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 static inline void __rcu_read_lock_bh(void)
142 static inline void __rcu_read_unlock_bh(void)
147 #ifdef CONFIG_PREEMPT_RCU
149 extern void __rcu_read_lock(void);
150 extern void __rcu_read_unlock(void);
151 void synchronize_rcu(void);
154 * Defined as a macro as it is a very low level header included from
155 * areas that don't even know about current. This gives the rcu_read_lock()
156 * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
157 * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
159 #define rcu_preempt_depth() (current->rcu_read_lock_nesting)
161 #else /* #ifdef CONFIG_PREEMPT_RCU */
163 static inline void __rcu_read_lock(void)
168 static inline void __rcu_read_unlock(void)
173 static inline void synchronize_rcu(void)
178 static inline int rcu_preempt_depth(void)
183 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
185 /* Internal to kernel */
186 extern void rcu_sched_qs(int cpu
);
187 extern void rcu_bh_qs(int cpu
);
188 extern void rcu_check_callbacks(int cpu
, int user
);
189 struct notifier_block
;
193 extern void rcu_enter_nohz(void);
194 extern void rcu_exit_nohz(void);
196 #else /* #ifdef CONFIG_NO_HZ */
198 static inline void rcu_enter_nohz(void)
202 static inline void rcu_exit_nohz(void)
206 #endif /* #else #ifdef CONFIG_NO_HZ */
209 * Infrastructure to implement the synchronize_() primitives in
210 * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
213 typedef void call_rcu_func_t(struct rcu_head
*head
,
214 void (*func
)(struct rcu_head
*head
));
215 void wait_rcu_gp(call_rcu_func_t crf
);
217 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
218 #include <linux/rcutree.h>
219 #elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU)
220 #include <linux/rcutiny.h>
222 #error "Unknown RCU implementation specified to kernel configuration"
226 * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic
227 * initialization and destruction of rcu_head on the stack. rcu_head structures
228 * allocated dynamically in the heap or defined statically don't need any
231 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
232 extern void init_rcu_head_on_stack(struct rcu_head
*head
);
233 extern void destroy_rcu_head_on_stack(struct rcu_head
*head
);
234 #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
235 static inline void init_rcu_head_on_stack(struct rcu_head
*head
)
239 static inline void destroy_rcu_head_on_stack(struct rcu_head
*head
)
242 #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
244 #ifdef CONFIG_DEBUG_LOCK_ALLOC
246 extern struct lockdep_map rcu_lock_map
;
247 # define rcu_read_acquire() \
248 lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
249 # define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_)
251 extern struct lockdep_map rcu_bh_lock_map
;
252 # define rcu_read_acquire_bh() \
253 lock_acquire(&rcu_bh_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
254 # define rcu_read_release_bh() lock_release(&rcu_bh_lock_map, 1, _THIS_IP_)
256 extern struct lockdep_map rcu_sched_lock_map
;
257 # define rcu_read_acquire_sched() \
258 lock_acquire(&rcu_sched_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
259 # define rcu_read_release_sched() \
260 lock_release(&rcu_sched_lock_map, 1, _THIS_IP_)
262 extern int debug_lockdep_rcu_enabled(void);
265 * rcu_read_lock_held() - might we be in RCU read-side critical section?
267 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
268 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
269 * this assumes we are in an RCU read-side critical section unless it can
270 * prove otherwise. This is useful for debug checks in functions that
271 * require that they be called within an RCU read-side critical section.
273 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
274 * and while lockdep is disabled.
276 static inline int rcu_read_lock_held(void)
278 if (!debug_lockdep_rcu_enabled())
280 return lock_is_held(&rcu_lock_map
);
284 * rcu_read_lock_bh_held() is defined out of line to avoid #include-file
287 extern int rcu_read_lock_bh_held(void);
290 * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
292 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
293 * RCU-sched read-side critical section. In absence of
294 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
295 * critical section unless it can prove otherwise. Note that disabling
296 * of preemption (including disabling irqs) counts as an RCU-sched
297 * read-side critical section. This is useful for debug checks in functions
298 * that required that they be called within an RCU-sched read-side
301 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
302 * and while lockdep is disabled.
