an RCU read-side critical section unless it can
269 * prove otherwise. This is useful for debug checks in functions that
270 * require that they be called within an RCU read-side critical section.
272 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
273 * and while lockdep is disabled.
275 * Note that if the CPU is in an extended quiescent state, for example,
276 * if the CPU is in dyntick-idle mode, then rcu_read_lock_held() returns
277 * false even if the CPU did an rcu_read_lock(). The reason for this is
278 * that RCU ignores CPUs that are in extended quiescent states, so such
279 * a CPU is effectively never in an RCU read-side critical section
280 * regardless of what RCU primitives it invokes. This state of affairs
281 * is required -- RCU would otherwise need to periodically wake up
282 * dyntick-idle CPUs, which would defeat the whole purpose of dyntick-idle
285 static inline int rcu_read_lock_held(void)
287 if (!debug_lockdep_rcu_enabled())
290 if (rcu_check_extended_qs())
293 return lock_is_held(&rcu_lock_map);
297 * rcu_read_lock_bh_held() is defined out of line to avoid #include-file
300 extern int rcu_read_lock_bh_held(void);
303 * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
305 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
306 * RCU-sched read-side critical section. In absence of
307 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
308 * critical section unless it can prove otherwise. Note that disabling
309 * of preemption (including disabling irqs) counts as an RCU-sched
310 * read-side critical section. This is useful for debug checks in functions
311 * that required that they be called within an RCU-sched read-side
314 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
315 * and while lockdep is disabled.
317 * Note that if the CPU is in an extended quiescent state, for example,
318 * if the CPU is in dyntick-idle mode, then rcu_read_lock_held() returns
319 * false even if the CPU did an rcu_read_lock(). The reason for this is
320 * that RCU ignores CPUs that are in extended quiescent states, so such
321 * a CPU is effectively never in an RCU read-side critical section
322 * regardless of what RCU primitives it invokes. This state of affairs
323 * is required -- RCU would otherwise need to periodically wake up
324 * dyntick-idle CPUs, which would defeat the whole purpose of dyntick-idle
327 #ifdef CONFIG_PREEMPT
328 static inline int rcu_read_lock_sched_held(void)
330 int lockdep_opinion = 0;
332 if (!debug_lockdep_rcu_enabled())
335 if (rcu_check_extended_qs())
339 lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
340 return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
342 #else /* #ifdef CONFIG_PREEMPT */
343 static inline int rcu_read_lock_sched_held(void)
347 #endif /* #else #ifdef CONFIG_PREEMPT */
349 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
351 # define PROVE_RCU(a) do { } while (0)
352 # define rcu_lock_acquire(a) do { } while (0)
353 # define rcu_lock_release(a) do { } while (0)
355 static inline int rcu_read_lock_held(void)
360 static inline int rcu_read_lock_bh_held(void)
365 #ifdef CONFIG_PREEMPT
366 static inline int rcu_read_lock_sched_held(void)
368 return preempt_count() != 0 || irqs_disabled();
370 #else /* #ifdef CONFIG_PREEMPT */
371 static inline int rcu_read_lock_sched_held(void)
375 #endif /* #else #ifdef CONFIG_PREEMPT */
377 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
379 #ifdef CONFIG_PROVE_RCU
381 extern int rcu_my_thread_group_empty(void);
384 * rcu_lockdep_assert - emit lockdep splat if specified condition not met
385 * @c: condition to check
386 * @s: informative message
388 #define rcu_lockdep_assert(c, s) \
390 static bool __warned; \
391 if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
393 lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
397 #define rcu_sleep_check() \
399 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map), \
400 "Illegal context switch in RCU-bh" \
401 " read-side critical section"); \
402 rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map), \
403 "Illegal context switch in RCU-sched"\
404 " read-side critical section"); \
407 #else /* #ifdef CONFIG_PROVE_RCU */
409 #define rcu_lockdep_assert(c, s) do { } while (0)
