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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
Paul E. McKenneya71fca52009-09-18 10:28:19 -07002 * Read-Copy Update mechanism for mutual exclusion
Linus Torvalds1da177e2005-04-16 15:20:36 -07003 *
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.
8 *
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.
13 *
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.
17 *
Paul E. McKenney01c1c662008-01-25 21:08:24 +010018 * Copyright IBM Corporation, 2001
Linus Torvalds1da177e2005-04-16 15:20:36 -070019 *
20 * Author: Dipankar Sarma <dipankar@in.ibm.com>
Paul E. McKenneya71fca52009-09-18 10:28:19 -070021 *
Josh Triplett595182b2006-10-04 02:17:21 -070022 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
Linus Torvalds1da177e2005-04-16 15:20:36 -070023 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
24 * Papers:
25 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
26 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
27 *
28 * For detailed explanation of Read-Copy Update mechanism see -
Paul E. McKenneya71fca52009-09-18 10:28:19 -070029 * http://lse.sourceforge.net/locking/rcupdate.html
Linus Torvalds1da177e2005-04-16 15:20:36 -070030 *
31 */
32
33#ifndef __LINUX_RCUPDATE_H
34#define __LINUX_RCUPDATE_H
35
Linus Torvalds1da177e2005-04-16 15:20:36 -070036#include <linux/cache.h>
37#include <linux/spinlock.h>
38#include <linux/threads.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070039#include <linux/cpumask.h>
40#include <linux/seqlock.h>
Peter Zijlstra851a67b2007-10-11 22:11:12 +020041#include <linux/lockdep.h>
Paul E. McKenney4446a362008-05-12 21:21:05 +020042#include <linux/completion.h>
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -040043#include <linux/debugobjects.h>
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -070044#include <linux/compiler.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070045
Dave Younge5ab6772010-03-10 15:24:05 -080046#ifdef CONFIG_RCU_TORTURE_TEST
47extern int rcutorture_runnable; /* for sysctl */
48#endif /* #ifdef CONFIG_RCU_TORTURE_TEST */
49
Paul E. McKenney4a298652011-04-03 21:33:51 -070050#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
51extern void rcutorture_record_test_transition(void);
52extern void rcutorture_record_progress(unsigned long vernum);
53#else
54static inline void rcutorture_record_test_transition(void)
55{
56}
57static inline void rcutorture_record_progress(unsigned long vernum)
58{
59}
60#endif
61
Tejun Heoe27fc962010-11-22 21:36:11 -080062#define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b))
63#define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b))
Paul E. McKenneya3dc3fb2010-08-13 16:16:25 -070064#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))
65#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b))
66
Linus Torvalds1da177e2005-04-16 15:20:36 -070067/**
68 * struct rcu_head - callback structure for use with RCU
69 * @next: next update requests in a list
70 * @func: actual update function to call after the grace period.
71 */
72struct rcu_head {
73 struct rcu_head *next;
74 void (*func)(struct rcu_head *head);
75};
76
Paul E. McKenney03b042b2009-06-25 09:08:16 -070077/* Exported common interfaces */
Paul E. McKenney7b0b7592010-08-17 14:18:46 -070078extern void call_rcu_sched(struct rcu_head *head,
79 void (*func)(struct rcu_head *rcu));
80extern void synchronize_sched(void);
Paul E. McKenney03b042b2009-06-25 09:08:16 -070081extern void rcu_barrier_bh(void);
82extern void rcu_barrier_sched(void);
Paul E. McKenney03b042b2009-06-25 09:08:16 -070083
Paul E. McKenney7b0b7592010-08-17 14:18:46 -070084static inline void __rcu_read_lock_bh(void)
85{
86 local_bh_disable();
87}
88
89static inline void __rcu_read_unlock_bh(void)
90{
91 local_bh_enable();
92}
Paul E. McKenneya6826042009-02-25 18:03:42 -080093
Paul E. McKenneya3dc3fb2010-08-13 16:16:25 -070094#ifdef CONFIG_PREEMPT_RCU
95
Paul E. McKenney7b0b7592010-08-17 14:18:46 -070096extern void __rcu_read_lock(void);
97extern void __rcu_read_unlock(void);
98void synchronize_rcu(void);
99
Paul E. McKenneya3dc3fb2010-08-13 16:16:25 -0700100/*
101 * Defined as a macro as it is a very low level header included from
102 * areas that don't even know about current. This gives the rcu_read_lock()
103 * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
104 * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
105 */
106#define rcu_preempt_depth() (current->rcu_read_lock_nesting)
107
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700108#else /* #ifdef CONFIG_PREEMPT_RCU */
109
110static inline void __rcu_read_lock(void)
111{
112 preempt_disable();
113}
114
115static inline void __rcu_read_unlock(void)
116{
117 preempt_enable();
118}
119
120static inline void synchronize_rcu(void)
121{
122 synchronize_sched();
123}
124
