blob: 2cf4226ade7e60c11ed6d0a3d3f1a4f90496bc24 [file] [log] [blame]
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
Paul E. McKenney99098752011-05-31 21:03:55 -070036#include <linux/types.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070037#include <linux/cache.h>
38#include <linux/spinlock.h>
39#include <linux/threads.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070040#include <linux/cpumask.h>
41#include <linux/seqlock.h>
Peter Zijlstra851a67b2007-10-11 22:11:12 +020042#include <linux/lockdep.h>
Paul E. McKenney4446a362008-05-12 21:21:05 +020043#include <linux/completion.h>
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -040044#include <linux/debugobjects.h>
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -070045#include <linux/compiler.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070046
Dave Younge5ab6772010-03-10 15:24:05 -080047#ifdef CONFIG_RCU_TORTURE_TEST
48extern int rcutorture_runnable; /* for sysctl */
49#endif /* #ifdef CONFIG_RCU_TORTURE_TEST */
50
Paul E. McKenney4a298652011-04-03 21:33:51 -070051#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
52extern void rcutorture_record_test_transition(void);
53extern void rcutorture_record_progress(unsigned long vernum);
54#else
55static inline void rcutorture_record_test_transition(void)
56{
57}
58static inline void rcutorture_record_progress(unsigned long vernum)
59{
60}
61#endif
62
Tejun Heoe27fc962010-11-22 21:36:11 -080063#define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b))
64#define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b))
Paul E. McKenneya3dc3fb2010-08-13 16:16:25 -070065#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))
66#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b))
67
Paul E. McKenney03b042b2009-06-25 09:08:16 -070068/* Exported common interfaces */
Paul E. McKenney2c428182011-05-26 22:14:36 -070069
70#ifdef CONFIG_PREEMPT_RCU
71
72/**
73 * call_rcu() - Queue an RCU callback for invocation after a grace period.
74 * @head: structure to be used for queueing the RCU updates.
75 * @func: actual callback function to be invoked after the grace period
76 *
77 * The callback function will be invoked some time after a full grace
78 * period elapses, in other words after all pre-existing RCU read-side
79 * critical sections have completed. However, the callback function
80 * might well execute concurrently with RCU read-side critical sections
81 * that started after call_rcu() was invoked. RCU read-side critical
82 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
83 * and may be nested.
84 */
85extern void call_rcu(struct rcu_head *head,
86 void (*func)(struct rcu_head *head));
87
88#else /* #ifdef CONFIG_PREEMPT_RCU */
89
90/* In classic RCU, call_rcu() is just call_rcu_sched(). */
91#define call_rcu call_rcu_sched
92
93#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
94
95/**
96 * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
97 * @head: structure to be used for queueing the RCU updates.
98 * @func: actual callback function to be invoked after the grace period
99 *
100 * The callback function will be invoked some time after a full grace
101 * period elapses, in other words after all currently executing RCU
102 * read-side critical sections have completed. call_rcu_bh() assumes
103 * that the read-side critical sections end on completion of a softirq
104 * handler. This means that read-side critical sections in process
105 * context must not be interrupted by softirqs. This interface is to be
106 * used when most of the read-side critical sections are in softirq context.
107 * RCU read-side critical sections are delimited by :
108 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
109 * OR
110 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
111 * These may be nested.
112 */
113extern void call_rcu_bh(struct rcu_head *head,
114 void (*func)(struct rcu_head *head));
115
116/**
117 * call_rcu_sched() - Queue an RCU for invocation after sched grace period.
118 * @head: structure to be used for queueing the RCU updates.
119 * @func: actual callback function to be invoked after the grace period
120 *
121 * The callback function will be invoked some time after a full grace
122 * period elapses, in other words after all currently executing RCU
123 * read-side critical sections have completed. call_rcu_sched() assumes
124 * that the read-side critical sections end on enabling of preemption
125 * or on voluntary preemption.
126 * RCU read-side critical sections are delimited by :
127 * - rcu_read_lock_sched() and rcu_read_unlock_sched(),
128 * OR
129 * anything that disables preemption.
130 * These may be nested.