304 #ifdef CONFIG_PREEMPT_COUNT
305 static inline int rcu_read_lock_sched_held(void)
307 int lockdep_opinion
= 0;
309 if (!debug_lockdep_rcu_enabled())
312 lockdep_opinion
= lock_is_held(&rcu_sched_lock_map
);
313 return lockdep_opinion
|| preempt_count() != 0 || irqs_disabled();
315 #else /* #ifdef CONFIG_PREEMPT_COUNT */
316 static inline int rcu_read_lock_sched_held(void)
320 #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
322 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
324 # define rcu_read_acquire() do { } while (0)
325 # define rcu_read_release() do { } while (0)
326 # define rcu_read_acquire_bh() do { } while (0)
327 # define rcu_read_release_bh() do { } while (0)
328 # define rcu_read_acquire_sched() do { } while (0)
329 # define rcu_read_release_sched() do { } while (0)
331 static inline int rcu_read_lock_held(void)
336 static inline int rcu_read_lock_bh_held(void)
341 #ifdef CONFIG_PREEMPT_COUNT
342 static inline int rcu_read_lock_sched_held(void)
344 return preempt_count() != 0 || irqs_disabled();
346 #else /* #ifdef CONFIG_PREEMPT_COUNT */
347 static inline int rcu_read_lock_sched_held(void)
351 #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
353 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
355 #ifdef CONFIG_PROVE_RCU
357 extern int rcu_my_thread_group_empty(void);
360 * rcu_lockdep_assert - emit lockdep splat if specified condition not met
361 * @c: condition to check
362 * @s: informative message
364 #define rcu_lockdep_assert(c, s) \
366 static bool __warned; \
367 if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
369 lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
373 #define rcu_sleep_check() \
375 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map), \
376 "Illegal context switch in RCU-bh" \
377 " read-side critical section"); \
378 rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map), \
379 "Illegal context switch in RCU-sched"\
380 " read-side critical section"); \
383 #else /* #ifdef CONFIG_PROVE_RCU */
385 #define rcu_lockdep_assert(c, s) do { } while (0)
386 #define rcu_sleep_check() do { } while (0)
388 #endif /* #else #ifdef CONFIG_PROVE_RCU */
391 * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
392 * and rcu_assign_pointer(). Some of these could be folded into their
393 * callers, but they are left separate in order to ease introduction of
394 * multiple flavors of pointers to match the multiple flavors of RCU
395 * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in
400 #define rcu_dereference_sparse(p, space) \
401 ((void)(((typeof(*p) space *)p) == p))
402 #else /* #ifdef __CHECKER__ */
403 #define rcu_dereference_sparse(p, space)
404 #endif /* #else #ifdef __CHECKER__ */
406 #define __rcu_access_pointer(p, space) \
408 typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
409 rcu_dereference_sparse(p, space); \
410 ((typeof(*p) __force __kernel *)(_________p1)); \
412 #define __rcu_dereference_check(p, c, space) \
414 typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
415 rcu_lockdep_assert(c, "suspicious rcu_dereference_check()" \
417 rcu_dereference_sparse(p, space); \
418 smp_read_barrier_depends(); \
419 ((typeof(*p) __force __kernel *)(_________p1)); \
421 #define __rcu_dereference_protected(p, c, space) \
423 rcu_lockdep_assert(c, "suspicious rcu_dereference_protected()" \
425 rcu_dereference_sparse(p, space); \
426 ((typeof(*p) __force __kernel *)(p)); \
429 #define __rcu_access_index(p, space) \
431 typeof(p) _________p1 = ACCESS_ONCE(p); \
432 rcu_dereference_sparse(p, space); \
435 #define __rcu_dereference_index_check(p, c) \
437 typeof(p) _________p1 = ACCESS_ONCE(p); \
438 rcu_lockdep_assert(c, \
439 "suspicious rcu_dereference_index_check()" \
441 smp_read_barrier_depends(); \
444 #define __rcu_assign_pointer(p, v, space) \
446 if (!__builtin_constant_p(v) || \
449 (p) = (typeof(*v) __force space *)(v); \
454 * rcu_access_pointer() - fetch RCU pointer with no dereferencing
455 * @p: The pointer to read
457 * Return the value of the specified RCU-protected pointer, but omit the
458 * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful
459 * when the value of this pointer is accessed, but the pointer is not
460 * dereferenced, for example, when testing an RCU-protected pointer against
461 * NULL. Although rcu_access_pointer() may also be used in cases where
462 * update-side locks prevent the value of the pointer from changing, you
463 * should instead use rcu_dereference_protected() for this use case.
