2 * Read-Copy Update mechanism for mutual exclusion
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
18 * Copyright IBM Corporation, 2001
20 * Author: Dipankar Sarma <dipankar@in.ibm.com>
22 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
23 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
25 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
26 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
28 * For detailed explanation of Read-Copy Update mechanism see -
29 * http://lse.sourceforge.net/locking/rcupdate.html
33 #ifndef __LINUX_RCUPDATE_H
34 #define __LINUX_RCUPDATE_H
36 #include <linux/cache.h>
37 #include <linux/spinlock.h>
38 #include <linux/threads.h>
39 #include <linux/cpumask.h>
40 #include <linux/seqlock.h>
41 #include <linux/lockdep.h>
42 #include <linux/completion.h>
44 #ifdef CONFIG_RCU_TORTURE_TEST
45 extern int rcutorture_runnable; /* for sysctl */
46 #endif /* #ifdef CONFIG_RCU_TORTURE_TEST */
49 * struct rcu_head - callback structure for use with RCU
50 * @next: next update requests in a list
51 * @func: actual update function to call after the grace period.
54 struct rcu_head *next;
55 void (*func)(struct rcu_head *head);
58 /* Exported common interfaces */
59 extern void synchronize_rcu_bh(void);
60 extern void synchronize_sched(void);
61 extern void rcu_barrier(void);
62 extern void rcu_barrier_bh(void);
63 extern void rcu_barrier_sched(void);
64 extern void synchronize_sched_expedited(void);
65 extern int sched_expedited_torture_stats(char *page);
67 /* Internal to kernel */
68 extern void rcu_init(void);
69 extern int rcu_scheduler_active;
70 extern void rcu_scheduler_starting(void);
72 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
73 #include <linux/rcutree.h>
74 #elif defined(CONFIG_TINY_RCU)
75 #include <linux/rcutiny.h>
77 #error "Unknown RCU implementation specified to kernel configuration"
80 #define RCU_HEAD_INIT { .next = NULL, .func = NULL }
81 #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
82 #define INIT_RCU_HEAD(ptr) do { \
83 (ptr)->next = NULL; (ptr)->func = NULL; \
86 #ifdef CONFIG_DEBUG_LOCK_ALLOC
88 extern struct lockdep_map rcu_lock_map;
89 # define rcu_read_acquire() \
90 lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
91 # define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_)
93 extern struct lockdep_map rcu_bh_lock_map;
94 # define rcu_read_acquire_bh() \
95 lock_acquire(&rcu_bh_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
96 # define rcu_read_release_bh() lock_release(&rcu_bh_lock_map, 1, _THIS_IP_)
98 extern struct lockdep_map rcu_sched_lock_map;
99 # define rcu_read_acquire_sched() \
100 lock_acquire(&rcu_sched_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
101 # define rcu_read_release_sched() \
102 lock_release(&rcu_sched_lock_map, 1, _THIS_IP_)
104 extern int debug_lockdep_rcu_enabled(void);
107 * rcu_read_lock_held - might we be in RCU read-side critical section?
109 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
110 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
111 * this assumes we are in an RCU read-side critical section unless it can
114 * Check rcu_scheduler_active to prevent false positives during boot.
116 static inline int rcu_read_lock_held(void)
118 if (!debug_lockdep_rcu_enabled())
120 return lock_is_held(&rcu_lock_map);
124 * rcu_read_lock_bh_held() is defined out of line to avoid #include-file
127 extern int rcu_read_lock_bh_held(void);
130 * rcu_read_lock_sched_held - might we be in RCU-sched read-side critical section?
132 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
133 * RCU-sched read-side critical section. In absence of
134 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
135 * critical section unless it can prove otherwise. Note that disabling
136 * of preemption (including disabling irqs) counts as an RCU-sched
137 * read-side critical section.
139 * Check rcu_scheduler_active to prevent false positives during boot.
141 #ifdef CONFIG_PREEMPT
142 static inline int rcu_read_lock_sched_held(void)
144 int lockdep_opinion = 0;
146 if (!debug_lockdep_rcu_enabled())
149 lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
150 return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
152 #else /* #ifdef CONFIG_PREEMPT */
153 static inline int rcu_read_lock_sched_held(void)
157 #endif /* #else #ifdef CONFIG_PREEMPT */
159 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
161 # define rcu_read_acquire() do { } while (0)
162 # define rcu_read_release() do { } while (0)
163 # define rcu_read_acquire_bh() do { } while (0)
164 # define rcu_read_release_bh() do { } while (0)
165 # define rcu_read_acquire_sched() do { } while (0)
166 # define rcu_read_release_sched() do { } while (0)
168 static inline int rcu_read_lock_held(void)
173 static inline int rcu_read_lock_bh_held(void)
178 #ifdef CONFIG_PREEMPT
179 static inline int rcu_read_lock_sched_held(void)
181 return !rcu_scheduler_active || preempt_count() != 0 || irqs_disabled();
183 #else /* #ifdef CONFIG_PREEMPT */
184 static inline int rcu_read_lock_sched_held(void)
188 #endif /* #else #ifdef CONFIG_PREEMPT */
190 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
192 #ifdef CONFIG_PROVE_RCU
194 extern int rcu_my_thread_group_empty(void);
196 #define __do_rcu_dereference_check(c) \
198 static bool __warned; \
199 if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
201 lockdep_rcu_dereference(__FILE__, __LINE__); \
206 * rcu_dereference_check - rcu_dereference with debug checking
207 * @p: The pointer to read, prior to dereferencing
208 * @c: The conditions under which the dereference will take place
210 * Do an rcu_dereference(), but check that the conditions under which the
211 * dereference will take place are correct. Typically the conditions indicate
212 * the various locking conditions that should be held at that point. The check
213 * should return true if the conditions are satisfied.