131 */
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700132extern void call_rcu_sched(struct rcu_head *head,
133 void (*func)(struct rcu_head *rcu));
Paul E. McKenney2c428182011-05-26 22:14:36 -0700134
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700135extern void synchronize_sched(void);
Paul E. McKenney03b042b2009-06-25 09:08:16 -0700136
Paul E. McKenneya3dc3fb2010-08-13 16:16:25 -0700137#ifdef CONFIG_PREEMPT_RCU
138
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700139extern void __rcu_read_lock(void);
140extern void __rcu_read_unlock(void);
141void synchronize_rcu(void);
142
Paul E. McKenneya3dc3fb2010-08-13 16:16:25 -0700143/*
144 * Defined as a macro as it is a very low level header included from
145 * areas that don't even know about current. This gives the rcu_read_lock()
146 * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
147 * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
148 */
149#define rcu_preempt_depth() (current->rcu_read_lock_nesting)
150
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700151#else /* #ifdef CONFIG_PREEMPT_RCU */
152
153static inline void __rcu_read_lock(void)
154{
155 preempt_disable();
156}
157
158static inline void __rcu_read_unlock(void)
159{
160 preempt_enable();
161}
162
163static inline void synchronize_rcu(void)
164{
165 synchronize_sched();
166}
167
168static inline int rcu_preempt_depth(void)
169{
170 return 0;
171}
172
173#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
174
175/* Internal to kernel */
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700176extern void rcu_sched_qs(int cpu);
177extern void rcu_bh_qs(int cpu);
178extern void rcu_check_callbacks(int cpu, int user);
179struct notifier_block;
180
181#ifdef CONFIG_NO_HZ
182
183extern void rcu_enter_nohz(void);
184extern void rcu_exit_nohz(void);
185
186#else /* #ifdef CONFIG_NO_HZ */
187
188static inline void rcu_enter_nohz(void)
189{
190}
191
192static inline void rcu_exit_nohz(void)
193{
194}
195
196#endif /* #else #ifdef CONFIG_NO_HZ */
Paul E. McKenneya3dc3fb2010-08-13 16:16:25 -0700197
Paul E. McKenney2c428182011-05-26 22:14:36 -0700198/*
199 * Infrastructure to implement the synchronize_() primitives in
200 * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
201 */
202
203typedef void call_rcu_func_t(struct rcu_head *head,
204 void (*func)(struct rcu_head *head));
205void wait_rcu_gp(call_rcu_func_t crf);
206
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700207#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
Paul E. McKenney64db4cf2008-12-18 21:55:32 +0100208#include <linux/rcutree.h>
Paul E. McKenneya57eb942010-06-29 16:49:16 -0700209#elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU)
Paul E. McKenney9b1d82f2009-10-25 19:03:50 -0700210#include <linux/rcutiny.h>
Paul E. McKenney64db4cf2008-12-18 21:55:32 +0100211#else
212#error "Unknown RCU implementation specified to kernel configuration"
Paul E. McKenney6b3ef482009-08-22 13:56:53 -0700213#endif
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100214
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400215/*
216 * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic
217 * initialization and destruction of rcu_head on the stack. rcu_head structures
218 * allocated dynamically in the heap or defined statically don't need any
219 * initialization.
220 */
221#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
222extern void init_rcu_head_on_stack(struct rcu_head *head);
223extern void destroy_rcu_head_on_stack(struct rcu_head *head);
224#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
Mathieu Desnoyers43760302010-04-17 08:48:39 -0400225static inline void init_rcu_head_on_stack(struct rcu_head *head)
226{
227}
228
229static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
230{
231}
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400232#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
Mathieu Desnoyers43760302010-04-17 08:48:39 -0400233
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700234#ifdef CONFIG_DEBUG_LOCK_ALLOC
Paul E. McKenney632ee202010-02-22 17:04:45 -0800235
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700236extern struct lockdep_map rcu_lock_map;
Paul E. McKenney632ee202010-02-22 17:04:45 -0800237# define rcu_read_acquire() \
238 lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700239# define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_)
Paul E. McKenney632ee202010-02-22 17:04:45 -0800240
241extern struct lockdep_map rcu_bh_lock_map;
242# define rcu_read_acquire_bh() \
243 lock_acquire(&rcu_bh_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
244# define rcu_read_release_bh() lock_release(&rcu_bh_lock_map, 1, _THIS_IP_)
245
246extern struct lockdep_map rcu_sched_lock_map;
247# define rcu_read_acquire_sched() \
248 lock_acquire(&rcu_sched_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
249# define rcu_read_release_sched() \
250 lock_release(&rcu_sched_lock_map, 1, _THIS_IP_)
251
Paul E. McKenneybc293d62010-04-15 12:50:39 -0700252extern int debug_lockdep_rcu_enabled(void);
Paul E. McKenney54dbf962010-03-03 07:46:57 -0800253
Paul E. McKenney632ee202010-02-22 17:04:45 -0800254/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700255 * rcu_read_lock_held() - might we be in RCU read-side critical section?
