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>
45 * struct rcu_head - callback structure for use with RCU
46 * @next: next update requests in a list
47 * @func: actual update function to call after the grace period.
50 struct rcu_head *next;
51 void (*func)(struct rcu_head *head);
54 /* Exported common interfaces */
55 extern void synchronize_rcu_bh(void);
56 extern void synchronize_sched(void);
57 extern void rcu_barrier(void);
58 extern void rcu_barrier_bh(void);
59 extern void rcu_barrier_sched(void);
60 extern void synchronize_sched_expedited(void);
61 extern int sched_expedited_torture_stats(char *page);
63 /* Internal to kernel */
64 extern void rcu_init(void);
65 extern int rcu_scheduler_active;
66 extern void rcu_scheduler_starting(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 static inline int debug_lockdep_rcu_enabled(void)
102 return likely(rcu_scheduler_active && debug_locks);
106 * rcu_read_lock_held - might we be in RCU read-side critical section?
108 * If CONFIG_PROVE_LOCKING is selected and enabled, returns nonzero iff in
109 * an RCU read-side critical section. In absence of CONFIG_PROVE_LOCKING,
110 * this assumes we are in an RCU read-side critical section unless it can
113 * Check rcu_scheduler_active to prevent false positives during boot.
115 static inline int rcu_read_lock_held(void)
117 if (!debug_lockdep_rcu_enabled())
119 return lock_is_held(&rcu_lock_map);
123 * rcu_read_lock_bh_held - might we be in RCU-bh read-side critical section?
125 * If CONFIG_PROVE_LOCKING is selected and enabled, returns nonzero iff in
126 * an RCU-bh read-side critical section. In absence of CONFIG_PROVE_LOCKING,
127 * this assumes we are in an RCU-bh read-side critical section unless it can
130 * Check rcu_scheduler_active to prevent false positives during boot.
132 static inline int rcu_read_lock_bh_held(void)
134 if (!debug_lockdep_rcu_enabled())
136 return lock_is_held(&rcu_bh_lock_map);
140 * rcu_read_lock_sched_held - might we be in RCU-sched read-side critical section?
142 * If CONFIG_PROVE_LOCKING is selected and enabled, returns nonzero iff in an
143 * RCU-sched read-side critical section. In absence of CONFIG_PROVE_LOCKING,
144 * this assumes we are in an RCU-sched read-side critical section unless it
145 * can prove otherwise. Note that disabling of preemption (including
146 * disabling irqs) counts as an RCU-sched read-side critical section.
148 * Check rcu_scheduler_active to prevent false positives during boot.
150 #ifdef CONFIG_PREEMPT
151 static inline int rcu_read_lock_sched_held(void)
153 int lockdep_opinion = 0;
155 if (!debug_lockdep_rcu_enabled())
158 lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
159 return lockdep_opinion || preempt_count() != 0;
161 #else /* #ifdef CONFIG_PREEMPT */
162 static inline int rcu_read_lock_sched_held(void)
166 #endif /* #else #ifdef CONFIG_PREEMPT */
168 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
170 # define rcu_read_acquire() do { } while (0)
171 # define rcu_read_release() do { } while (0)
172 # define rcu_read_acquire_bh() do { } while (0)
173 # define rcu_read_release_bh() do { } while (0)
174 # define rcu_read_acquire_sched() do { } while (0)
175 # define rcu_read_release_sched() do { } while (0)
177 static inline int rcu_read_lock_held(void)
182 static inline int rcu_read_lock_bh_held(void)
187 #ifdef CONFIG_PREEMPT
188 static inline int rcu_read_lock_sched_held(void)
190 return !rcu_scheduler_active || preempt_count() != 0;
192 #else /* #ifdef CONFIG_PREEMPT */
193 static inline int rcu_read_lock_sched_held(void)
197 #endif /* #else #ifdef CONFIG_PREEMPT */
199 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
201 #ifdef CONFIG_PROVE_RCU
204 * rcu_dereference_check - rcu_dereference with debug checking
206 * Do an rcu_dereference(), but check that the context is correct.
207 * For example, rcu_dereference_check(gp, rcu_read_lock_held()) to
208 * ensure that the rcu_dereference_check() executes within an RCU
209 * read-side critical section. It is also possible to check for
210 * locks being held, for example, by using lockdep_is_held().
212 #define rcu_dereference_check(p, c) \
214 if (debug_lockdep_rcu_enabled() && !(c)) \
215 lockdep_rcu_dereference(__FILE__, __LINE__); \
216 rcu_dereference_raw(p); \
219 #else /* #ifdef CONFIG_PROVE_RCU */
221 #define rcu_dereference_check(p, c) rcu_dereference_raw(p)
223 #endif /* #else #ifdef CONFIG_PROVE_RCU */
226 * rcu_read_lock - mark the beginning of an RCU read-side critical section.
228 * When synchronize_rcu() is invoked on one CPU while other CPUs
229 * are within RCU read-side critical sections, then the
230 * synchronize_rcu() is guaranteed to block until after all the other
231 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
232 * on one CPU while other CPUs are within RCU read-side critical
233 * sections, invocation of the corresponding RCU callback is deferred
234 * until after the all the other CPUs exit their critical sections.
236 * Note, however, that RCU callbacks are permitted to run concurrently
237 * with RCU read-side critical sections. One way that this can happen
238 * is via the following sequence of events: (1) CPU 0 enters an RCU
239 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
240 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
241 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
242 * callback is invoked. This is legal, because the RCU read-side critical
243 * section that was running concurrently with the call_rcu() (and which
244 * therefore might be referencing something that the corresponding RCU
245 * callback would free up) has completed before the corresponding
246 * RCU callback is invoked.