410 #define rcu_sleep_check() do { } while (0)
412 #endif /* #else #ifdef CONFIG_PROVE_RCU */
415 * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
416 * and rcu_assign_pointer(). Some of these could be folded into their
417 * callers, but they are left separate in order to ease introduction of
418 * multiple flavors of pointers to match the multiple flavors of RCU
419 * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in
424 #define rcu_dereference_sparse(p, space) \
425 ((void)(((typeof(*p) space *)p) == p))
426 #else /* #ifdef __CHECKER__ */
427 #define rcu_dereference_sparse(p, space)
428 #endif /* #else #ifdef __CHECKER__ */
430 #define __rcu_access_pointer(p, space) \
432 typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
433 rcu_dereference_sparse(p, space); \
434 ((typeof(*p) __force __kernel *)(_________p1)); \
436 #define __rcu_dereference_check(p, c, space) \
438 typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
439 rcu_lockdep_assert(c, "suspicious rcu_dereference_check()" \
441 rcu_dereference_sparse(p, space); \
442 smp_read_barrier_depends(); \
443 ((typeof(*p) __force __kernel *)(_________p1)); \
445 #define __rcu_dereference_protected(p, c, space) \
447 rcu_lockdep_assert(c, "suspicious rcu_dereference_protected()" \
449 rcu_dereference_sparse(p, space); \
450 ((typeof(*p) __force __kernel *)(p)); \
453 #define __rcu_access_index(p, space) \
455 typeof(p) _________p1 = ACCESS_ONCE(p); \
456 rcu_dereference_sparse(p, space); \
459 #define __rcu_dereference_index_check(p, c) \
461 typeof(p) _________p1 = ACCESS_ONCE(p); \
462 rcu_lockdep_assert(c, \
463 "suspicious rcu_dereference_index_check()" \
465 smp_read_barrier_depends(); \
468 #define __rcu_assign_pointer(p, v, space) \
471 (p) = (typeof(*v) __force space *)(v); \
476 * rcu_access_pointer() - fetch RCU pointer with no dereferencing
477 * @p: The pointer to read
479 * Return the value of the specified RCU-protected pointer, but omit the
480 * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful
481 * when the value of this pointer is accessed, but the pointer is not
482 * dereferenced, for example, when testing an RCU-protected pointer against
483 * NULL. Although rcu_access_pointer() may also be used in cases where
484 * update-side locks prevent the value of the pointer from changing, you
485 * should instead use rcu_dereference_protected() for this use case.
487 #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
490 * rcu_dereference_check() - rcu_dereference with debug checking
491 * @p: The pointer to read, prior to dereferencing
492 * @c: The conditions under which the dereference will take place
494 * Do an rcu_dereference(), but check that the conditions under which the
495 * dereference will take place are correct. Typically the conditions
496 * indicate the various locking conditions that should be held at that
497 * point. The check should return true if the conditions are satisfied.
498 * An implicit check for being in an RCU read-side critical section
499 * (rcu_read_lock()) is included.
503 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
505 * could be used to indicate to lockdep that foo->bar may only be dereferenced
506 * if either rcu_read_lock() is held, or that the lock required to replace
507 * the bar struct at foo->bar is held.
509 * Note that the list of conditions may also include indications of when a lock
510 * need not be held, for example during initialisation or destruction of the
513 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
514 * atomic_read(&foo->usage) == 0);
516 * Inserts memory barriers on architectures that require them
517 * (currently only the Alpha), prevents the compiler from refetching
518 * (and from merging fetches), and, more importantly, documents exactly
519 * which pointers are protected by RCU and checks that the pointer is
520 * annotated as __rcu.
522 #define rcu_dereference_check(p, c) \
523 __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)
526 * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
527 * @p: The pointer to read, prior to dereferencing
528 * @c: The conditions under which the dereference will take place
530 * This is the RCU-bh counterpart to rcu_dereference_check().