Paul E. McKenney632ee202010-02-22 17:04:45 -0800256 *
Paul E. McKenneyd20200b2010-03-30 10:52:21 -0700257 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
258 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
Paul E. McKenney632ee202010-02-22 17:04:45 -0800259 * this assumes we are in an RCU read-side critical section unless it can
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700260 * prove otherwise. This is useful for debug checks in functions that
261 * require that they be called within an RCU read-side critical section.
Paul E. McKenney54dbf962010-03-03 07:46:57 -0800262 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700263 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
Paul E. McKenney32c141a2010-03-30 10:59:28 -0700264 * and while lockdep is disabled.
Paul E. McKenney632ee202010-02-22 17:04:45 -0800265 */
266static inline int rcu_read_lock_held(void)
267{
Paul E. McKenney54dbf962010-03-03 07:46:57 -0800268 if (!debug_lockdep_rcu_enabled())
269 return 1;
270 return lock_is_held(&rcu_lock_map);
Paul E. McKenney632ee202010-02-22 17:04:45 -0800271}
272
Paul E. McKenneye3818b82010-03-15 17:03:43 -0700273/*
274 * rcu_read_lock_bh_held() is defined out of line to avoid #include-file
275 * hell.
Paul E. McKenney632ee202010-02-22 17:04:45 -0800276 */
Paul E. McKenneye3818b82010-03-15 17:03:43 -0700277extern int rcu_read_lock_bh_held(void);
Paul E. McKenney632ee202010-02-22 17:04:45 -0800278
279/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700280 * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
Paul E. McKenney632ee202010-02-22 17:04:45 -0800281 *
Paul E. McKenneyd20200b2010-03-30 10:52:21 -0700282 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
283 * RCU-sched read-side critical section. In absence of
284 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
285 * critical section unless it can prove otherwise. Note that disabling
286 * of preemption (including disabling irqs) counts as an RCU-sched
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700287 * read-side critical section. This is useful for debug checks in functions
288 * that required that they be called within an RCU-sched read-side
289 * critical section.
Paul E. McKenney54dbf962010-03-03 07:46:57 -0800290 *
Paul E. McKenney32c141a2010-03-30 10:59:28 -0700291 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
292 * and while lockdep is disabled.
Paul E. McKenney632ee202010-02-22 17:04:45 -0800293 */
Frederic Weisbeckerbdd4e852011-06-08 01:13:27 +0200294#ifdef CONFIG_PREEMPT_COUNT
Paul E. McKenney632ee202010-02-22 17:04:45 -0800295static inline int rcu_read_lock_sched_held(void)
296{
297 int lockdep_opinion = 0;
298
Paul E. McKenney54dbf962010-03-03 07:46:57 -0800299 if (!debug_lockdep_rcu_enabled())
300 return 1;
Paul E. McKenney632ee202010-02-22 17:04:45 -0800301 if (debug_locks)
302 lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
Lai Jiangshan0cff8102010-03-18 12:25:33 -0700303 return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
Paul E. McKenney632ee202010-02-22 17:04:45 -0800304}
Frederic Weisbeckerbdd4e852011-06-08 01:13:27 +0200305#else /* #ifdef CONFIG_PREEMPT_COUNT */
Paul E. McKenneye6033e32010-03-03 17:50:16 -0800306static inline int rcu_read_lock_sched_held(void)
307{
308 return 1;
309}
Frederic Weisbeckerbdd4e852011-06-08 01:13:27 +0200310#endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
Paul E. McKenney632ee202010-02-22 17:04:45 -0800311
312#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
313
314# define rcu_read_acquire() do { } while (0)
315# define rcu_read_release() do { } while (0)
316# define rcu_read_acquire_bh() do { } while (0)
317# define rcu_read_release_bh() do { } while (0)
318# define rcu_read_acquire_sched() do { } while (0)
319# define rcu_read_release_sched() do { } while (0)
320
321static inline int rcu_read_lock_held(void)
322{
323 return 1;
324}
325
326static inline int rcu_read_lock_bh_held(void)
327{
328 return 1;
329}
330
Frederic Weisbeckerbdd4e852011-06-08 01:13:27 +0200331#ifdef CONFIG_PREEMPT_COUNT
Paul E. McKenney632ee202010-02-22 17:04:45 -0800332static inline int rcu_read_lock_sched_held(void)
333{
Paul E. McKenneybbad9372010-04-02 16:17:17 -0700334 return preempt_count() != 0 || irqs_disabled();
Paul E. McKenney632ee202010-02-22 17:04:45 -0800335}
Frederic Weisbeckerbdd4e852011-06-08 01:13:27 +0200336#else /* #ifdef CONFIG_PREEMPT_COUNT */
Paul E. McKenneye6033e32010-03-03 17:50:16 -0800337static inline int rcu_read_lock_sched_held(void)
338{
339 return 1;
340}
Frederic Weisbeckerbdd4e852011-06-08 01:13:27 +0200341#endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
Paul E. McKenney632ee202010-02-22 17:04:45 -0800342
343#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
344
345#ifdef CONFIG_PROVE_RCU
346
Paul E. McKenneyee84b822010-05-06 09:28:41 -0700347extern int rcu_my_thread_group_empty(void);
348
Tetsuo Handa4221a992010-06-26 01:08:19 +0900349/**
