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 rcu_barrier(void);
60 extern void rcu_barrier_bh(void);
61 extern void rcu_barrier_sched(void);
62 extern void synchronize_sched_expedited(void);
63 extern int sched_expedited_torture_stats(char *page);
65 /* Internal to kernel */
66 extern void rcu_init(void);
68 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
69 #include <linux/rcutree.h>
70 #elif defined(CONFIG_TINY_RCU)
71 #include <linux/rcutiny.h>
73 #error "Unknown RCU implementation specified to kernel configuration"
76 #define RCU_HEAD_INIT { .next = NULL, .func = NULL }
77 #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
78 #define INIT_RCU_HEAD(ptr) do { \
79 (ptr)->next = NULL; (ptr)->func = NULL; \
82 #ifdef CONFIG_DEBUG_LOCK_ALLOC
84 extern struct lockdep_map rcu_lock_map;
85 # define rcu_read_acquire() \
86 lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
87 # define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_)
89 extern struct lockdep_map rcu_bh_lock_map;
90 # define rcu_read_acquire_bh() \
91 lock_acquire(&rcu_bh_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
92 # define rcu_read_release_bh() lock_release(&rcu_bh_lock_map, 1, _THIS_IP_)
94 extern struct lockdep_map rcu_sched_lock_map;
95 # define rcu_read_acquire_sched() \
96 lock_acquire(&rcu_sched_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
97 # define rcu_read_release_sched() \
98 lock_release(&rcu_sched_lock_map, 1, _THIS_IP_)
100 extern int debug_lockdep_rcu_enabled(void);
103 * rcu_read_lock_held - might we be in RCU read-side critical section?
105 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
106 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
107 * this assumes we are in an RCU read-side critical section unless it can
110 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
111 * and while lockdep is disabled.
113 static inline int rcu_read_lock_held(void)
115 if (!debug_lockdep_rcu_enabled())
117 return lock_is_held(&rcu_lock_map);
121 * rcu_read_lock_bh_held() is defined out of line to avoid #include-file
124 extern int rcu_read_lock_bh_held(void);
127 * rcu_read_lock_sched_held - might we be in RCU-sched read-side critical section?
129 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
130 * RCU-sched read-side critical section. In absence of
131 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
132 * critical section unless it can prove otherwise. Note that disabling
133 * of preemption (including disabling irqs) counts as an RCU-sched
134 * read-side critical section.
136 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
137 * and while lockdep is disabled.
139 #ifdef CONFIG_PREEMPT
140 static inline int rcu_read_lock_sched_held(void)
142 int lockdep_opinion = 0;
144 if (!debug_lockdep_rcu_enabled())
147 lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
148 return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
150 #else /* #ifdef CONFIG_PREEMPT */
151 static inline int rcu_read_lock_sched_held(void)
155 #endif /* #else #ifdef CONFIG_PREEMPT */
157 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
159 # define rcu_read_acquire() do { } while (0)
160 # define rcu_read_release() do { } while (0)
161 # define rcu_read_acquire_bh() do { } while (0)
162 # define rcu_read_release_bh() do { } while (0)
163 # define rcu_read_acquire_sched() do { } while (0)
164 # define rcu_read_release_sched() do { } while (0)
166 static inline int rcu_read_lock_held(void)
171 static inline int rcu_read_lock_bh_held(void)
176 #ifdef CONFIG_PREEMPT
177 static inline int rcu_read_lock_sched_held(void)
179 return preempt_count() != 0 || irqs_disabled();
181 #else /* #ifdef CONFIG_PREEMPT */
182 static inline int rcu_read_lock_sched_held(void)
186 #endif /* #else #ifdef CONFIG_PREEMPT */
188 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
190 #ifdef CONFIG_PROVE_RCU
192 extern int rcu_my_thread_group_empty(void);
194 #define __do_rcu_dereference_check(c) \
196 static bool __warned; \
197 if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
199 lockdep_rcu_dereference(__FILE__, __LINE__); \
204 * rcu_dereference_check - rcu_dereference with debug checking
205 * @p: The pointer to read, prior to dereferencing
206 * @c: The conditions under which the dereference will take place
208 * Do an rcu_dereference(), but check that the conditions under which the
209 * dereference will take place are correct. Typically the conditions indicate
210 * the various locking conditions that should be held at that point. The check
211 * should return true if the conditions are satisfied.