125static inline int rcu_preempt_depth(void)
126{
127 return 0;
128}
129
130#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
131
132/* Internal to kernel */
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700133extern void rcu_sched_qs(int cpu);
134extern void rcu_bh_qs(int cpu);
135extern void rcu_check_callbacks(int cpu, int user);
136struct notifier_block;
137
138#ifdef CONFIG_NO_HZ
139
140extern void rcu_enter_nohz(void);
141extern void rcu_exit_nohz(void);
142
143#else /* #ifdef CONFIG_NO_HZ */
144
145static inline void rcu_enter_nohz(void)
146{
147}
148
149static inline void rcu_exit_nohz(void)
150{
151}
152
153#endif /* #else #ifdef CONFIG_NO_HZ */
Paul E. McKenneya3dc3fb2010-08-13 16:16:25 -0700154
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700155#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
Paul E. McKenney64db4cf2008-12-18 21:55:32 +0100156#include <linux/rcutree.h>
Paul E. McKenneya57eb942010-06-29 16:49:16 -0700157#elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU)
Paul E. McKenney9b1d82f2009-10-25 19:03:50 -0700158#include <linux/rcutiny.h>
Paul E. McKenney64db4cf2008-12-18 21:55:32 +0100159#else
160#error "Unknown RCU implementation specified to kernel configuration"
Paul E. McKenney6b3ef482009-08-22 13:56:53 -0700161#endif
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100162
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400163/*
164 * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic
165 * initialization and destruction of rcu_head on the stack. rcu_head structures
166 * allocated dynamically in the heap or defined statically don't need any
167 * initialization.
168 */
169#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
170extern void init_rcu_head_on_stack(struct rcu_head *head);
171extern void destroy_rcu_head_on_stack(struct rcu_head *head);
172#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
Mathieu Desnoyers43760302010-04-17 08:48:39 -0400173static inline void init_rcu_head_on_stack(struct rcu_head *head)
174{
175}
176
177static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
178{
179}
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400180#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
Mathieu Desnoyers43760302010-04-17 08:48:39 -0400181
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700182#ifdef CONFIG_DEBUG_LOCK_ALLOC
Paul E. McKenney632ee202010-02-22 17:04:45 -0800183
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700184extern struct lockdep_map rcu_lock_map;
Paul E. McKenney632ee202010-02-22 17:04:45 -0800185# define rcu_read_acquire() \
186 lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700187# define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_)
Paul E. McKenney632ee202010-02-22 17:04:45 -0800188
189extern struct lockdep_map rcu_bh_lock_map;
190# define rcu_read_acquire_bh() \
191 lock_acquire(&rcu_bh_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
192# define rcu_read_release_bh() lock_release(&rcu_bh_lock_map, 1, _THIS_IP_)
193
194extern struct lockdep_map rcu_sched_lock_map;
195# define rcu_read_acquire_sched() \
196 lock_acquire(&rcu_sched_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
197# define rcu_read_release_sched() \
198 lock_release(&rcu_sched_lock_map, 1, _THIS_IP_)
199
Paul E. McKenneybc293d62010-04-15 12:50:39 -0700200extern int debug_lockdep_rcu_enabled(void);
Paul E. McKenney54dbf962010-03-03 07:46:57 -0800201
Paul E. McKenney632ee202010-02-22 17:04:45 -0800202/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700203 * rcu_read_lock_held() - might we be in RCU read-side critical section?
Paul E. McKenney632ee202010-02-22 17:04:45 -0800204 *
Paul E. McKenneyd20200b2010-03-30 10:52:21 -0700205 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
206 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
Paul E. McKenney632ee202010-02-22 17:04:45 -0800207 * this assumes we are in an RCU read-side critical section unless it can
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700208 * prove otherwise. This is useful for debug checks in functions that
209 * require that they be called within an RCU read-side critical section.
Paul E. McKenney54dbf962010-03-03 07:46:57 -0800210 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700211 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
Paul E. McKenney32c141a2010-03-30 10:59:28 -0700212 * and while lockdep is disabled.
Paul E. McKenney632ee202010-02-22 17:04:45 -0800213 */
214static inline int rcu_read_lock_held(void)
215{
Paul E. McKenney54dbf962010-03-03 07:46:57 -0800216 if (!debug_lockdep_rcu_enabled())
217 return 1;
218 return lock_is_held(&rcu_lock_map);
Paul E. McKenney632ee202010-02-22 17:04:45 -0800219}
220
Paul E. McKenneye3818b82010-03-15 17:03:43 -0700221/*
222 * rcu_read_lock_bh_held() is defined out of line to avoid #include-file
223 * hell.