350 * rcu_lockdep_assert - emit lockdep splat if specified condition not met
351 * @c: condition to check
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700352 * @s: informative message
Tetsuo Handa4221a992010-06-26 01:08:19 +0900353 */
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700354#define rcu_lockdep_assert(c, s) \
Lai Jiangshan2b3fc352010-04-20 16:23:07 +0800355 do { \
356 static bool __warned; \
357 if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
358 __warned = true; \
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700359 lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
Lai Jiangshan2b3fc352010-04-20 16:23:07 +0800360 } \
361 } while (0)
362
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700363#define rcu_sleep_check() \
364 do { \
365 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map), \
366 "Illegal context switch in RCU-bh" \
367 " read-side critical section"); \
368 rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map), \
369 "Illegal context switch in RCU-sched"\
370 " read-side critical section"); \
371 } while (0)
372
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700373#else /* #ifdef CONFIG_PROVE_RCU */
374
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700375#define rcu_lockdep_assert(c, s) do { } while (0)
376#define rcu_sleep_check() do { } while (0)
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700377
378#endif /* #else #ifdef CONFIG_PROVE_RCU */
379
380/*
381 * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
382 * and rcu_assign_pointer(). Some of these could be folded into their
383 * callers, but they are left separate in order to ease introduction of
384 * multiple flavors of pointers to match the multiple flavors of RCU
385 * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in
386 * the future.
387 */
Paul E. McKenney53ecfba2010-09-13 17:24:21 -0700388
389#ifdef __CHECKER__
390#define rcu_dereference_sparse(p, space) \
391 ((void)(((typeof(*p) space *)p) == p))
392#else /* #ifdef __CHECKER__ */
393#define rcu_dereference_sparse(p, space)
394#endif /* #else #ifdef __CHECKER__ */
395
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700396#define __rcu_access_pointer(p, space) \
397 ({ \
398 typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
Paul E. McKenney53ecfba2010-09-13 17:24:21 -0700399 rcu_dereference_sparse(p, space); \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700400 ((typeof(*p) __force __kernel *)(_________p1)); \
401 })
402#define __rcu_dereference_check(p, c, space) \
403 ({ \
404 typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700405 rcu_lockdep_assert(c, "suspicious rcu_dereference_check()" \
406 " usage"); \
Paul E. McKenney53ecfba2010-09-13 17:24:21 -0700407 rcu_dereference_sparse(p, space); \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700408 smp_read_barrier_depends(); \
409 ((typeof(*p) __force __kernel *)(_________p1)); \
410 })
411#define __rcu_dereference_protected(p, c, space) \
412 ({ \
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700413 rcu_lockdep_assert(c, "suspicious rcu_dereference_protected()" \
414 " usage"); \
Paul E. McKenney53ecfba2010-09-13 17:24:21 -0700415 rcu_dereference_sparse(p, space); \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700416 ((typeof(*p) __force __kernel *)(p)); \
417 })
418
Paul E. McKenneya4dd9922011-04-01 07:15:14 -0700419#define __rcu_access_index(p, space) \
420 ({ \
421 typeof(p) _________p1 = ACCESS_ONCE(p); \
422 rcu_dereference_sparse(p, space); \
423 (_________p1); \
424 })
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700425#define __rcu_dereference_index_check(p, c) \
426 ({ \
427 typeof(p) _________p1 = ACCESS_ONCE(p); \
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700428 rcu_lockdep_assert(c, \
429 "suspicious rcu_dereference_index_check()" \
430 " usage"); \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700431 smp_read_barrier_depends(); \
432 (_________p1); \
433 })
434#define __rcu_assign_pointer(p, v, space) \
435 ({ \
Eric Dumazetd322f452011-07-31 22:09:25 -0700436 smp_wmb(); \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700437 (p) = (typeof(*v) __force space *)(v); \
438 })
439
440
Paul E. McKenney632ee202010-02-22 17:04:45 -0800441/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700442 * rcu_access_pointer() - fetch RCU pointer with no dereferencing
443 * @p: The pointer to read
444 *
445 * Return the value of the specified RCU-protected pointer, but omit the
446 * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful
447 * when the value of this pointer is accessed, but the pointer is not
448 * dereferenced, for example, when testing an RCU-protected pointer against
449 * NULL. Although rcu_access_pointer() may also be used in cases where
450 * update-side locks prevent the value of the pointer from changing, you
451 * should instead use rcu_dereference_protected() for this use case.