215 * bar = rcu_dereference_check(foo->bar, rcu_read_lock_held() ||
216 * lockdep_is_held(&foo->lock));
218 * could be used to indicate to lockdep that foo->bar may only be dereferenced
219 * if either the RCU read lock is held, or that the lock required to replace
220 * the bar struct at foo->bar is held.
222 * Note that the list of conditions may also include indications of when a lock
223 * need not be held, for example during initialisation or destruction of the
226 * bar = rcu_dereference_check(foo->bar, rcu_read_lock_held() ||
227 * lockdep_is_held(&foo->lock) ||
228 * atomic_read(&foo->usage) == 0);
230 #define rcu_dereference_check(p, c) \
232 __do_rcu_dereference_check(c); \
233 rcu_dereference_raw(p); \
237 * rcu_dereference_protected - fetch RCU pointer when updates prevented
239 * Return the value of the specified RCU-protected pointer, but omit
240 * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This
241 * is useful in cases where update-side locks prevent the value of the
242 * pointer from changing. Please note that this primitive does -not-
243 * prevent the compiler from repeating this reference or combining it
244 * with other references, so it should not be used without protection
245 * of appropriate locks.
247 #define rcu_dereference_protected(p, c) \
249 __do_rcu_dereference_check(c); \
253 #else /* #ifdef CONFIG_PROVE_RCU */
255 #define rcu_dereference_check(p, c) rcu_dereference_raw(p)
256 #define rcu_dereference_protected(p, c) (p)
258 #endif /* #else #ifdef CONFIG_PROVE_RCU */
261 * rcu_access_pointer - fetch RCU pointer with no dereferencing
263 * Return the value of the specified RCU-protected pointer, but omit the
264 * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful
265 * when the value of this pointer is accessed, but the pointer is not
266 * dereferenced, for example, when testing an RCU-protected pointer against
267 * NULL. This may also be used in cases where update-side locks prevent
268 * the value of the pointer from changing, but rcu_dereference_protected()
269 * is a lighter-weight primitive for this use case.
271 #define rcu_access_pointer(p) ACCESS_ONCE(p)
274 * rcu_read_lock - mark the beginning of an RCU read-side critical section.
276 * When synchronize_rcu() is invoked on one CPU while other CPUs
277 * are within RCU read-side critical sections, then the
278 * synchronize_rcu() is guaranteed to block until after all the other
279 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
280 * on one CPU while other CPUs are within RCU read-side critical
281 * sections, invocation of the corresponding RCU callback is deferred
282 * until after the all the other CPUs exit their critical sections.
284 * Note, however, that RCU callbacks are permitted to run concurrently
285 * with RCU read-side critical sections. One way that this can happen
286 * is via the following sequence of events: (1) CPU 0 enters an RCU
287 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
288 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
289 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
290 * callback is invoked. This is legal, because the RCU read-side critical
291 * section that was running concurrently with the call_rcu() (and which
292 * therefore might be referencing something that the corresponding RCU
293 * callback would free up) has completed before the corresponding
294 * RCU callback is invoked.
296 * RCU read-side critical sections may be nested. Any deferred actions
297 * will be deferred until the outermost RCU read-side critical section
300 * It is illegal to block while in an RCU read-side critical section.
302 static inline void rcu_read_lock(void)
310 * So where is rcu_write_lock()? It does not exist, as there is no
311 * way for writers to lock out RCU readers. This is a feature, not
312 * a bug -- this property is what provides RCU's performance benefits.
313 * Of course, writers must coordinate with each other. The normal
314 * spinlock primitives work well for this, but any other technique may be
315 * used as well. RCU does not care how the writers keep out of each
316 * others' way, as long as they do so.
320 * rcu_read_unlock - marks the end of an RCU read-side critical section.
322 * See rcu_read_lock() for more information.
324 static inline void rcu_read_unlock(void)
332 * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
334 * This is equivalent of rcu_read_lock(), but to be used when updates
335 * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
336 * consider completion of a softirq handler to be a quiescent state,
337 * a process in RCU read-side critical section must be protected by
338 * disabling softirqs. Read-side critical sections in interrupt context
339 * can use just rcu_read_lock().
342 static inline void rcu_read_lock_bh(void)
344 __rcu_read_lock_bh();
346 rcu_read_acquire_bh();
350 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
352 * See rcu_read_lock_bh() for more information.