Paul E. McKenney632ee202010-02-22 17:04:45 -0800224 */
Paul E. McKenneye3818b82010-03-15 17:03:43 -0700225extern int rcu_read_lock_bh_held(void);
Paul E. McKenney632ee202010-02-22 17:04:45 -0800226
227/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700228 * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
Paul E. McKenney632ee202010-02-22 17:04:45 -0800229 *
Paul E. McKenneyd20200b2010-03-30 10:52:21 -0700230 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
231 * RCU-sched read-side critical section. In absence of
232 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
233 * critical section unless it can prove otherwise. Note that disabling
234 * of preemption (including disabling irqs) counts as an RCU-sched
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700235 * read-side critical section. This is useful for debug checks in functions
236 * that required that they be called within an RCU-sched read-side
237 * critical section.
Paul E. McKenney54dbf962010-03-03 07:46:57 -0800238 *
Paul E. McKenney32c141a2010-03-30 10:59:28 -0700239 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
240 * and while lockdep is disabled.
Paul E. McKenney632ee202010-02-22 17:04:45 -0800241 */
Paul E. McKenneye6033e32010-03-03 17:50:16 -0800242#ifdef CONFIG_PREEMPT
Paul E. McKenney632ee202010-02-22 17:04:45 -0800243static inline int rcu_read_lock_sched_held(void)
244{
245 int lockdep_opinion = 0;
246
Paul E. McKenney54dbf962010-03-03 07:46:57 -0800247 if (!debug_lockdep_rcu_enabled())
248 return 1;
Paul E. McKenney632ee202010-02-22 17:04:45 -0800249 if (debug_locks)
250 lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
Lai Jiangshan0cff8102010-03-18 12:25:33 -0700251 return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
Paul E. McKenney632ee202010-02-22 17:04:45 -0800252}
Paul E. McKenneye6033e32010-03-03 17:50:16 -0800253#else /* #ifdef CONFIG_PREEMPT */
254static inline int rcu_read_lock_sched_held(void)
255{
256 return 1;
257}
258#endif /* #else #ifdef CONFIG_PREEMPT */
Paul E. McKenney632ee202010-02-22 17:04:45 -0800259
260#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
261
262# define rcu_read_acquire() do { } while (0)
263# define rcu_read_release() do { } while (0)
264# define rcu_read_acquire_bh() do { } while (0)
265# define rcu_read_release_bh() do { } while (0)
266# define rcu_read_acquire_sched() do { } while (0)
267# define rcu_read_release_sched() do { } while (0)
268
269static inline int rcu_read_lock_held(void)
270{
271 return 1;
272}
273
274static inline int rcu_read_lock_bh_held(void)
275{
276 return 1;
277}
278
Paul E. McKenneye6033e32010-03-03 17:50:16 -0800279#ifdef CONFIG_PREEMPT
Paul E. McKenney632ee202010-02-22 17:04:45 -0800280static inline int rcu_read_lock_sched_held(void)
281{
Paul E. McKenneybbad9372010-04-02 16:17:17 -0700282 return preempt_count() != 0 || irqs_disabled();
Paul E. McKenney632ee202010-02-22 17:04:45 -0800283}
Paul E. McKenneye6033e32010-03-03 17:50:16 -0800284#else /* #ifdef CONFIG_PREEMPT */
285static inline int rcu_read_lock_sched_held(void)
286{
287 return 1;
288}
289#endif /* #else #ifdef CONFIG_PREEMPT */
Paul E. McKenney632ee202010-02-22 17:04:45 -0800290
291#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
292
293#ifdef CONFIG_PROVE_RCU
294
Paul E. McKenneyee84b822010-05-06 09:28:41 -0700295extern int rcu_my_thread_group_empty(void);
296
Tetsuo Handa4221a992010-06-26 01:08:19 +0900297/**
298 * rcu_lockdep_assert - emit lockdep splat if specified condition not met
299 * @c: condition to check
300 */
301#define rcu_lockdep_assert(c) \
Lai Jiangshan2b3fc352010-04-20 16:23:07 +0800302 do { \
303 static bool __warned; \
304 if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
305 __warned = true; \
306 lockdep_rcu_dereference(__FILE__, __LINE__); \
307 } \
308 } while (0)
309
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700310#else /* #ifdef CONFIG_PROVE_RCU */
311
Tetsuo Handa4221a992010-06-26 01:08:19 +0900312#define rcu_lockdep_assert(c) do { } while (0)
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700313
314#endif /* #else #ifdef CONFIG_PROVE_RCU */
315
316/*
317 * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
318 * and rcu_assign_pointer(). Some of these could be folded into their
319 * callers, but they are left separate in order to ease introduction of
320 * multiple flavors of pointers to match the multiple flavors of RCU
321 * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in
322 * the future.