452 */
453#define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
454
455/**
456 * rcu_dereference_check() - rcu_dereference with debug checking
David Howellsc08c68d2010-04-09 15:39:11 -0700457 * @p: The pointer to read, prior to dereferencing
458 * @c: The conditions under which the dereference will take place
Paul E. McKenney632ee202010-02-22 17:04:45 -0800459 *
David Howellsc08c68d2010-04-09 15:39:11 -0700460 * Do an rcu_dereference(), but check that the conditions under which the
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700461 * dereference will take place are correct. Typically the conditions
462 * indicate the various locking conditions that should be held at that
463 * point. The check should return true if the conditions are satisfied.
464 * An implicit check for being in an RCU read-side critical section
465 * (rcu_read_lock()) is included.
David Howellsc08c68d2010-04-09 15:39:11 -0700466 *
467 * For example:
468 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700469 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
David Howellsc08c68d2010-04-09 15:39:11 -0700470 *
471 * could be used to indicate to lockdep that foo->bar may only be dereferenced
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700472 * if either rcu_read_lock() is held, or that the lock required to replace
David Howellsc08c68d2010-04-09 15:39:11 -0700473 * the bar struct at foo->bar is held.
474 *
475 * Note that the list of conditions may also include indications of when a lock
476 * need not be held, for example during initialisation or destruction of the
477 * target struct:
478 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700479 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
David Howellsc08c68d2010-04-09 15:39:11 -0700480 * atomic_read(&foo->usage) == 0);
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700481 *
482 * Inserts memory barriers on architectures that require them
483 * (currently only the Alpha), prevents the compiler from refetching
484 * (and from merging fetches), and, more importantly, documents exactly
485 * which pointers are protected by RCU and checks that the pointer is
486 * annotated as __rcu.
Paul E. McKenney632ee202010-02-22 17:04:45 -0800487 */
488#define rcu_dereference_check(p, c) \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700489 __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)
Paul E. McKenney632ee202010-02-22 17:04:45 -0800490
Paul E. McKenneyb62730b2010-04-09 15:39:10 -0700491/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700492 * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
493 * @p: The pointer to read, prior to dereferencing
494 * @c: The conditions under which the dereference will take place
495 *
496 * This is the RCU-bh counterpart to rcu_dereference_check().
497 */
498#define rcu_dereference_bh_check(p, c) \
499 __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu)
500
501/**
502 * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
503 * @p: The pointer to read, prior to dereferencing
504 * @c: The conditions under which the dereference will take place
505 *
506 * This is the RCU-sched counterpart to rcu_dereference_check().
507 */
508#define rcu_dereference_sched_check(p, c) \
509 __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \
510 __rcu)
511
512#define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/
513
514/**
Paul E. McKenneya4dd9922011-04-01 07:15:14 -0700515 * rcu_access_index() - fetch RCU index with no dereferencing
516 * @p: The index to read
517 *
518 * Return the value of the specified RCU-protected index, but omit the
519 * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful
520 * when the value of this index is accessed, but the index is not
521 * dereferenced, for example, when testing an RCU-protected index against
522 * -1. Although rcu_access_index() may also be used in cases where
523 * update-side locks prevent the value of the index from changing, you
524 * should instead use rcu_dereference_index_protected() for this use case.
525 */
526#define rcu_access_index(p) __rcu_access_index((p), __rcu)
527
528/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700529 * rcu_dereference_index_check() - rcu_dereference for indices with debug checking
530 * @p: The pointer to read, prior to dereferencing
531 * @c: The conditions under which the dereference will take place
532 *
533 * Similar to rcu_dereference_check(), but omits the sparse checking.
