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_)
105 * rcu_read_lock_held - might we be in RCU read-side critical section?
107 * If CONFIG_PROVE_LOCKING is selected and enabled, returns nonzero iff in
108 * an RCU read-side critical section. In absence of CONFIG_PROVE_LOCKING,
109 * this assumes we are in an RCU read-side critical section unless it can
112 static inline int rcu_read_lock_held(void)
115 return lock_is_held(&rcu_lock_map
);
120 * rcu_read_lock_bh_held - might we be in RCU-bh read-side critical section?
122 * If CONFIG_PROVE_LOCKING is selected and enabled, returns nonzero iff in
123 * an RCU-bh read-side critical section. In absence of CONFIG_PROVE_LOCKING,
124 * this assumes we are in an RCU-bh read-side critical section unless it can
127 static inline int rcu_read_lock_bh_held(void)
130 return lock_is_held(&rcu_bh_lock_map
);
135 * rcu_read_lock_sched_held - might we be in RCU-sched read-side critical section?
137 * If CONFIG_PROVE_LOCKING is selected and enabled, returns nonzero iff in an
138 * RCU-sched read-side critical section. In absence of CONFIG_PROVE_LOCKING,
139 * this assumes we are in an RCU-sched read-side critical section unless it
140 * can prove otherwise. Note that disabling of preemption (including
141 * disabling irqs) counts as an RCU-sched read-side critical section.
143 static inline int rcu_read_lock_sched_held(void)
145 int lockdep_opinion
= 0;
148 lockdep_opinion
= lock_is_held(&rcu_sched_lock_map
);
149 return lockdep_opinion
|| preempt_count() != 0 || !rcu_scheduler_active
;
152 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
154 # define rcu_read_acquire() do { } while (0)
155 # define rcu_read_release() do { } while (0)
156 # define rcu_read_acquire_bh() do { } while (0)
157 # define rcu_read_release_bh() do { } while (0)
158 # define rcu_read_acquire_sched() do { } while (0)
159 # define rcu_read_release_sched() do { } while (0)
161 static inline int rcu_read_lock_held(void)
166 static inline int rcu_read_lock_bh_held(void)
171 static inline int rcu_read_lock_sched_held(void)
173 return preempt_count() != 0 || !rcu_scheduler_active
;
176 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
178 #ifdef CONFIG_PROVE_RCU
181 * rcu_dereference_check - rcu_dereference with debug checking
183 * Do an rcu_dereference(), but check that the context is correct.
184 * For example, rcu_dereference_check(gp, rcu_read_lock_held()) to
185 * ensure that the rcu_dereference_check() executes within an RCU
186 * read-side critical section. It is also possible to check for
187 * locks being held, for example, by using lockdep_is_held().
189 #define rcu_dereference_check(p, c) \
191 if (debug_locks && !(c)) \
192 lockdep_rcu_dereference(__FILE__, __LINE__); \
193 rcu_dereference_raw(p); \
196 #else /* #ifdef CONFIG_PROVE_RCU */
198 #define rcu_dereference_check(p, c) rcu_dereference_raw(p)
200 #endif /* #else #ifdef CONFIG_PROVE_RCU */
203 * rcu_read_lock - mark the beginning of an RCU read-side critical section.
205 * When synchronize_rcu() is invoked on one CPU while other CPUs
206 * are within RCU read-side critical sections, then the
207 * synchronize_rcu() is guaranteed to block until after all the other
208 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
209 * on one CPU while other CPUs are within RCU read-side critical
210 * sections, invocation of the corresponding RCU callback is deferred
211 * until after the all the other CPUs exit their critical sections.
213 * Note, however, that RCU callbacks are permitted to run concurrently
214 * with RCU read-side critical sections. One way that this can happen
215 * is via the following sequence of events: (1) CPU 0 enters an RCU
216 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
217 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
218 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
219 * callback is invoked. This is legal, because the RCU read-side critical
220 * section that was running concurrently with the call_rcu() (and which
221 * therefore might be referencing something that the corresponding RCU
222 * callback would free up) has completed before the corresponding
223 * RCU callback is invoked.
225 * RCU read-side critical sections may be nested. Any deferred actions
226 * will be deferred until the outermost RCU read-side critical section
229 * It is illegal to block while in an RCU read-side critical section.
231 static inline void rcu_read_lock(void)
239 * So where is rcu_write_lock()? It does not exist, as there is no
240 * way for writers to lock out RCU readers. This is a feature, not
241 * a bug -- this property is what provides RCU's performance benefits.
242 * Of course, writers must coordinate with each other. The normal
243 * spinlock primitives work well for this, but any other technique may be
244 * used as well. RCU does not care how the writers keep out of each
245 * others' way, as long as they do so.
249 * rcu_read_unlock - marks the end of an RCU read-side critical section.
251 * See rcu_read_lock() for more information.