532 #define rcu_dereference_bh_check(p, c) \
533 __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu)
536 * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
537 * @p: The pointer to read, prior to dereferencing
538 * @c: The conditions under which the dereference will take place
540 * This is the RCU-sched counterpart to rcu_dereference_check().
542 #define rcu_dereference_sched_check(p, c) \
543 __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \
546 #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/
549 * rcu_access_index() - fetch RCU index with no dereferencing
550 * @p: The index to read
552 * Return the value of the specified RCU-protected index, but omit the
553 * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful
554 * when the value of this index is accessed, but the index is not
555 * dereferenced, for example, when testing an RCU-protected index against
556 * -1. Although rcu_access_index() may also be used in cases where
557 * update-side locks prevent the value of the index from changing, you
558 * should instead use rcu_dereference_index_protected() for this use case.
560 #define rcu_access_index(p) __rcu_access_index((p), __rcu)
563 * rcu_dereference_index_check() - rcu_dereference for indices with debug checking
564 * @p: The pointer to read, prior to dereferencing
565 * @c: The conditions under which the dereference will take place
567 * Similar to rcu_dereference_check(), but omits the sparse checking.
568 * This allows rcu_dereference_index_check() to be used on integers,
569 * which can then be used as array indices. Attempting to use
570 * rcu_dereference_check() on an integer will give compiler warnings
571 * because the sparse address-space mechanism relies on dereferencing
572 * the RCU-protected pointer. Dereferencing integers is not something
573 * that even gcc will put up with.
575 * Note that this function does not implicitly check for RCU read-side
576 * critical sections. If this function gains lots of uses, it might
577 * make sense to provide versions for each flavor of RCU, but it does
578 * not make sense as of early 2010.
580 #define rcu_dereference_index_check(p, c) \
581 __rcu_dereference_index_check((p), (c))
584 * rcu_dereference_protected() - fetch RCU pointer when updates prevented
585 * @p: The pointer to read, prior to dereferencing
586 * @c: The conditions under which the dereference will take place
588 * Return the value of the specified RCU-protected pointer, but omit
589 * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This
590 * is useful in cases where update-side locks prevent the value of the
591 * pointer from changing. Please note that this primitive does -not-
592 * prevent the compiler from repeating this reference or combining it
593 * with other references, so it should not be used without protection
594 * of appropriate locks.
596 * This function is only for update-side use. Using this function
597 * when protected only by rcu_read_lock() will result in infrequent
598 * but very ugly failures.
600 #define rcu_dereference_protected(p, c) \
601 __rcu_dereference_protected((p), (c), __rcu)
605 * rcu_dereference() - fetch RCU-protected pointer for dereferencing
606 * @p: The pointer to read, prior to dereferencing
608 * This is a simple wrapper around rcu_dereference_check().
610 #define rcu_dereference(p) rcu_dereference_check(p, 0)
613 * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
614 * @p: The pointer to read, prior to dereferencing
616 * Makes rcu_dereference_check() do the dirty work.
618 #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
621 * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
622 * @p: The pointer to read, prior to dereferencing
624 * Makes rcu_dereference_check() do the dirty work.
626 #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
629 * rcu_read_lock() - mark the beginning of an RCU read-side critical section
631 * When synchronize_rcu() is invoked on one CPU while other CPUs
632 * are within RCU read-side critical sections, then the
633 * synchronize_rcu() is guaranteed to block until after all the other
634 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
635 * on one CPU while other CPUs are within RCU read-side critical
636 * sections, invocation of the corresponding RCU callback is deferred
637 * until after the all the other CPUs exit their critical sections.
639 * Note, however, that RCU callbacks are permitted to run concurrently
640 * with new RCU read-side critical sections. One way that this can happen
641 * is via the following sequence of events: (1) CPU 0 enters an RCU
642 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
643 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
644 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
645 * callback is invoked. This is legal, because the RCU read-side critical
646 * section that was running concurrently with the call_rcu() (and which
647 * therefore might be referencing something that the corresponding RCU
648 * callback would free up) has completed before the corresponding
649 * RCU callback is invoked.