534 * This allows rcu_dereference_index_check() to be used on integers,
535 * which can then be used as array indices. Attempting to use
536 * rcu_dereference_check() on an integer will give compiler warnings
537 * because the sparse address-space mechanism relies on dereferencing
538 * the RCU-protected pointer. Dereferencing integers is not something
539 * that even gcc will put up with.
540 *
541 * Note that this function does not implicitly check for RCU read-side
542 * critical sections. If this function gains lots of uses, it might
543 * make sense to provide versions for each flavor of RCU, but it does
544 * not make sense as of early 2010.
545 */
546#define rcu_dereference_index_check(p, c) \
547 __rcu_dereference_index_check((p), (c))
548
549/**
550 * rcu_dereference_protected() - fetch RCU pointer when updates prevented
551 * @p: The pointer to read, prior to dereferencing
552 * @c: The conditions under which the dereference will take place
Paul E. McKenneyb62730b2010-04-09 15:39:10 -0700553 *
554 * Return the value of the specified RCU-protected pointer, but omit
555 * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This
556 * is useful in cases where update-side locks prevent the value of the
557 * pointer from changing. Please note that this primitive does -not-
558 * prevent the compiler from repeating this reference or combining it
559 * with other references, so it should not be used without protection
560 * of appropriate locks.
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700561 *
562 * This function is only for update-side use. Using this function
563 * when protected only by rcu_read_lock() will result in infrequent
564 * but very ugly failures.
Paul E. McKenneyb62730b2010-04-09 15:39:10 -0700565 */
566#define rcu_dereference_protected(p, c) \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700567 __rcu_dereference_protected((p), (c), __rcu)
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700568
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700569
570/**
571 * rcu_dereference() - fetch RCU-protected pointer for dereferencing
572 * @p: The pointer to read, prior to dereferencing
573 *
574 * This is a simple wrapper around rcu_dereference_check().
575 */
576#define rcu_dereference(p) rcu_dereference_check(p, 0)
577
578/**
579 * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
580 * @p: The pointer to read, prior to dereferencing
581 *
582 * Makes rcu_dereference_check() do the dirty work.
583 */
584#define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
585
586/**
587 * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
588 * @p: The pointer to read, prior to dereferencing
589 *
590 * Makes rcu_dereference_check() do the dirty work.
591 */
592#define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
593
594/**
595 * rcu_read_lock() - mark the beginning of an RCU read-side critical section
Linus Torvalds1da177e2005-04-16 15:20:36 -0700596 *
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700597 * When synchronize_rcu() is invoked on one CPU while other CPUs
Linus Torvalds1da177e2005-04-16 15:20:36 -0700598 * are within RCU read-side critical sections, then the
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700599 * synchronize_rcu() is guaranteed to block until after all the other
Linus Torvalds1da177e2005-04-16 15:20:36 -0700600 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
601 * on one CPU while other CPUs are within RCU read-side critical
602 * sections, invocation of the corresponding RCU callback is deferred
603 * until after the all the other CPUs exit their critical sections.
604 *
605 * Note, however, that RCU callbacks are permitted to run concurrently
Paul E. McKenney77d84852010-07-08 17:38:59 -0700606 * with new RCU read-side critical sections. One way that this can happen
Linus Torvalds1da177e2005-04-16 15:20:36 -0700607 * is via the following sequence of events: (1) CPU 0 enters an RCU
608 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
609 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
610 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
611 * callback is invoked. This is legal, because the RCU read-side critical
612 * section that was running concurrently with the call_rcu() (and which
613 * therefore might be referencing something that the corresponding RCU
614 * callback would free up) has completed before the corresponding
615 * RCU callback is invoked.
616 *
617 * RCU read-side critical sections may be nested. Any deferred actions
618 * will be deferred until the outermost RCU read-side critical section
619 * completes.
620 *
Paul E. McKenney9079fd72010-08-07 21:59:54 -0700621 * You can avoid reading and understanding the next paragraph by
622 * following this rule: don't put anything in an rcu_read_lock() RCU
623 * read-side critical section that would block in a !PREEMPT kernel.
624 * But if you want the full story, read on!
625 *
626 * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it
627 * is illegal to block while in an RCU read-side critical section. In
628 * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU)
629 * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may
630 * be preempted, but explicit blocking is illegal. Finally, in preemptible
631 * RCU implementations in real-time (CONFIG_PREEMPT_RT) kernel builds,
632 * RCU read-side critical sections may be preempted and they may also
633 * block, but only when acquiring spinlocks that are subject to priority
634 * inheritance.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700635 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700636static inline void rcu_read_lock(void)
637{
638 __rcu_read_lock();
639 __acquire(RCU);
640 rcu_read_acquire();
641}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700642
Linus Torvalds1da177e2005-04-16 15:20:36 -0700643/*
644 * So where is rcu_write_lock()? It does not exist, as there is no
645 * way for writers to lock out RCU readers. This is a feature, not
646 * a bug -- this property is what provides RCU's performance benefits.