465 #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
468 * rcu_dereference_check() - rcu_dereference with debug checking
469 * @p: The pointer to read, prior to dereferencing
470 * @c: The conditions under which the dereference will take place
472 * Do an rcu_dereference(), but check that the conditions under which the
473 * dereference will take place are correct. Typically the conditions
474 * indicate the various locking conditions that should be held at that
475 * point. The check should return true if the conditions are satisfied.
476 * An implicit check for being in an RCU read-side critical section
477 * (rcu_read_lock()) is included.
481 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
483 * could be used to indicate to lockdep that foo->bar may only be dereferenced
484 * if either rcu_read_lock() is held, or that the lock required to replace
485 * the bar struct at foo->bar is held.
487 * Note that the list of conditions may also include indications of when a lock
488 * need not be held, for example during initialisation or destruction of the
491 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
492 * atomic_read(&foo->usage) == 0);
494 * Inserts memory barriers on architectures that require them
495 * (currently only the Alpha), prevents the compiler from refetching
496 * (and from merging fetches), and, more importantly, documents exactly
497 * which pointers are protected by RCU and checks that the pointer is
498 * annotated as __rcu.
500 #define rcu_dereference_check(p, c) \
501 __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)
504 * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
505 * @p: The pointer to read, prior to dereferencing
506 * @c: The conditions under which the dereference will take place
508 * This is the RCU-bh counterpart to rcu_dereference_check().
510 #define rcu_dereference_bh_check(p, c) \
511 __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu)
514 * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
515 * @p: The pointer to read, prior to dereferencing
516 * @c: The conditions under which the dereference will take place
518 * This is the RCU-sched counterpart to rcu_dereference_check().
520 #define rcu_dereference_sched_check(p, c) \
521 __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \
524 #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/
527 * rcu_access_index() - fetch RCU index with no dereferencing
528 * @p: The index to read
530 * Return the value of the specified RCU-protected index, but omit the
531 * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful
532 * when the value of this index is accessed, but the index is not
533 * dereferenced, for example, when testing an RCU-protected index against
534 * -1. Although rcu_access_index() may also be used in cases where
535 * update-side locks prevent the value of the index from changing, you
536 * should instead use rcu_dereference_index_protected() for this use case.
538 #define rcu_access_index(p) __rcu_access_index((p), __rcu)
541 * rcu_dereference_index_check() - rcu_dereference for indices with debug checking
542 * @p: The pointer to read, prior to dereferencing
543 * @c: The conditions under which the dereference will take place
545 * Similar to rcu_dereference_check(), but omits the sparse checking.
546 * This allows rcu_dereference_index_check() to be used on integers,
547 * which can then be used as array indices. Attempting to use
548 * rcu_dereference_check() on an integer will give compiler warnings
549 * because the sparse address-space mechanism relies on dereferencing
550 * the RCU-protected pointer. Dereferencing integers is not something
551 * that even gcc will put up with.
553 * Note that this function does not implicitly check for RCU read-side
554 * critical sections. If this function gains lots of uses, it might
555 * make sense to provide versions for each flavor of RCU, but it does
556 * not make sense as of early 2010.
558 #define rcu_dereference_index_check(p, c) \
559 __rcu_dereference_index_check((p), (c))
562 * rcu_dereference_protected() - fetch RCU pointer when updates prevented
563 * @p: The pointer to read, prior to dereferencing
564 * @c: The conditions under which the dereference will take place
566 * Return the value of the specified RCU-protected pointer, but omit
567 * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This
568 * is useful in cases where update-side locks prevent the value of the
569 * pointer from changing. Please note that this primitive does -not-
570 * prevent the compiler from repeating this reference or combining it
571 * with other references, so it should not be used without protection
572 * of appropriate locks.