323 */
Paul E. McKenney53ecfba2010-09-13 17:24:21 -0700324
325#ifdef __CHECKER__
326#define rcu_dereference_sparse(p, space) \
327 ((void)(((typeof(*p) space *)p) == p))
328#else /* #ifdef __CHECKER__ */
329#define rcu_dereference_sparse(p, space)
330#endif /* #else #ifdef __CHECKER__ */
331
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700332#define __rcu_access_pointer(p, space) \
333 ({ \
334 typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
Paul E. McKenney53ecfba2010-09-13 17:24:21 -0700335 rcu_dereference_sparse(p, space); \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700336 ((typeof(*p) __force __kernel *)(_________p1)); \
337 })
338#define __rcu_dereference_check(p, c, space) \
339 ({ \
340 typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
Tetsuo Handa4221a992010-06-26 01:08:19 +0900341 rcu_lockdep_assert(c); \
Paul E. McKenney53ecfba2010-09-13 17:24:21 -0700342 rcu_dereference_sparse(p, space); \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700343 smp_read_barrier_depends(); \
344 ((typeof(*p) __force __kernel *)(_________p1)); \
345 })
346#define __rcu_dereference_protected(p, c, space) \
347 ({ \
Tetsuo Handa4221a992010-06-26 01:08:19 +0900348 rcu_lockdep_assert(c); \
Paul E. McKenney53ecfba2010-09-13 17:24:21 -0700349 rcu_dereference_sparse(p, space); \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700350 ((typeof(*p) __force __kernel *)(p)); \
351 })
352
Paul E. McKenneya4dd9922011-04-01 07:15:14 -0700353#define __rcu_access_index(p, space) \
354 ({ \
355 typeof(p) _________p1 = ACCESS_ONCE(p); \
356 rcu_dereference_sparse(p, space); \
357 (_________p1); \
358 })
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700359#define __rcu_dereference_index_check(p, c) \
360 ({ \
361 typeof(p) _________p1 = ACCESS_ONCE(p); \
Tetsuo Handa4221a992010-06-26 01:08:19 +0900362 rcu_lockdep_assert(c); \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700363 smp_read_barrier_depends(); \
364 (_________p1); \
365 })
366#define __rcu_assign_pointer(p, v, space) \
367 ({ \
368 if (!__builtin_constant_p(v) || \
369 ((v) != NULL)) \
370 smp_wmb(); \
371 (p) = (typeof(*v) __force space *)(v); \
372 })
373
374
Paul E. McKenney632ee202010-02-22 17:04:45 -0800375/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700376 * rcu_access_pointer() - fetch RCU pointer with no dereferencing
377 * @p: The pointer to read
378 *
379 * Return the value of the specified RCU-protected pointer, but omit the
380 * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful
381 * when the value of this pointer is accessed, but the pointer is not
382 * dereferenced, for example, when testing an RCU-protected pointer against
383 * NULL. Although rcu_access_pointer() may also be used in cases where
384 * update-side locks prevent the value of the pointer from changing, you
385 * should instead use rcu_dereference_protected() for this use case.
386 */
387#define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
388
389/**
390 * rcu_dereference_check() - rcu_dereference with debug checking
David Howellsc08c68d2010-04-09 15:39:11 -0700391 * @p: The pointer to read, prior to dereferencing
392 * @c: The conditions under which the dereference will take place
Paul E. McKenney632ee202010-02-22 17:04:45 -0800393 *
David Howellsc08c68d2010-04-09 15:39:11 -0700394 * Do an rcu_dereference(), but check that the conditions under which the
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700395 * dereference will take place are correct. Typically the conditions
396 * indicate the various locking conditions that should be held at that
397 * point. The check should return true if the conditions are satisfied.
398 * An implicit check for being in an RCU read-side critical section
399 * (rcu_read_lock()) is included.
David Howellsc08c68d2010-04-09 15:39:11 -0700400 *
401 * For example:
402 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700403 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
David Howellsc08c68d2010-04-09 15:39:11 -0700404 *
405 * could be used to indicate to lockdep that foo->bar may only be dereferenced
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700406 * if either rcu_read_lock() is held, or that the lock required to replace
David Howellsc08c68d2010-04-09 15:39:11 -0700407 * the bar struct at foo->bar is held.
408 *
409 * Note that the list of conditions may also include indications of when a lock
410 * need not be held, for example during initialisation or destruction of the
411 * target struct:
412 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700413 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
David Howellsc08c68d2010-04-09 15:39:11 -0700414 * atomic_read(&foo->usage) == 0);
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700415 *
416 * Inserts memory barriers on architectures that require them
417 * (currently only the Alpha), prevents the compiler from refetching
418 * (and from merging fetches), and, more importantly, documents exactly
419 * which pointers are protected by RCU and checks that the pointer is
420 * annotated as __rcu.