217 * bar = rcu_dereference_check(foo->bar, rcu_read_lock_held() ||
218 * lockdep_is_held(&foo->lock));
220 * could be used to indicate to lockdep that foo->bar may only be dereferenced
221 * if either the RCU read lock is held, or that the lock required to replace
222 * the bar struct at foo->bar is held.
224 * Note that the list of conditions may also include indications of when a lock
225 * need not be held, for example during initialisation or destruction of the
228 * bar = rcu_dereference_check(foo->bar, rcu_read_lock_held() ||
229 * lockdep_is_held(&foo->lock) ||
230 * atomic_read(&foo->usage) == 0);
232 #define rcu_dereference_check(p, c) \
234 __do_rcu_dereference_check(c); \
235 rcu_dereference_raw(p); \
239 * rcu_dereference_protected - fetch RCU pointer when updates prevented
241 * Return the value of the specified RCU-protected pointer, but omit
242 * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This
243 * is useful in cases where update-side locks prevent the value of the
244 * pointer from changing. Please note that this primitive does -not-
245 * prevent the compiler from repeating this reference or combining it
246 * with other references, so it should not be used without protection
247 * of appropriate locks.
249 #define rcu_dereference_protected(p, c) \
251 __do_rcu_dereference_check(c); \
255 #else /* #ifdef CONFIG_PROVE_RCU */
257 #define rcu_dereference_check(p, c) rcu_dereference_raw(p)
258 #define rcu_dereference_protected(p, c) (p)
260 #endif /* #else #ifdef CONFIG_PROVE_RCU */
263 * rcu_access_pointer - fetch RCU pointer with no dereferencing
265 * Return the value of the specified RCU-protected pointer, but omit the
266 * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful
267 * when the value of this pointer is accessed, but the pointer is not
268 * dereferenced, for example, when testing an RCU-protected pointer against
269 * NULL. This may also be used in cases where update-side locks prevent
270 * the value of the pointer from changing, but rcu_dereference_protected()
271 * is a lighter-weight primitive for this use case.
273 #define rcu_access_pointer(p) ACCESS_ONCE(p)
276 * rcu_read_lock - mark the beginning of an RCU read-side critical section.
278 * When synchronize_rcu() is invoked on one CPU while other CPUs
279 * are within RCU read-side critical sections, then the
280 * synchronize_rcu() is guaranteed to block until after all the other
281 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
282 * on one CPU while other CPUs are within RCU read-side critical
283 * sections, invocation of the corresponding RCU callback is deferred
284 * until after the all the other CPUs exit their critical sections.
286 * Note, however, that RCU callbacks are permitted to run concurrently
287 * with RCU read-side critical sections. One way that this can happen
288 * is via the following sequence of events: (1) CPU 0 enters an RCU
289 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
290 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
291 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
292 * callback is invoked. This is legal, because the RCU read-side critical
293 * section that was running concurrently with the call_rcu() (and which
294 * therefore might be referencing something that the corresponding RCU
295 * callback would free up) has completed before the corresponding
296 * RCU callback is invoked.
298 * RCU read-side critical sections may be nested. Any deferred actions
299 * will be deferred until the outermost RCU read-side critical section
302 * It is illegal to block while in an RCU read-side critical section.
304 static inline void rcu_read_lock(void)
312 * So where is rcu_write_lock()? It does not exist, as there is no
313 * way for writers to lock out RCU readers. This is a feature, not
314 * a bug -- this property is what provides RCU's performance benefits.
315 * Of course, writers must coordinate with each other. The normal
316 * spinlock primitives work well for this, but any other technique may be
317 * used as well. RCU does not care how the writers keep out of each
318 * others' way, as long as they do so.
322 * rcu_read_unlock - marks the end of an RCU read-side critical section.
324 * See rcu_read_lock() for more information.