574 * This function is only for update-side use. Using this function
575 * when protected only by rcu_read_lock() will result in infrequent
576 * but very ugly failures.
578 #define rcu_dereference_protected(p, c) \
579 __rcu_dereference_protected((p), (c), __rcu)
582 * rcu_dereference_bh_protected() - fetch RCU-bh pointer when updates prevented
583 * @p: The pointer to read, prior to dereferencing
584 * @c: The conditions under which the dereference will take place
586 * This is the RCU-bh counterpart to rcu_dereference_protected().
588 #define rcu_dereference_bh_protected(p, c) \
589 __rcu_dereference_protected((p), (c), __rcu)
592 * rcu_dereference_sched_protected() - fetch RCU-sched pointer when updates prevented
593 * @p: The pointer to read, prior to dereferencing
594 * @c: The conditions under which the dereference will take place
596 * This is the RCU-sched counterpart to rcu_dereference_protected().
598 #define rcu_dereference_sched_protected(p, c) \
599 __rcu_dereference_protected((p), (c), __rcu)
603 * rcu_dereference() - fetch RCU-protected pointer for dereferencing
604 * @p: The pointer to read, prior to dereferencing
606 * This is a simple wrapper around rcu_dereference_check().
608 #define rcu_dereference(p) rcu_dereference_check(p, 0)
611 * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
612 * @p: The pointer to read, prior to dereferencing
614 * Makes rcu_dereference_check() do the dirty work.
616 #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
619 * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
620 * @p: The pointer to read, prior to dereferencing
622 * Makes rcu_dereference_check() do the dirty work.
624 #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
627 * rcu_read_lock() - mark the beginning of an RCU read-side critical section
629 * When synchronize_rcu() is invoked on one CPU while other CPUs
630 * are within RCU read-side critical sections, then the
631 * synchronize_rcu() is guaranteed to block until after all the other
632 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
633 * on one CPU while other CPUs are within RCU read-side critical
634 * sections, invocation of the corresponding RCU callback is deferred
635 * until after the all the other CPUs exit their critical sections.
637 * Note, however, that RCU callbacks are permitted to run concurrently
638 * with new RCU read-side critical sections. One way that this can happen
639 * is via the following sequence of events: (1) CPU 0 enters an RCU
640 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
641 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
642 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
643 * callback is invoked. This is legal, because the RCU read-side critical
644 * section that was running concurrently with the call_rcu() (and which
645 * therefore might be referencing something that the corresponding RCU
646 * callback would free up) has completed before the corresponding
647 * RCU callback is invoked.
649 * RCU read-side critical sections may be nested. Any deferred actions
650 * will be deferred until the outermost RCU read-side critical section
653 * You can avoid reading and understanding the next paragraph by
654 * following this rule: don't put anything in an rcu_read_lock() RCU
655 * read-side critical section that would block in a !PREEMPT kernel.
656 * But if you want the full story, read on!
658 * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it
659 * is illegal to block while in an RCU read-side critical section. In
660 * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU)
661 * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may
662 * be preempted, but explicit blocking is illegal. Finally, in preemptible
663 * RCU implementations in real-time (CONFIG_PREEMPT_RT) kernel builds,
664 * RCU read-side critical sections may be preempted and they may also
665 * block, but only when acquiring spinlocks that are subject to priority
668 static inline void rcu_read_lock(void)
676 * So where is rcu_write_lock()? It does not exist, as there is no
677 * way for writers to lock out RCU readers. This is a feature, not
678 * a bug -- this property is what provides RCU's performance benefits.
679 * Of course, writers must coordinate with each other. The normal
680 * spinlock primitives work well for this, but any other technique may be
681 * used as well. RCU does not care how the writers keep out of each
682 * others' way, as long as they do so.
686 * rcu_read_unlock() - marks the end of an RCU read-side critical section.
688 * See rcu_read_lock() for more information.