Paul E. McKenney632ee202010-02-22 17:04:45 -0800421 */
422#define rcu_dereference_check(p, c) \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700423 __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)
Paul E. McKenney632ee202010-02-22 17:04:45 -0800424
Paul E. McKenneyb62730b2010-04-09 15:39:10 -0700425/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700426 * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
427 * @p: The pointer to read, prior to dereferencing
428 * @c: The conditions under which the dereference will take place
429 *
430 * This is the RCU-bh counterpart to rcu_dereference_check().
431 */
432#define rcu_dereference_bh_check(p, c) \
433 __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu)
434
435/**
436 * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
437 * @p: The pointer to read, prior to dereferencing
438 * @c: The conditions under which the dereference will take place
439 *
440 * This is the RCU-sched counterpart to rcu_dereference_check().
441 */
442#define rcu_dereference_sched_check(p, c) \
443 __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \
444 __rcu)
445
446#define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/
447
448/**
Paul E. McKenneya4dd9922011-04-01 07:15:14 -0700449 * rcu_access_index() - fetch RCU index with no dereferencing
450 * @p: The index to read
451 *
452 * Return the value of the specified RCU-protected index, but omit the
453 * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful
454 * when the value of this index is accessed, but the index is not
455 * dereferenced, for example, when testing an RCU-protected index against
456 * -1. Although rcu_access_index() may also be used in cases where
457 * update-side locks prevent the value of the index from changing, you
458 * should instead use rcu_dereference_index_protected() for this use case.
459 */
460#define rcu_access_index(p) __rcu_access_index((p), __rcu)
461
462/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700463 * rcu_dereference_index_check() - rcu_dereference for indices with debug checking
464 * @p: The pointer to read, prior to dereferencing
465 * @c: The conditions under which the dereference will take place
466 *
467 * Similar to rcu_dereference_check(), but omits the sparse checking.
468 * This allows rcu_dereference_index_check() to be used on integers,
469 * which can then be used as array indices. Attempting to use
470 * rcu_dereference_check() on an integer will give compiler warnings
471 * because the sparse address-space mechanism relies on dereferencing
472 * the RCU-protected pointer. Dereferencing integers is not something
473 * that even gcc will put up with.
474 *
475 * Note that this function does not implicitly check for RCU read-side
476 * critical sections. If this function gains lots of uses, it might
477 * make sense to provide versions for each flavor of RCU, but it does
478 * not make sense as of early 2010.
479 */
480#define rcu_dereference_index_check(p, c) \
481 __rcu_dereference_index_check((p), (c))
482
483/**
484 * rcu_dereference_protected() - fetch RCU pointer when updates prevented
485 * @p: The pointer to read, prior to dereferencing
486 * @c: The conditions under which the dereference will take place
Paul E. McKenneyb62730b2010-04-09 15:39:10 -0700487 *
488 * Return the value of the specified RCU-protected pointer, but omit
489 * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This
490 * is useful in cases where update-side locks prevent the value of the
491 * pointer from changing. Please note that this primitive does -not-
492 * prevent the compiler from repeating this reference or combining it
493 * with other references, so it should not be used without protection
494 * of appropriate locks.
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700495 *
496 * This function is only for update-side use. Using this function
497 * when protected only by rcu_read_lock() will result in infrequent
498 * but very ugly failures.
Paul E. McKenneyb62730b2010-04-09 15:39:10 -0700499 */
500#define rcu_dereference_protected(p, c) \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700501 __rcu_dereference_protected((p), (c), __rcu)
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700502
Linus Torvalds1da177e2005-04-16 15:20:36 -0700503/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700504 * rcu_dereference_bh_protected() - fetch RCU-bh pointer when updates prevented
505 * @p: The pointer to read, prior to dereferencing
506 * @c: The conditions under which the dereference will take place
Paul E. McKenneyb62730b2010-04-09 15:39:10 -0700507 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700508 * This is the RCU-bh counterpart to rcu_dereference_protected().
Paul E. McKenneyb62730b2010-04-09 15:39:10 -0700509 */
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700510#define rcu_dereference_bh_protected(p, c) \
511 __rcu_dereference_protected((p), (c), __rcu)
Paul E. McKenneyb62730b2010-04-09 15:39:10 -0700512
513/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700514 * rcu_dereference_sched_protected() - fetch RCU-sched pointer when updates prevented
515 * @p: The pointer to read, prior to dereferencing
516 * @c: The conditions under which the dereference will take place
517 *
518 * This is the RCU-sched counterpart to rcu_dereference_protected().