253 static inline void rcu_read_unlock(void)
261 * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
263 * This is equivalent of rcu_read_lock(), but to be used when updates
264 * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
265 * consider completion of a softirq handler to be a quiescent state,
266 * a process in RCU read-side critical section must be protected by
267 * disabling softirqs. Read-side critical sections in interrupt context
268 * can use just rcu_read_lock().
271 static inline void rcu_read_lock_bh(void)
273 __rcu_read_lock_bh();
275 rcu_read_acquire_bh();
279 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
281 * See rcu_read_lock_bh() for more information.
283 static inline void rcu_read_unlock_bh(void)
285 rcu_read_release_bh();
287 __rcu_read_unlock_bh();
291 * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
293 * Should be used with either
294 * - synchronize_sched()
296 * - call_rcu_sched() and rcu_barrier_sched()
297 * on the write-side to insure proper synchronization.
299 static inline void rcu_read_lock_sched(void)
302 __acquire(RCU_SCHED
);
303 rcu_read_acquire_sched();
306 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
307 static inline notrace
void rcu_read_lock_sched_notrace(void)
309 preempt_disable_notrace();
310 __acquire(RCU_SCHED
);
314 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
316 * See rcu_read_lock_sched for more information.
318 static inline void rcu_read_unlock_sched(void)
320 rcu_read_release_sched();
321 __release(RCU_SCHED
);
325 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
326 static inline notrace
void rcu_read_unlock_sched_notrace(void)
328 __release(RCU_SCHED
);
329 preempt_enable_notrace();
334 * rcu_dereference_raw - fetch an RCU-protected pointer
336 * The caller must be within some flavor of RCU read-side critical
337 * section, or must be otherwise preventing the pointer from changing,
338 * for example, by holding an appropriate lock. This pointer may later
339 * be safely dereferenced. It is the caller's responsibility to have
340 * done the right thing, as this primitive does no checking of any kind.
342 * Inserts memory barriers on architectures that require them
343 * (currently only the Alpha), and, more importantly, documents
344 * exactly which pointers are protected by RCU.
346 #define rcu_dereference_raw(p) ({ \
347 typeof(p) _________p1 = ACCESS_ONCE(p); \
348 smp_read_barrier_depends(); \
353 * rcu_dereference - fetch an RCU-protected pointer, checking for RCU
355 * Makes rcu_dereference_check() do the dirty work.
357 #define rcu_dereference(p) \
358 rcu_dereference_check(p, rcu_read_lock_held())
361 * rcu_dereference_bh - fetch an RCU-protected pointer, checking for RCU-bh
363 * Makes rcu_dereference_check() do the dirty work.
365 #define rcu_dereference_bh(p) \
366 rcu_dereference_check(p, rcu_read_lock_bh_held())
369 * rcu_dereference_sched - fetch RCU-protected pointer, checking for RCU-sched
371 * Makes rcu_dereference_check() do the dirty work.
373 #define rcu_dereference_sched(p) \
374 rcu_dereference_check(p, rcu_read_lock_sched_held())
377 * rcu_assign_pointer - assign (publicize) a pointer to a newly
378 * initialized structure that will be dereferenced by RCU read-side
379 * critical sections. Returns the value assigned.
381 * Inserts memory barriers on architectures that require them
382 * (pretty much all of them other than x86), and also prevents
383 * the compiler from reordering the code that initializes the
384 * structure after the pointer assignment. More importantly, this
385 * call documents which pointers will be dereferenced by RCU read-side
389 #define rcu_assign_pointer(p, v) \
391 if (!__builtin_constant_p(v) || \
397 /* Infrastructure to implement the synchronize_() primitives. */
399 struct rcu_synchronize
{
400 struct rcu_head head
;
401 struct completion completion
;
404 extern void wakeme_after_rcu(struct rcu_head
*head
);
407 * call_rcu - Queue an RCU callback for invocation after a grace period.
408 * @head: structure to be used for queueing the RCU updates.
409 * @func: actual update function to be invoked after the grace period
411 * The update function will be invoked some time after a full grace
412 * period elapses, in other words after all currently executing RCU
413 * read-side critical sections have completed. RCU read-side critical
414 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
417 extern void call_rcu(struct rcu_head
*head
,
418 void (*func
)(struct rcu_head
*head
));
421 * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
422 * @head: structure to be used for queueing the RCU updates.
423 * @func: actual update function to be invoked after the grace period
425 * The update function will be invoked some time after a full grace
426 * period elapses, in other words after all currently executing RCU
427 * read-side critical sections have completed. call_rcu_bh() assumes
428 * that the read-side critical sections end on completion of a softirq
429 * handler. This means that read-side critical sections in process
430 * context must not be interrupted by softirqs. This interface is to be
431 * used when most of the read-side critical sections are in softirq context.
432 * RCU read-side critical sections are delimited by :
433 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
435 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
436 * These may be nested.
438 extern void call_rcu_bh(struct rcu_head
*head
,
439 void (*func
)(struct rcu_head
*head
));
441 #endif /* __LINUX_RCUPDATE_H */