326 static inline void rcu_read_unlock(void)
334 * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
336 * This is equivalent of rcu_read_lock(), but to be used when updates
337 * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
338 * consider completion of a softirq handler to be a quiescent state,
339 * a process in RCU read-side critical section must be protected by
340 * disabling softirqs. Read-side critical sections in interrupt context
341 * can use just rcu_read_lock().
344 static inline void rcu_read_lock_bh(void)
346 __rcu_read_lock_bh();
348 rcu_read_acquire_bh();
352 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
354 * See rcu_read_lock_bh() for more information.
356 static inline void rcu_read_unlock_bh(void)
358 rcu_read_release_bh();
360 __rcu_read_unlock_bh();
364 * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
366 * Should be used with either
367 * - synchronize_sched()
369 * - call_rcu_sched() and rcu_barrier_sched()
370 * on the write-side to insure proper synchronization.
372 static inline void rcu_read_lock_sched(void)
375 __acquire(RCU_SCHED);
376 rcu_read_acquire_sched();
379 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
380 static inline notrace void rcu_read_lock_sched_notrace(void)
382 preempt_disable_notrace();
383 __acquire(RCU_SCHED);
387 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
389 * See rcu_read_lock_sched for more information.
391 static inline void rcu_read_unlock_sched(void)
393 rcu_read_release_sched();
394 __release(RCU_SCHED);
398 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
399 static inline notrace void rcu_read_unlock_sched_notrace(void)
401 __release(RCU_SCHED);
402 preempt_enable_notrace();
407 * rcu_dereference_raw - fetch an RCU-protected pointer
409 * The caller must be within some flavor of RCU read-side critical
410 * section, or must be otherwise preventing the pointer from changing,
411 * for example, by holding an appropriate lock. This pointer may later
412 * be safely dereferenced. It is the caller's responsibility to have
413 * done the right thing, as this primitive does no checking of any kind.
415 * Inserts memory barriers on architectures that require them
416 * (currently only the Alpha), and, more importantly, documents
417 * exactly which pointers are protected by RCU.
419 #define rcu_dereference_raw(p) ({ \
420 typeof(p) _________p1 = ACCESS_ONCE(p); \
421 smp_read_barrier_depends(); \
426 * rcu_dereference - fetch an RCU-protected pointer, checking for RCU
428 * Makes rcu_dereference_check() do the dirty work.
430 #define rcu_dereference(p) \
431 rcu_dereference_check(p, rcu_read_lock_held())
434 * rcu_dereference_bh - fetch an RCU-protected pointer, checking for RCU-bh
436 * Makes rcu_dereference_check() do the dirty work.
438 #define rcu_dereference_bh(p) \
439 rcu_dereference_check(p, rcu_read_lock_bh_held())
442 * rcu_dereference_sched - fetch RCU-protected pointer, checking for RCU-sched
444 * Makes rcu_dereference_check() do the dirty work.
446 #define rcu_dereference_sched(p) \
447 rcu_dereference_check(p, rcu_read_lock_sched_held())
450 * rcu_assign_pointer - assign (publicize) a pointer to a newly
451 * initialized structure that will be dereferenced by RCU read-side
452 * critical sections. Returns the value assigned.
454 * Inserts memory barriers on architectures that require them
455 * (pretty much all of them other than x86), and also prevents
456 * the compiler from reordering the code that initializes the
457 * structure after the pointer assignment. More importantly, this
458 * call documents which pointers will be dereferenced by RCU read-side
462 #define rcu_assign_pointer(p, v) \
464 if (!__builtin_constant_p(v) || \
470 /* Infrastructure to implement the synchronize_() primitives. */
472 struct rcu_synchronize {
473 struct rcu_head head;
474 struct completion completion;
477 extern void wakeme_after_rcu(struct rcu_head *head);
480 * call_rcu - Queue an RCU callback for invocation after a grace period.
481 * @head: structure to be used for queueing the RCU updates.
482 * @func: actual update function to be invoked after the grace period
484 * The update function will be invoked some time after a full grace
485 * period elapses, in other words after all currently executing RCU
486 * read-side critical sections have completed. RCU read-side critical
487 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
490 extern void call_rcu(struct rcu_head *head,
491 void (*func)(struct rcu_head *head));
494 * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
495 * @head: structure to be used for queueing the RCU updates.
496 * @func: actual update function to be invoked after the grace period
498 * The update function will be invoked some time after a full grace
499 * period elapses, in other words after all currently executing RCU
500 * read-side critical sections have completed. call_rcu_bh() assumes
501 * that the read-side critical sections end on completion of a softirq
502 * handler. This means that read-side critical sections in process
503 * context must not be interrupted by softirqs. This interface is to be
504 * used when most of the read-side critical sections are in softirq context.
505 * RCU read-side critical sections are delimited by :
506 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
508 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
509 * These may be nested.
511 extern void call_rcu_bh(struct rcu_head *head,
512 void (*func)(struct rcu_head *head));
514 #endif /* __LINUX_RCUPDATE_H */