519 */
520#define rcu_dereference_sched_protected(p, c) \
521 __rcu_dereference_protected((p), (c), __rcu)
522
523
524/**
525 * rcu_dereference() - fetch RCU-protected pointer for dereferencing
526 * @p: The pointer to read, prior to dereferencing
527 *
528 * This is a simple wrapper around rcu_dereference_check().
529 */
530#define rcu_dereference(p) rcu_dereference_check(p, 0)
531
532/**
533 * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
534 * @p: The pointer to read, prior to dereferencing
535 *
536 * Makes rcu_dereference_check() do the dirty work.
537 */
538#define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
539
540/**
541 * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
542 * @p: The pointer to read, prior to dereferencing
543 *
544 * Makes rcu_dereference_check() do the dirty work.
545 */
546#define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
547
548/**
549 * rcu_read_lock() - mark the beginning of an RCU read-side critical section
Linus Torvalds1da177e2005-04-16 15:20:36 -0700550 *
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700551 * When synchronize_rcu() is invoked on one CPU while other CPUs
Linus Torvalds1da177e2005-04-16 15:20:36 -0700552 * are within RCU read-side critical sections, then the
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700553 * synchronize_rcu() is guaranteed to block until after all the other
Linus Torvalds1da177e2005-04-16 15:20:36 -0700554 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
555 * on one CPU while other CPUs are within RCU read-side critical
556 * sections, invocation of the corresponding RCU callback is deferred
557 * until after the all the other CPUs exit their critical sections.
558 *
559 * Note, however, that RCU callbacks are permitted to run concurrently
Paul E. McKenney77d84852010-07-08 17:38:59 -0700560 * with new RCU read-side critical sections. One way that this can happen
Linus Torvalds1da177e2005-04-16 15:20:36 -0700561 * is via the following sequence of events: (1) CPU 0 enters an RCU
562 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
563 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
564 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
565 * callback is invoked. This is legal, because the RCU read-side critical
566 * section that was running concurrently with the call_rcu() (and which
567 * therefore might be referencing something that the corresponding RCU
568 * callback would free up) has completed before the corresponding
569 * RCU callback is invoked.
570 *
571 * RCU read-side critical sections may be nested. Any deferred actions
572 * will be deferred until the outermost RCU read-side critical section
573 * completes.
574 *
Paul E. McKenney9079fd72010-08-07 21:59:54 -0700575 * You can avoid reading and understanding the next paragraph by
576 * following this rule: don't put anything in an rcu_read_lock() RCU
577 * read-side critical section that would block in a !PREEMPT kernel.
578 * But if you want the full story, read on!
579 *
580 * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it
581 * is illegal to block while in an RCU read-side critical section. In
582 * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU)
583 * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may
584 * be preempted, but explicit blocking is illegal. Finally, in preemptible
585 * RCU implementations in real-time (CONFIG_PREEMPT_RT) kernel builds,
586 * RCU read-side critical sections may be preempted and they may also
587 * block, but only when acquiring spinlocks that are subject to priority
588 * inheritance.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700589 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700590static inline void rcu_read_lock(void)
591{
592 __rcu_read_lock();
593 __acquire(RCU);
594 rcu_read_acquire();
595}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700596
Linus Torvalds1da177e2005-04-16 15:20:36 -0700597/*
598 * So where is rcu_write_lock()? It does not exist, as there is no
599 * way for writers to lock out RCU readers. This is a feature, not
600 * a bug -- this property is what provides RCU's performance benefits.
601 * Of course, writers must coordinate with each other. The normal
602 * spinlock primitives work well for this, but any other technique may be
603 * used as well. RCU does not care how the writers keep out of each
604 * others' way, as long as they do so.
605 */
Paul E. McKenney3d76c082009-09-28 07:46:32 -0700606
607/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700608 * rcu_read_unlock() - marks the end of an RCU read-side critical section.
Paul E. McKenney3d76c082009-09-28 07:46:32 -0700609 *
610 * See rcu_read_lock() for more information.
611 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700612static inline void rcu_read_unlock(void)
613{
614 rcu_read_release();
615 __release(RCU);
616 __rcu_read_unlock();
617}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700618
619/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700620 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
Linus Torvalds1da177e2005-04-16 15:20:36 -0700621 *
622 * This is equivalent of rcu_read_lock(), but to be used when updates
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700623 * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since
624 * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a
625 * softirq handler to be a quiescent state, a process in RCU read-side
626 * critical section must be protected by disabling softirqs. Read-side
627 * critical sections in interrupt context can use just rcu_read_lock(),
628 * though this should at least be commented to avoid confusing people
629 * reading the code.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700630 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700631static inline void rcu_read_lock_bh(void)
632{
633 __rcu_read_lock_bh();
634 __acquire(RCU_BH);
Paul E. McKenney632ee202010-02-22 17:04:45 -0800635 rcu_read_acquire_bh();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700636}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700637
638/*
639 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
640 *
641 * See rcu_read_lock_bh() for more information.
