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_PROVE_LOCKING is selected and enabled, returns nonzero iff in
110 * an RCU read-side critical section. In absence of CONFIG_PROVE_LOCKING,
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_PROVE_LOCKING is selected and enabled, returns nonzero iff in an
133 * RCU-sched read-side critical section. In absence of CONFIG_PROVE_LOCKING,
134 * this assumes we are in an RCU-sched read-side critical section unless it
135 * can prove otherwise. Note that disabling of preemption (including
136 * disabling irqs) counts as an RCU-sched read-side critical section.
138 * Check rcu_scheduler_active to prevent false positives during boot.
140 #ifdef CONFIG_PREEMPT
141 static inline int rcu_read_lock_sched_held(void)
143 int lockdep_opinion
= 0;
145 if (!debug_lockdep_rcu_enabled())
148 lockdep_opinion
= lock_is_held(&rcu_sched_lock_map
);
149 return lockdep_opinion
|| preempt_count() != 0 || irqs_disabled();
151 #else /* #ifdef CONFIG_PREEMPT */
152 static inline int rcu_read_lock_sched_held(void)
156 #endif /* #else #ifdef CONFIG_PREEMPT */
158 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
160 # define rcu_read_acquire() do { } while (0)
161 # define rcu_read_release() do { } while (0)
162 # define rcu_read_acquire_bh() do { } while (0)
163 # define rcu_read_release_bh() do { } while (0)
164 # define rcu_read_acquire_sched() do { } while (0)
165 # define rcu_read_release_sched() do { } while (0)
167 static inline int rcu_read_lock_held(void)
172 static inline int rcu_read_lock_bh_held(void)
177 #ifdef CONFIG_PREEMPT
178 static inline int rcu_read_lock_sched_held(void)
180 return !rcu_scheduler_active
|| preempt_count() != 0 || irqs_disabled();
182 #else /* #ifdef CONFIG_PREEMPT */
183 static inline int rcu_read_lock_sched_held(void)
187 #endif /* #else #ifdef CONFIG_PREEMPT */
189 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
191 #ifdef CONFIG_PROVE_RCU
193 extern int rcu_my_thread_group_empty(void);
195 #define __do_rcu_dereference_check(c) \
197 static bool __warned; \
198 if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
200 lockdep_rcu_dereference(__FILE__, __LINE__); \
205 * rcu_dereference_check - rcu_dereference with debug checking
206 * @p: The pointer to read, prior to dereferencing
207 * @c: The conditions under which the dereference will take place
209 * Do an rcu_dereference(), but check that the conditions under which the
210 * dereference will take place are correct. Typically the conditions indicate
211 * the various locking conditions that should be held at that point. The check
212 * should return true if the conditions are satisfied.
216 * bar = rcu_dereference_check(foo->bar, rcu_read_lock_held() ||
217 * lockdep_is_held(&foo->lock));
219 * could be used to indicate to lockdep that foo->bar may only be dereferenced
220 * if either the RCU read lock is held, or that the lock required to replace
221 * the bar struct at foo->bar is held.
223 * Note that the list of conditions may also include indications of when a lock
224 * need not be held, for example during initialisation or destruction of the
227 * bar = rcu_dereference_check(foo->bar, rcu_read_lock_held() ||
228 * lockdep_is_held(&foo->lock) ||
229 * atomic_read(&foo->usage) == 0);
231 #define rcu_dereference_check(p, c) \
233 __do_rcu_dereference_check(c); \
234 rcu_dereference_raw(p); \
238 * rcu_dereference_protected - fetch RCU pointer when updates prevented
240 * Return the value of the specified RCU-protected pointer, but omit
241 * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This
242 * is useful in cases where update-side locks prevent the value of the
243 * pointer from changing. Please note that this primitive does -not-
244 * prevent the compiler from repeating this reference or combining it
245 * with other references, so it should not be used without protection
246 * of appropriate locks.
248 #define rcu_dereference_protected(p, c) \
250 __do_rcu_dereference_check(c); \
254 #else /* #ifdef CONFIG_PROVE_RCU */
256 #define rcu_dereference_check(p, c) rcu_dereference_raw(p)
257 #define rcu_dereference_protected(p, c) (p)
259 #endif /* #else #ifdef CONFIG_PROVE_RCU */
262 * rcu_access_pointer - fetch RCU pointer with no dereferencing
264 * Return the value of the specified RCU-protected pointer, but omit the
265 * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful
266 * when the value of this pointer is accessed, but the pointer is not
267 * dereferenced, for example, when testing an RCU-protected pointer against
268 * NULL. This may also be used in cases where update-side locks prevent
269 * the value of the pointer from changing, but rcu_dereference_protected()
270 * is a lighter-weight primitive for this use case.
272 #define rcu_access_pointer(p) ACCESS_ONCE(p)
275 * rcu_read_lock - mark the beginning of an RCU read-side critical section.
277 * When synchronize_rcu() is invoked on one CPU while other CPUs
278 * are within RCU read-side critical sections, then the
279 * synchronize_rcu() is guaranteed to block until after all the other
280 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
281 * on one CPU while other CPUs are within RCU read-side critical
282 * sections, invocation of the corresponding RCU callback is deferred
283 * until after the all the other CPUs exit their critical sections.
285 * Note, however, that RCU callbacks are permitted to run concurrently
286 * with RCU read-side critical sections. One way that this can happen
287 * is via the following sequence of events: (1) CPU 0 enters an RCU
288 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
289 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
290 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
291 * callback is invoked. This is legal, because the RCU read-side critical
292 * section that was running concurrently with the call_rcu() (and which
293 * therefore might be referencing something that the corresponding RCU
294 * callback would free up) has completed before the corresponding
295 * RCU callback is invoked.