651 * RCU read-side critical sections may be nested. Any deferred actions
652 * will be deferred until the outermost RCU read-side critical section
655 * You can avoid reading and understanding the next paragraph by
656 * following this rule: don't put anything in an rcu_read_lock() RCU
657 * read-side critical section that would block in a !PREEMPT kernel.
658 * But if you want the full story, read on!
660 * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it
661 * is illegal to block while in an RCU read-side critical section. In
662 * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU)
663 * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may
664 * be preempted, but explicit blocking is illegal. Finally, in preemptible
665 * RCU implementations in real-time (CONFIG_PREEMPT_RT) kernel builds,
666 * RCU read-side critical sections may be preempted and they may also
667 * block, but only when acquiring spinlocks that are subject to priority
670 static inline void rcu_read_lock(void)
674 rcu_lock_acquire(&rcu_lock_map);
678 * So where is rcu_write_lock()? It does not exist, as there is no
679 * way for writers to lock out RCU readers. This is a feature, not
680 * a bug -- this property is what provides RCU's performance benefits.
681 * Of course, writers must coordinate with each other. The normal
682 * spinlock primitives work well for this, but any other technique may be
683 * used as well. RCU does not care how the writers keep out of each
684 * others' way, as long as they do so.
688 * rcu_read_unlock() - marks the end of an RCU read-side critical section.
690 * See rcu_read_lock() for more information.
692 static inline void rcu_read_unlock(void)
694 rcu_lock_release(&rcu_lock_map);
700 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
702 * This is equivalent of rcu_read_lock(), but to be used when updates
703 * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since
704 * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a
705 * softirq handler to be a quiescent state, a process in RCU read-side
706 * critical section must be protected by disabling softirqs. Read-side
707 * critical sections in interrupt context can use just rcu_read_lock(),
708 * though this should at least be commented to avoid confusing people
711 static inline void rcu_read_lock_bh(void)
715 rcu_lock_acquire(&rcu_bh_lock_map);
719 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
721 * See rcu_read_lock_bh() for more information.
723 static inline void rcu_read_unlock_bh(void)
725 rcu_lock_release(&rcu_bh_lock_map);
731 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
733 * This is equivalent of rcu_read_lock(), but to be used when updates
734 * are being done using call_rcu_sched() or synchronize_rcu_sched().
735 * Read-side critical sections can also be introduced by anything that
736 * disables preemption, including local_irq_disable() and friends.
738 static inline void rcu_read_lock_sched(void)
741 __acquire(RCU_SCHED);
742 rcu_lock_acquire(&rcu_sched_lock_map);
745 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
746 static inline notrace void rcu_read_lock_sched_notrace(void)
748 preempt_disable_notrace();
749 __acquire(RCU_SCHED);
753 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
755 * See rcu_read_lock_sched for more information.
757 static inline void rcu_read_unlock_sched(void)
759 rcu_lock_release(&rcu_sched_lock_map);
760 __release(RCU_SCHED);
764 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
765 static inline notrace void rcu_read_unlock_sched_notrace(void)
767 __release(RCU_SCHED);
768 preempt_enable_notrace();
772 * rcu_assign_pointer() - assign to RCU-protected pointer
773 * @p: pointer to assign to
774 * @v: value to assign (publish)
776 * Assigns the specified value to the specified RCU-protected
777 * pointer, ensuring that any concurrent RCU readers will see
778 * any prior initialization. Returns the value assigned.
780 * Inserts memory barriers on architectures that require them
781 * (which is most of them), and also prevents the compiler from
782 * reordering the code that initializes the structure after the pointer
783 * assignment. More importantly, this call documents which pointers
784 * will be dereferenced by RCU read-side code.