642 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700643static inline void rcu_read_unlock_bh(void)
644{
Paul E. McKenney632ee202010-02-22 17:04:45 -0800645 rcu_read_release_bh();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700646 __release(RCU_BH);
647 __rcu_read_unlock_bh();
648}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700649
650/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700651 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400652 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700653 * This is equivalent of rcu_read_lock(), but to be used when updates
654 * are being done using call_rcu_sched() or synchronize_rcu_sched().
655 * Read-side critical sections can also be introduced by anything that
656 * disables preemption, including local_irq_disable() and friends.
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400657 */
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700658static inline void rcu_read_lock_sched(void)
659{
660 preempt_disable();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700661 __acquire(RCU_SCHED);
Paul E. McKenney632ee202010-02-22 17:04:45 -0800662 rcu_read_acquire_sched();
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700663}
Paul E. McKenney1eba8f82009-09-23 09:50:42 -0700664
665/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
Paul E. McKenney7c614d62009-08-24 09:42:00 -0700666static inline notrace void rcu_read_lock_sched_notrace(void)
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700667{
668 preempt_disable_notrace();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700669 __acquire(RCU_SCHED);
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700670}
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400671
672/*
673 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
674 *
675 * See rcu_read_lock_sched for more information.
676 */
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700677static inline void rcu_read_unlock_sched(void)
678{
Paul E. McKenney632ee202010-02-22 17:04:45 -0800679 rcu_read_release_sched();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700680 __release(RCU_SCHED);
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700681 preempt_enable();
682}
Paul E. McKenney1eba8f82009-09-23 09:50:42 -0700683
684/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
Paul E. McKenney7c614d62009-08-24 09:42:00 -0700685static inline notrace void rcu_read_unlock_sched_notrace(void)
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700686{
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700687 __release(RCU_SCHED);
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700688 preempt_enable_notrace();
689}
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400690
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400691/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700692 * rcu_assign_pointer() - assign to RCU-protected pointer
693 * @p: pointer to assign to
694 * @v: value to assign (publish)
Paul E. McKenneyc26d34a2010-02-22 17:04:46 -0800695 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700696 * Assigns the specified value to the specified RCU-protected
697 * pointer, ensuring that any concurrent RCU readers will see
698 * any prior initialization. Returns the value assigned.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700699 *
700 * Inserts memory barriers on architectures that require them
701 * (pretty much all of them other than x86), and also prevents
702 * the compiler from reordering the code that initializes the
703 * structure after the pointer assignment. More importantly, this
704 * call documents which pointers will be dereferenced by RCU read-side
705 * code.
706 */
Paul E. McKenneyd99c4f62008-02-06 01:37:25 -0800707#define rcu_assign_pointer(p, v) \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700708 __rcu_assign_pointer((p), (v), __rcu)
709
710/**
711 * RCU_INIT_POINTER() - initialize an RCU protected pointer
712 *
713 * Initialize an RCU-protected pointer in such a way to avoid RCU-lockdep
714 * splats.
715 */
716#define RCU_INIT_POINTER(p, v) \
717 p = (typeof(*v) __force __rcu *)(v)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700718
Paul E. McKenney4446a362008-05-12 21:21:05 +0200719/* Infrastructure to implement the synchronize_() primitives. */
720
721struct rcu_synchronize {
722 struct rcu_head head;
723 struct completion completion;
724};
725
726extern void wakeme_after_rcu(struct rcu_head *head);
727
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700728#ifdef CONFIG_PREEMPT_RCU
729
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700730/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700731 * call_rcu() - Queue an RCU callback for invocation after a grace period.
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100732 * @head: structure to be used for queueing the RCU updates.
Paul E. McKenney77d84852010-07-08 17:38:59 -0700733 * @func: actual callback function to be invoked after the grace period
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100734 *
Paul E. McKenney77d84852010-07-08 17:38:59 -0700735 * The callback function will be invoked some time after a full grace
736 * period elapses, in other words after all pre-existing RCU read-side
737 * critical sections have completed. However, the callback function
738 * might well execute concurrently with RCU read-side critical sections
739 * that started after call_rcu() was invoked. RCU read-side critical
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100740 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
741 * and may be nested.
742 */
743extern void call_rcu(struct rcu_head *head,
744 void (*func)(struct rcu_head *head));
Linus Torvalds1da177e2005-04-16 15:20:36 -0700745
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700746#else /* #ifdef CONFIG_PREEMPT_RCU */
747
748/* In classic RCU, call_rcu() is just call_rcu_sched(). */
749#define call_rcu call_rcu_sched
750
751#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
752
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100753/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700754 * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100755 * @head: structure to be used for queueing the RCU updates.