647 * Of course, writers must coordinate with each other. The normal
648 * spinlock primitives work well for this, but any other technique may be
649 * used as well. RCU does not care how the writers keep out of each
650 * others' way, as long as they do so.
651 */
Paul E. McKenney3d76c082009-09-28 07:46:32 -0700652
653/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700654 * rcu_read_unlock() - marks the end of an RCU read-side critical section.
Paul E. McKenney3d76c082009-09-28 07:46:32 -0700655 *
656 * See rcu_read_lock() for more information.
657 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700658static inline void rcu_read_unlock(void)
659{
660 rcu_read_release();
661 __release(RCU);
662 __rcu_read_unlock();
663}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700664
665/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700666 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
Linus Torvalds1da177e2005-04-16 15:20:36 -0700667 *
668 * This is equivalent of rcu_read_lock(), but to be used when updates
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700669 * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since
670 * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a
671 * softirq handler to be a quiescent state, a process in RCU read-side
672 * critical section must be protected by disabling softirqs. Read-side
673 * critical sections in interrupt context can use just rcu_read_lock(),
674 * though this should at least be commented to avoid confusing people
675 * reading the code.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700676 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700677static inline void rcu_read_lock_bh(void)
678{
Paul E. McKenney6206ab92011-08-01 06:22:11 -0700679 local_bh_disable();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700680 __acquire(RCU_BH);
Paul E. McKenney632ee202010-02-22 17:04:45 -0800681 rcu_read_acquire_bh();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700682}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700683
684/*
685 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
686 *
687 * See rcu_read_lock_bh() for more information.
688 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700689static inline void rcu_read_unlock_bh(void)
690{
Paul E. McKenney632ee202010-02-22 17:04:45 -0800691 rcu_read_release_bh();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700692 __release(RCU_BH);
Paul E. McKenney6206ab92011-08-01 06:22:11 -0700693 local_bh_enable();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700694}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700695
696/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700697 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400698 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700699 * This is equivalent of rcu_read_lock(), but to be used when updates
700 * are being done using call_rcu_sched() or synchronize_rcu_sched().
701 * Read-side critical sections can also be introduced by anything that
702 * disables preemption, including local_irq_disable() and friends.
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400703 */
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700704static inline void rcu_read_lock_sched(void)
705{
706 preempt_disable();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700707 __acquire(RCU_SCHED);
Paul E. McKenney632ee202010-02-22 17:04:45 -0800708 rcu_read_acquire_sched();
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700709}
Paul E. McKenney1eba8f82009-09-23 09:50:42 -0700710
711/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
Paul E. McKenney7c614d62009-08-24 09:42:00 -0700712static inline notrace void rcu_read_lock_sched_notrace(void)
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700713{
714 preempt_disable_notrace();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700715 __acquire(RCU_SCHED);
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700716}
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400717
718/*
719 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
720 *
721 * See rcu_read_lock_sched for more information.
722 */
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700723static inline void rcu_read_unlock_sched(void)
724{
Paul E. McKenney632ee202010-02-22 17:04:45 -0800725 rcu_read_release_sched();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700726 __release(RCU_SCHED);
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700727 preempt_enable();
728}
Paul E. McKenney1eba8f82009-09-23 09:50:42 -0700729
730/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
Paul E. McKenney7c614d62009-08-24 09:42:00 -0700731static inline notrace void rcu_read_unlock_sched_notrace(void)
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700732{
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700733 __release(RCU_SCHED);
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700734 preempt_enable_notrace();
735}
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400736
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400737/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700738 * rcu_assign_pointer() - assign to RCU-protected pointer
739 * @p: pointer to assign to
740 * @v: value to assign (publish)
Paul E. McKenneyc26d34a2010-02-22 17:04:46 -0800741 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700742 * Assigns the specified value to the specified RCU-protected
743 * pointer, ensuring that any concurrent RCU readers will see
744 * any prior initialization. Returns the value assigned.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700745 *
746 * Inserts memory barriers on architectures that require them
Paul E. McKenney6846c0c2011-07-31 22:33:02 -0700747 * (which is most of them), and also prevents the compiler from
748 * reordering the code that initializes the structure after the pointer
749 * assignment. More importantly, this call documents which pointers
750 * will be dereferenced by RCU read-side code.