297 * RCU read-side critical sections may be nested. Any deferred actions
298 * will be deferred until the outermost RCU read-side critical section
301 * It is illegal to block while in an RCU read-side critical section.
303 static inline void rcu_read_lock(void)
311 * So where is rcu_write_lock()? It does not exist, as there is no
312 * way for writers to lock out RCU readers. This is a feature, not
313 * a bug -- this property is what provides RCU's performance benefits.
314 * Of course, writers must coordinate with each other. The normal
315 * spinlock primitives work well for this, but any other technique may be
316 * used as well. RCU does not care how the writers keep out of each
317 * others' way, as long as they do so.
321 * rcu_read_unlock - marks the end of an RCU read-side critical section.
323 * See rcu_read_lock() for more information.
325 static inline void rcu_read_unlock(void)
333 * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
335 * This is equivalent of rcu_read_lock(), but to be used when updates
336 * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
337 * consider completion of a softirq handler to be a quiescent state,
338 * a process in RCU read-side critical section must be protected by
339 * disabling softirqs. Read-side critical sections in interrupt context
340 * can use just rcu_read_lock().
343 static inline void rcu_read_lock_bh(void)
345 __rcu_read_lock_bh();
347 rcu_read_acquire_bh();
351 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
353 * See rcu_read_lock_bh() for more information.
355 static inline void rcu_read_unlock_bh(void)
357 rcu_read_release_bh();
359 __rcu_read_unlock_bh();
363 * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
365 * Should be used with either
366 * - synchronize_sched()
368 * - call_rcu_sched() and rcu_barrier_sched()
369 * on the write-side to insure proper synchronization.
371 static inline void rcu_read_lock_sched(void)
374 __acquire(RCU_SCHED
);
375 rcu_read_acquire_sched();
378 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
379 static inline notrace
void rcu_read_lock_sched_notrace(void)
381 preempt_disable_notrace();
382 __acquire(RCU_SCHED
);
386 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
388 * See rcu_read_lock_sched for more information.
390 static inline void rcu_read_unlock_sched(void)
392 rcu_read_release_sched();
393 __release(RCU_SCHED
);
397 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
398 static inline notrace
void rcu_read_unlock_sched_notrace(void)
400 __release(RCU_SCHED
);
401 preempt_enable_notrace();
406 * rcu_dereference_raw - fetch an RCU-protected pointer
408 * The caller must be within some flavor of RCU read-side critical
409 * section, or must be otherwise preventing the pointer from changing,
410 * for example, by holding an appropriate lock. This pointer may later
411 * be safely dereferenced. It is the caller's responsibility to have
412 * done the right thing, as this primitive does no checking of any kind.
414 * Inserts memory barriers on architectures that require them
415 * (currently only the Alpha), and, more importantly, documents
416 * exactly which pointers are protected by RCU.
418 #define rcu_dereference_raw(p) ({ \
419 typeof(p) _________p1 = ACCESS_ONCE(p); \
420 smp_read_barrier_depends(); \
425 * rcu_dereference - fetch an RCU-protected pointer, checking for RCU
427 * Makes rcu_dereference_check() do the dirty work.
429 #define rcu_dereference(p) \
430 rcu_dereference_check(p, rcu_read_lock_held())
433 * rcu_dereference_bh - fetch an RCU-protected pointer, checking for RCU-bh
435 * Makes rcu_dereference_check() do the dirty work.
437 #define rcu_dereference_bh(p) \
438 rcu_dereference_check(p, rcu_read_lock_bh_held())
441 * rcu_dereference_sched - fetch RCU-protected pointer, checking for RCU-sched
443 * Makes rcu_dereference_check() do the dirty work.
445 #define rcu_dereference_sched(p) \
446 rcu_dereference_check(p, rcu_read_lock_sched_held())
449 * rcu_assign_pointer - assign (publicize) a pointer to a newly
450 * initialized structure that will be dereferenced by RCU read-side
451 * critical sections. Returns the value assigned.
453 * Inserts memory barriers on architectures that require them
454 * (pretty much all of them other than x86), and also prevents
455 * the compiler from reordering the code that initializes the
456 * structure after the pointer assignment. More importantly, this
457 * call documents which pointers will be dereferenced by RCU read-side
461 #define rcu_assign_pointer(p, v) \
463 if (!__builtin_constant_p(v) || \
469 /* Infrastructure to implement the synchronize_() primitives. */
471 struct rcu_synchronize
{
472 struct rcu_head head
;
473 struct completion completion
;
476 extern void wakeme_after_rcu(struct rcu_head
*head
);
479 * call_rcu - Queue an RCU callback for invocation after a grace period.
480 * @head: structure to be used for queueing the RCU updates.
481 * @func: actual update function to be invoked after the grace period
483 * The update function will be invoked some time after a full grace
484 * period elapses, in other words after all currently executing RCU
485 * read-side critical sections have completed. RCU read-side critical
486 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
489 extern void call_rcu(struct rcu_head
*head
,
490 void (*func
)(struct rcu_head
*head
));
493 * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
494 * @head: structure to be used for queueing the RCU updates.
495 * @func: actual update function to be invoked after the grace period
497 * The update function will be invoked some time after a full grace
498 * period elapses, in other words after all currently executing RCU
499 * read-side critical sections have completed. call_rcu_bh() assumes
500 * that the read-side critical sections end on completion of a softirq
501 * handler. This means that read-side critical sections in process
502 * context must not be interrupted by softirqs. This interface is to be
503 * used when most of the read-side critical sections are in softirq context.
504 * RCU read-side critical sections are delimited by :
505 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
507 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
508 * These may be nested.
510 extern void call_rcu_bh(struct rcu_head
*head
,
511 void (*func
)(struct rcu_head
*head
));
513 #endif /* __LINUX_RCUPDATE_H */