Paul E. McKenney77d84852010-07-08 17:38:59 -0700756 * @func: actual callback function to be invoked after the grace period
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100757 *
Paul E. McKenney77d84852010-07-08 17:38:59 -0700758 * The callback function will be invoked some time after a full grace
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100759 * period elapses, in other words after all currently executing RCU
760 * read-side critical sections have completed. call_rcu_bh() assumes
761 * that the read-side critical sections end on completion of a softirq
762 * handler. This means that read-side critical sections in process
763 * context must not be interrupted by softirqs. This interface is to be
764 * used when most of the read-side critical sections are in softirq context.
765 * RCU read-side critical sections are delimited by :
766 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
767 * OR
768 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
769 * These may be nested.
770 */
771extern void call_rcu_bh(struct rcu_head *head,
772 void (*func)(struct rcu_head *head));
773
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400774/*
775 * debug_rcu_head_queue()/debug_rcu_head_unqueue() are used internally
776 * by call_rcu() and rcu callback execution, and are therefore not part of the
777 * RCU API. Leaving in rcupdate.h because they are used by all RCU flavors.
778 */
779
780#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
781# define STATE_RCU_HEAD_READY 0
782# define STATE_RCU_HEAD_QUEUED 1
783
784extern struct debug_obj_descr rcuhead_debug_descr;
785
786static inline void debug_rcu_head_queue(struct rcu_head *head)
787{
Paul E. McKenneyb0c9d7f2011-03-29 12:56:56 -0700788 WARN_ON_ONCE((unsigned long)head & 0x3);
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400789 debug_object_activate(head, &rcuhead_debug_descr);
790 debug_object_active_state(head, &rcuhead_debug_descr,
791 STATE_RCU_HEAD_READY,
792 STATE_RCU_HEAD_QUEUED);
793}
794
795static inline void debug_rcu_head_unqueue(struct rcu_head *head)
796{
797 debug_object_active_state(head, &rcuhead_debug_descr,
798 STATE_RCU_HEAD_QUEUED,
799 STATE_RCU_HEAD_READY);
800 debug_object_deactivate(head, &rcuhead_debug_descr);
801}
802#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
803static inline void debug_rcu_head_queue(struct rcu_head *head)
804{
805}
806
807static inline void debug_rcu_head_unqueue(struct rcu_head *head)
808{
809}
810#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
811
Lai Jiangshan9ab15442011-03-18 11:15:47 +0800812static __always_inline bool __is_kfree_rcu_offset(unsigned long offset)
813{
814 return offset < 4096;
815}
816
817static __always_inline
818void __kfree_rcu(struct rcu_head *head, unsigned long offset)
819{
820 typedef void (*rcu_callback)(struct rcu_head *);
821
822 BUILD_BUG_ON(!__builtin_constant_p(offset));
823
824 /* See the kfree_rcu() header comment. */
825 BUILD_BUG_ON(!__is_kfree_rcu_offset(offset));
826
827 call_rcu(head, (rcu_callback)offset);
828}
829
830extern void kfree(const void *);
831
832static inline void __rcu_reclaim(struct rcu_head *head)
833{
834 unsigned long offset = (unsigned long)head->func;
835
836 if (__is_kfree_rcu_offset(offset))
837 kfree((void *)head - offset);
838 else
839 head->func(head);
840}
841
842/**
843 * kfree_rcu() - kfree an object after a grace period.
844 * @ptr: pointer to kfree
845 * @rcu_head: the name of the struct rcu_head within the type of @ptr.
846 *
847 * Many rcu callbacks functions just call kfree() on the base structure.
848 * These functions are trivial, but their size adds up, and furthermore
849 * when they are used in a kernel module, that module must invoke the
850 * high-latency rcu_barrier() function at module-unload time.
851 *
852 * The kfree_rcu() function handles this issue. Rather than encoding a
853 * function address in the embedded rcu_head structure, kfree_rcu() instead
854 * encodes the offset of the rcu_head structure within the base structure.
855 * Because the functions are not allowed in the low-order 4096 bytes of
856 * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
857 * If the offset is larger than 4095 bytes, a compile-time error will
858 * be generated in __kfree_rcu(). If this error is triggered, you can
859 * either fall back to use of call_rcu() or rearrange the structure to
860 * position the rcu_head structure into the first 4096 bytes.
861 *
862 * Note that the allowable offset might decrease in the future, for example,
863 * to allow something like kmem_cache_free_rcu().
864 */
865#define kfree_rcu(ptr, rcu_head) \
866 __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
867
Linus Torvalds1da177e2005-04-16 15:20:36 -0700868#endif /* __LINUX_RCUPDATE_H */