751 *
752 * In some special cases, you may use RCU_INIT_POINTER() instead
753 * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due
754 * to the fact that it does not constrain either the CPU or the compiler.
755 * That said, using RCU_INIT_POINTER() when you should have used
756 * rcu_assign_pointer() is a very bad thing that results in
757 * impossible-to-diagnose memory corruption. So please be careful.
758 * See the RCU_INIT_POINTER() comment header for details.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700759 */
Paul E. McKenneyd99c4f62008-02-06 01:37:25 -0800760#define rcu_assign_pointer(p, v) \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700761 __rcu_assign_pointer((p), (v), __rcu)
762
763/**
764 * RCU_INIT_POINTER() - initialize an RCU protected pointer
765 *
Paul E. McKenney6846c0c2011-07-31 22:33:02 -0700766 * Initialize an RCU-protected pointer in special cases where readers
767 * do not need ordering constraints on the CPU or the compiler. These
768 * special cases are:
769 *
770 * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer -or-
771 * 2. The caller has taken whatever steps are required to prevent
772 * RCU readers from concurrently accessing this pointer -or-
773 * 3. The referenced data structure has already been exposed to
774 * readers either at compile time or via rcu_assign_pointer() -and-
775 * a. You have not made -any- reader-visible changes to
776 * this structure since then -or-
777 * b. It is OK for readers accessing this structure from its
778 * new location to see the old state of the structure. (For
779 * example, the changes were to statistical counters or to
780 * other state where exact synchronization is not required.)
781 *
782 * Failure to follow these rules governing use of RCU_INIT_POINTER() will
783 * result in impossible-to-diagnose memory corruption. As in the structures
784 * will look OK in crash dumps, but any concurrent RCU readers might
785 * see pre-initialized values of the referenced data structure. So
786 * please be very careful how you use RCU_INIT_POINTER()!!!
787 *
788 * If you are creating an RCU-protected linked structure that is accessed
789 * by a single external-to-structure RCU-protected pointer, then you may
790 * use RCU_INIT_POINTER() to initialize the internal RCU-protected
791 * pointers, but you must use rcu_assign_pointer() to initialize the
792 * external-to-structure pointer -after- you have completely initialized
793 * the reader-accessible portions of the linked structure.
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700794 */
795#define RCU_INIT_POINTER(p, v) \
796 p = (typeof(*v) __force __rcu *)(v)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700797
Lai Jiangshan9ab15442011-03-18 11:15:47 +0800798static __always_inline bool __is_kfree_rcu_offset(unsigned long offset)
799{
800 return offset < 4096;
801}
802
803static __always_inline
804void __kfree_rcu(struct rcu_head *head, unsigned long offset)
805{
806 typedef void (*rcu_callback)(struct rcu_head *);
807
808 BUILD_BUG_ON(!__builtin_constant_p(offset));
809
810 /* See the kfree_rcu() header comment. */
811 BUILD_BUG_ON(!__is_kfree_rcu_offset(offset));
812
813 call_rcu(head, (rcu_callback)offset);
814}
815
Lai Jiangshan9ab15442011-03-18 11:15:47 +0800816/**
817 * kfree_rcu() - kfree an object after a grace period.
818 * @ptr: pointer to kfree
819 * @rcu_head: the name of the struct rcu_head within the type of @ptr.
820 *
821 * Many rcu callbacks functions just call kfree() on the base structure.
822 * These functions are trivial, but their size adds up, and furthermore
823 * when they are used in a kernel module, that module must invoke the
824 * high-latency rcu_barrier() function at module-unload time.
825 *
826 * The kfree_rcu() function handles this issue. Rather than encoding a
827 * function address in the embedded rcu_head structure, kfree_rcu() instead
828 * encodes the offset of the rcu_head structure within the base structure.
829 * Because the functions are not allowed in the low-order 4096 bytes of
830 * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
831 * If the offset is larger than 4095 bytes, a compile-time error will
832 * be generated in __kfree_rcu(). If this error is triggered, you can
833 * either fall back to use of call_rcu() or rearrange the structure to
834 * position the rcu_head structure into the first 4096 bytes.
835 *
836 * Note that the allowable offset might decrease in the future, for example,
837 * to allow something like kmem_cache_free_rcu().
838 */
839#define kfree_rcu(ptr, rcu_head) \
840 __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
841
Linus Torvalds1da177e2005-04-16 15:20:36 -0700842#endif /* __LINUX_RCUPDATE_H */