690 static inline void rcu_read_unlock(void)
698 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
700 * This is equivalent of rcu_read_lock(), but to be used when updates
701 * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since
702 * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a
703 * softirq handler to be a quiescent state, a process in RCU read-side
704 * critical section must be protected by disabling softirqs. Read-side
705 * critical sections in interrupt context can use just rcu_read_lock(),
706 * though this should at least be commented to avoid confusing people
709 static inline void rcu_read_lock_bh(void)
711 __rcu_read_lock_bh();
713 rcu_read_acquire_bh();
717 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
719 * See rcu_read_lock_bh() for more information.
721 static inline void rcu_read_unlock_bh(void)
723 rcu_read_release_bh();
725 __rcu_read_unlock_bh();
729 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
731 * This is equivalent of rcu_read_lock(), but to be used when updates
732 * are being done using call_rcu_sched() or synchronize_rcu_sched().
733 * Read-side critical sections can also be introduced by anything that
734 * disables preemption, including local_irq_disable() and friends.
736 static inline void rcu_read_lock_sched(void)
739 __acquire(RCU_SCHED
);
740 rcu_read_acquire_sched();
743 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
744 static inline notrace
void rcu_read_lock_sched_notrace(void)
746 preempt_disable_notrace();
747 __acquire(RCU_SCHED
);
751 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
753 * See rcu_read_lock_sched for more information.
755 static inline void rcu_read_unlock_sched(void)
757 rcu_read_release_sched();
758 __release(RCU_SCHED
);
762 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
763 static inline notrace
void rcu_read_unlock_sched_notrace(void)
765 __release(RCU_SCHED
);
766 preempt_enable_notrace();
770 * rcu_assign_pointer() - assign to RCU-protected pointer
771 * @p: pointer to assign to
772 * @v: value to assign (publish)
774 * Assigns the specified value to the specified RCU-protected
775 * pointer, ensuring that any concurrent RCU readers will see
776 * any prior initialization. Returns the value assigned.
778 * Inserts memory barriers on architectures that require them
779 * (pretty much all of them other than x86), and also prevents
780 * the compiler from reordering the code that initializes the
781 * structure after the pointer assignment. More importantly, this
782 * call documents which pointers will be dereferenced by RCU read-side
785 #define rcu_assign_pointer(p, v) \
786 __rcu_assign_pointer((p), (v), __rcu)
789 * RCU_INIT_POINTER() - initialize an RCU protected pointer
791 * Initialize an RCU-protected pointer in such a way to avoid RCU-lockdep
794 #define RCU_INIT_POINTER(p, v) \
795 p = (typeof(*v) __force __rcu *)(v)
797 static __always_inline
bool __is_kfree_rcu_offset(unsigned long offset
)
799 return offset
< 4096;
802 static __always_inline
803 void __kfree_rcu(struct rcu_head
*head
, unsigned long offset
)
805 typedef void (*rcu_callback
)(struct rcu_head
*);
807 BUILD_BUG_ON(!__builtin_constant_p(offset
));
809 /* See the kfree_rcu() header comment. */
810 BUILD_BUG_ON(!__is_kfree_rcu_offset(offset
));
812 call_rcu(head
, (rcu_callback
)offset
);
816 * kfree_rcu() - kfree an object after a grace period.
817 * @ptr: pointer to kfree
818 * @rcu_head: the name of the struct rcu_head within the type of @ptr.
820 * Many rcu callbacks functions just call kfree() on the base structure.
821 * These functions are trivial, but their size adds up, and furthermore
822 * when they are used in a kernel module, that module must invoke the
823 * high-latency rcu_barrier() function at module-unload time.
825 * The kfree_rcu() function handles this issue. Rather than encoding a
826 * function address in the embedded rcu_head structure, kfree_rcu() instead
827 * encodes the offset of the rcu_head structure within the base structure.
828 * Because the functions are not allowed in the low-order 4096 bytes of
829 * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
830 * If the offset is larger than 4095 bytes, a compile-time error will
831 * be generated in __kfree_rcu(). If this error is triggered, you can
832 * either fall back to use of call_rcu() or rearrange the structure to
833 * position the rcu_head structure into the first 4096 bytes.
835 * Note that the allowable offset might decrease in the future, for example,
836 * to allow something like kmem_cache_free_rcu().
838 #define kfree_rcu(ptr, rcu_head) \
839 __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
841 #endif /* __LINUX_RCUPDATE_H */