786 * In some special cases, you may use RCU_INIT_POINTER() instead
787 * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due
788 * to the fact that it does not constrain either the CPU or the compiler.
789 * That said, using RCU_INIT_POINTER() when you should have used
790 * rcu_assign_pointer() is a very bad thing that results in
791 * impossible-to-diagnose memory corruption. So please be careful.
792 * See the RCU_INIT_POINTER() comment header for details.
794 #define rcu_assign_pointer(p, v) \
795 __rcu_assign_pointer((p), (v), __rcu)
798 * RCU_INIT_POINTER() - initialize an RCU protected pointer
800 * Initialize an RCU-protected pointer in special cases where readers
801 * do not need ordering constraints on the CPU or the compiler. These
804 * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer -or-
805 * 2. The caller has taken whatever steps are required to prevent
806 * RCU readers from concurrently accessing this pointer -or-
807 * 3. The referenced data structure has already been exposed to
808 * readers either at compile time or via rcu_assign_pointer() -and-
809 * a. You have not made -any- reader-visible changes to
810 * this structure since then -or-
811 * b. It is OK for readers accessing this structure from its
812 * new location to see the old state of the structure. (For
813 * example, the changes were to statistical counters or to
814 * other state where exact synchronization is not required.)
816 * Failure to follow these rules governing use of RCU_INIT_POINTER() will
817 * result in impossible-to-diagnose memory corruption. As in the structures
818 * will look OK in crash dumps, but any concurrent RCU readers might
819 * see pre-initialized values of the referenced data structure. So
820 * please be very careful how you use RCU_INIT_POINTER()!!!
822 * If you are creating an RCU-protected linked structure that is accessed
823 * by a single external-to-structure RCU-protected pointer, then you may
824 * use RCU_INIT_POINTER() to initialize the internal RCU-protected
825 * pointers, but you must use rcu_assign_pointer() to initialize the
826 * external-to-structure pointer -after- you have completely initialized
827 * the reader-accessible portions of the linked structure.
829 #define RCU_INIT_POINTER(p, v) \
830 p = (typeof(*v) __force __rcu *)(v)
832 static __always_inline bool __is_kfree_rcu_offset(unsigned long offset)
834 return offset < 4096;
837 static __always_inline
838 void __kfree_rcu(struct rcu_head *head, unsigned long offset)
840 typedef void (*rcu_callback)(struct rcu_head *);
842 BUILD_BUG_ON(!__builtin_constant_p(offset));
844 /* See the kfree_rcu() header comment. */
845 BUILD_BUG_ON(!__is_kfree_rcu_offset(offset));
847 call_rcu(head, (rcu_callback)offset);
851 * kfree_rcu() - kfree an object after a grace period.
852 * @ptr: pointer to kfree
853 * @rcu_head: the name of the struct rcu_head within the type of @ptr.
855 * Many rcu callbacks functions just call kfree() on the base structure.
856 * These functions are trivial, but their size adds up, and furthermore
857 * when they are used in a kernel module, that module must invoke the
858 * high-latency rcu_barrier() function at module-unload time.
860 * The kfree_rcu() function handles this issue. Rather than encoding a
861 * function address in the embedded rcu_head structure, kfree_rcu() instead
862 * encodes the offset of the rcu_head structure within the base structure.
863 * Because the functions are not allowed in the low-order 4096 bytes of
864 * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
865 * If the offset is larger than 4095 bytes, a compile-time error will
866 * be generated in __kfree_rcu(). If this error is triggered, you can
867 * either fall back to use of call_rcu() or rearrange the structure to
868 * position the rcu_head structure into the first 4096 bytes.
870 * Note that the allowable offset might decrease in the future, for example,
871 * to allow something like kmem_cache_free_rcu().
873 #define kfree_rcu(ptr, rcu_head) \
874 __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
876 #endif /* __LINUX_RCUPDATE_H */