354 static inline void rcu_read_unlock_bh(void)
356 rcu_read_release_bh();
358 __rcu_read_unlock_bh();
362 * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
364 * Should be used with either
365 * - synchronize_sched()
367 * - call_rcu_sched() and rcu_barrier_sched()
368 * on the write-side to insure proper synchronization.
370 static inline void rcu_read_lock_sched(void)
373 __acquire(RCU_SCHED);
374 rcu_read_acquire_sched();
377 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
378 static inline notrace void rcu_read_lock_sched_notrace(void)
380 preempt_disable_notrace();
381 __acquire(RCU_SCHED);
385 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
387 * See rcu_read_lock_sched for more information.
389 static inline void rcu_read_unlock_sched(void)
391 rcu_read_release_sched();
392 __release(RCU_SCHED);
396 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
397 static inline notrace void rcu_read_unlock_sched_notrace(void)
399 __release(RCU_SCHED);
400 preempt_enable_notrace();
405 * rcu_dereference_raw - fetch an RCU-protected pointer
407 * The caller must be within some flavor of RCU read-side critical
408 * section, or must be otherwise preventing the pointer from changing,
409 * for example, by holding an appropriate lock. This pointer may later
410 * be safely dereferenced. It is the caller's responsibility to have
411 * done the right thing, as this primitive does no checking of any kind.
413 * Inserts memory barriers on architectures that require them
414 * (currently only the Alpha), and, more importantly, documents
415 * exactly which pointers are protected by RCU.
417 #define rcu_dereference_raw(p) ({ \
418 typeof(p) _________p1 = ACCESS_ONCE(p); \
419 smp_read_barrier_depends(); \
424 * rcu_dereference - fetch an RCU-protected pointer, checking for RCU
426 * Makes rcu_dereference_check() do the dirty work.
428 #define rcu_dereference(p) \
429 rcu_dereference_check(p, rcu_read_lock_held())
432 * rcu_dereference_bh - fetch an RCU-protected pointer, checking for RCU-bh
434 * Makes rcu_dereference_check() do the dirty work.
436 #define rcu_dereference_bh(p) \
437 rcu_dereference_check(p, rcu_read_lock_bh_held())
440 * rcu_dereference_sched - fetch RCU-protected pointer, checking for RCU-sched
442 * Makes rcu_dereference_check() do the dirty work.
444 #define rcu_dereference_sched(p) \
445 rcu_dereference_check(p, rcu_read_lock_sched_held())
448 * rcu_assign_pointer - assign (publicize) a pointer to a newly
449 * initialized structure that will be dereferenced by RCU read-side
450 * critical sections. Returns the value assigned.
452 * Inserts memory barriers on architectures that require them
453 * (pretty much all of them other than x86), and also prevents
454 * the compiler from reordering the code that initializes the
455 * structure after the pointer assignment. More importantly, this
456 * call documents which pointers will be dereferenced by RCU read-side
460 #define rcu_assign_pointer(p, v) \
462 if (!__builtin_constant_p(v) || \
468 /* Infrastructure to implement the synchronize_() primitives. */
470 struct rcu_synchronize {
471 struct rcu_head head;
472 struct completion completion;
475 extern void wakeme_after_rcu(struct rcu_head *head);
478 * call_rcu - Queue an RCU callback for invocation after a grace period.
479 * @head: structure to be used for queueing the RCU updates.
480 * @func: actual update function to be invoked after the grace period
482 * The update function will be invoked some time after a full grace
483 * period elapses, in other words after all currently executing RCU
484 * read-side critical sections have completed. RCU read-side critical
485 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
488 extern void call_rcu(struct rcu_head *head,
489 void (*func)(struct rcu_head *head));
492 * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
493 * @head: structure to be used for queueing the RCU updates.
494 * @func: actual update function to be invoked after the grace period
496 * The update function will be invoked some time after a full grace
497 * period elapses, in other words after all currently executing RCU
498 * read-side critical sections have completed. call_rcu_bh() assumes
499 * that the read-side critical sections end on completion of a softirq
500 * handler. This means that read-side critical sections in process
501 * context must not be interrupted by softirqs. This interface is to be
502 * used when most of the read-side critical sections are in softirq context.
503 * RCU read-side critical sections are delimited by :
504 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
506 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
507 * These may be nested.
509 extern void call_rcu_bh(struct rcu_head *head,
510 void (*func)(struct rcu_head *head));
512 #endif /* __LINUX_RCUPDATE_H */