248 * RCU read-side critical sections may be nested. Any deferred actions
249 * will be deferred until the outermost RCU read-side critical section
252 * It is illegal to block while in an RCU read-side critical section.
254 static inline void rcu_read_lock(void)
262 * So where is rcu_write_lock()? It does not exist, as there is no
263 * way for writers to lock out RCU readers. This is a feature, not
264 * a bug -- this property is what provides RCU's performance benefits.
265 * Of course, writers must coordinate with each other. The normal
266 * spinlock primitives work well for this, but any other technique may be
267 * used as well. RCU does not care how the writers keep out of each
268 * others' way, as long as they do so.
272 * rcu_read_unlock - marks the end of an RCU read-side critical section.
274 * See rcu_read_lock() for more information.
276 static inline void rcu_read_unlock(void)
284 * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
286 * This is equivalent of rcu_read_lock(), but to be used when updates
287 * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
288 * consider completion of a softirq handler to be a quiescent state,
289 * a process in RCU read-side critical section must be protected by
290 * disabling softirqs. Read-side critical sections in interrupt context
291 * can use just rcu_read_lock().
294 static inline void rcu_read_lock_bh(void)
296 __rcu_read_lock_bh();
298 rcu_read_acquire_bh();
302 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
304 * See rcu_read_lock_bh() for more information.
306 static inline void rcu_read_unlock_bh(void)
308 rcu_read_release_bh();
310 __rcu_read_unlock_bh();
314 * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
316 * Should be used with either
317 * - synchronize_sched()
319 * - call_rcu_sched() and rcu_barrier_sched()
320 * on the write-side to insure proper synchronization.
322 static inline void rcu_read_lock_sched(void)
325 __acquire(RCU_SCHED);
326 rcu_read_acquire_sched();
329 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
330 static inline notrace void rcu_read_lock_sched_notrace(void)
332 preempt_disable_notrace();
333 __acquire(RCU_SCHED);
337 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
339 * See rcu_read_lock_sched for more information.
341 static inline void rcu_read_unlock_sched(void)
343 rcu_read_release_sched();
344 __release(RCU_SCHED);
348 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
349 static inline notrace void rcu_read_unlock_sched_notrace(void)
351 __release(RCU_SCHED);
352 preempt_enable_notrace();
357 * rcu_dereference_raw - fetch an RCU-protected pointer
359 * The caller must be within some flavor of RCU read-side critical
360 * section, or must be otherwise preventing the pointer from changing,
361 * for example, by holding an appropriate lock. This pointer may later
362 * be safely dereferenced. It is the caller's responsibility to have
363 * done the right thing, as this primitive does no checking of any kind.
365 * Inserts memory barriers on architectures that require them
366 * (currently only the Alpha), and, more importantly, documents
367 * exactly which pointers are protected by RCU.
369 #define rcu_dereference_raw(p) ({ \
370 typeof(p) _________p1 = ACCESS_ONCE(p); \
371 smp_read_barrier_depends(); \
376 * rcu_dereference - fetch an RCU-protected pointer, checking for RCU
378 * Makes rcu_dereference_check() do the dirty work.
380 #define rcu_dereference(p) \
381 rcu_dereference_check(p, rcu_read_lock_held())
384 * rcu_dereference_bh - fetch an RCU-protected pointer, checking for RCU-bh
386 * Makes rcu_dereference_check() do the dirty work.
388 #define rcu_dereference_bh(p) \
389 rcu_dereference_check(p, rcu_read_lock_bh_held())
392 * rcu_dereference_sched - fetch RCU-protected pointer, checking for RCU-sched
394 * Makes rcu_dereference_check() do the dirty work.
396 #define rcu_dereference_sched(p) \
397 rcu_dereference_check(p, rcu_read_lock_sched_held())
400 * rcu_assign_pointer - assign (publicize) a pointer to a newly
401 * initialized structure that will be dereferenced by RCU read-side
402 * critical sections. Returns the value assigned.
404 * Inserts memory barriers on architectures that require them
405 * (pretty much all of them other than x86), and also prevents
406 * the compiler from reordering the code that initializes the
407 * structure after the pointer assignment. More importantly, this
408 * call documents which pointers will be dereferenced by RCU read-side
412 #define rcu_assign_pointer(p, v) \
414 if (!__builtin_constant_p(v) || \
420 /* Infrastructure to implement the synchronize_() primitives. */
422 struct rcu_synchronize {
423 struct rcu_head head;
424 struct completion completion;
427 extern void wakeme_after_rcu(struct rcu_head *head);
430 * call_rcu - Queue an RCU callback for invocation after a grace period.
431 * @head: structure to be used for queueing the RCU updates.
432 * @func: actual update function to be invoked after the grace period
434 * The update function will be invoked some time after a full grace
435 * period elapses, in other words after all currently executing RCU
436 * read-side critical sections have completed. RCU read-side critical
437 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
440 extern void call_rcu(struct rcu_head *head,
441 void (*func)(struct rcu_head *head));
444 * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
445 * @head: structure to be used for queueing the RCU updates.
446 * @func: actual update function to be invoked after the grace period
448 * The update function will be invoked some time after a full grace
449 * period elapses, in other words after all currently executing RCU
450 * read-side critical sections have completed. call_rcu_bh() assumes
451 * that the read-side critical sections end on completion of a softirq
452 * handler. This means that read-side critical sections in process
453 * context must not be interrupted by softirqs. This interface is to be
454 * used when most of the read-side critical sections are in softirq context.
455 * RCU read-side critical sections are delimited by :
456 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
458 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
459 * These may be nested.
461 extern void call_rcu_bh(struct rcu_head *head,
462 void (*func)(struct rcu_head *head));
464 #endif /* __LINUX_RCUPDATE_H */