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, you can access it online at
16 * http://www.gnu.org/licenses/gpl-2.0.html.
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/types.h>
37 #include <linux/cache.h>
38 #include <linux/spinlock.h>
39 #include <linux/threads.h>
40 #include <linux/cpumask.h>
41 #include <linux/seqlock.h>
42 #include <linux/lockdep.h>
43 #include <linux/completion.h>
44 #include <linux/debugobjects.h>
45 #include <linux/bug.h>
46 #include <linux/compiler.h>
47 #include <linux/ktime.h>
49 #include <asm/barrier.h>
51 extern int rcu_expedited; /* for sysctl */
53 #ifdef CONFIG_TINY_RCU
54 /* Tiny RCU doesn't expedite, as its purpose in life is instead to be tiny. */
55 static inline bool rcu_gp_is_expedited(void) /* Internal RCU use. */
60 static inline void rcu_expedite_gp(void)
64 static inline void rcu_unexpedite_gp(void)
67 #else /* #ifdef CONFIG_TINY_RCU */
68 bool rcu_gp_is_expedited(void); /* Internal RCU use. */
69 void rcu_expedite_gp(void);
70 void rcu_unexpedite_gp(void);
71 #endif /* #else #ifdef CONFIG_TINY_RCU */
73 enum rcutorture_type {
82 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
83 void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
84 unsigned long *gpnum, unsigned long *completed);
85 void rcutorture_record_test_transition(void);
86 void rcutorture_record_progress(unsigned long vernum);
87 void do_trace_rcu_torture_read(const char *rcutorturename,
93 static inline void rcutorture_get_gp_data(enum rcutorture_type test_type,
96 unsigned long *completed)
102 static inline void rcutorture_record_test_transition(void)
105 static inline void rcutorture_record_progress(unsigned long vernum)
108 #ifdef CONFIG_RCU_TRACE
109 void do_trace_rcu_torture_read(const char *rcutorturename,
110 struct rcu_head *rhp,
115 #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
120 #define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b))
121 #define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b))
122 #define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))
123 #define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b))
124 #define ulong2long(a) (*(long *)(&(a)))
126 /* Exported common interfaces */
128 #ifdef CONFIG_PREEMPT_RCU
131 * call_rcu() - Queue an RCU callback for invocation after a grace period.
132 * @head: structure to be used for queueing the RCU updates.
133 * @func: actual callback function to be invoked after the grace period
135 * The callback function will be invoked some time after a full grace
136 * period elapses, in other words after all pre-existing RCU read-side
137 * critical sections have completed. However, the callback function
138 * might well execute concurrently with RCU read-side critical sections
139 * that started after call_rcu() was invoked. RCU read-side critical
140 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
143 * Note that all CPUs must agree that the grace period extended beyond
144 * all pre-existing RCU read-side critical section. On systems with more
145 * than one CPU, this means that when "func()" is invoked, each CPU is
146 * guaranteed to have executed a full memory barrier since the end of its
147 * last RCU read-side critical section whose beginning preceded the call
148 * to call_rcu(). It also means that each CPU executing an RCU read-side
149 * critical section that continues beyond the start of "func()" must have
150 * executed a memory barrier after the call_rcu() but before the beginning
151 * of that RCU read-side critical section. Note that these guarantees
152 * include CPUs that are offline, idle, or executing in user mode, as
153 * well as CPUs that are executing in the kernel.
155 * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
156 * resulting RCU callback function "func()", then both CPU A and CPU B are
157 * guaranteed to execute a full memory barrier during the time interval
158 * between the call to call_rcu() and the invocation of "func()" -- even
159 * if CPU A and CPU B are the same CPU (but again only if the system has
160 * more than one CPU).
162 void call_rcu(struct rcu_head *head,
163 rcu_callback_t func);
165 #else /* #ifdef CONFIG_PREEMPT_RCU */
167 /* In classic RCU, call_rcu() is just call_rcu_sched(). */
168 #define call_rcu call_rcu_sched
170 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
172 #ifdef CONFIG_PREEMPT_RT_FULL
173 #define call_rcu_bh call_rcu
176 * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
177 * @head: structure to be used for queueing the RCU updates.
178 * @func: actual callback function to be invoked after the grace period
180 * The callback function will be invoked some time after a full grace
181 * period elapses, in other words after all currently executing RCU
182 * read-side critical sections have completed. call_rcu_bh() assumes
183 * that the read-side critical sections end on completion of a softirq
184 * handler. This means that read-side critical sections in process
185 * context must not be interrupted by softirqs. This interface is to be
186 * used when most of the read-side critical sections are in softirq context.
187 * RCU read-side critical sections are delimited by :
188 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
190 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
191 * These may be nested.
193 * See the description of call_rcu() for more detailed information on
194 * memory ordering guarantees.
196 void call_rcu_bh(struct rcu_head *head,
197 rcu_callback_t func);
201 * call_rcu_sched() - Queue an RCU for invocation after sched grace period.
202 * @head: structure to be used for queueing the RCU updates.
203 * @func: actual callback function to be invoked after the grace period
205 * The callback function will be invoked some time after a full grace
206 * period elapses, in other words after all currently executing RCU
207 * read-side critical sections have completed. call_rcu_sched() assumes
208 * that the read-side critical sections end on enabling of preemption
209 * or on voluntary preemption.
210 * RCU read-side critical sections are delimited by :
211 * - rcu_read_lock_sched() and rcu_read_unlock_sched(),
213 * anything that disables preemption.
214 * These may be nested.
216 * See the description of call_rcu() for more detailed information on
217 * memory ordering guarantees.
219 void call_rcu_sched(struct rcu_head *head,
220 rcu_callback_t func);
222 void synchronize_sched(void);
225 * Structure allowing asynchronous waiting on RCU.
227 struct rcu_synchronize {
228 struct rcu_head head;
229 struct completion completion;
231 void wakeme_after_rcu(struct rcu_head *head);
233 void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
234 struct rcu_synchronize *rs_array);
236 #define _wait_rcu_gp(checktiny, ...) \
238 call_rcu_func_t __crcu_array[] = { __VA_ARGS__ }; \
239 struct rcu_synchronize __rs_array[ARRAY_SIZE(__crcu_array)]; \
240 __wait_rcu_gp(checktiny, ARRAY_SIZE(__crcu_array), \
241 __crcu_array, __rs_array); \
244 #define wait_rcu_gp(...) _wait_rcu_gp(false, __VA_ARGS__)
247 * synchronize_rcu_mult - Wait concurrently for multiple grace periods
248 * @...: List of call_rcu() functions for the flavors to wait on.
250 * This macro waits concurrently for multiple flavors of RCU grace periods.
251 * For example, synchronize_rcu_mult(call_rcu, call_rcu_bh) would wait
252 * on concurrent RCU and RCU-bh grace periods. Waiting on a give SRCU
253 * domain requires you to write a wrapper function for that SRCU domain's
254 * call_srcu() function, supplying the corresponding srcu_struct.
256 * If Tiny RCU, tell _wait_rcu_gp() not to bother waiting for RCU
257 * or RCU-bh, given that anywhere synchronize_rcu_mult() can be called
258 * is automatically a grace period.
260 #define synchronize_rcu_mult(...) \
261 _wait_rcu_gp(IS_ENABLED(CONFIG_TINY_RCU), __VA_ARGS__)
264 * call_rcu_tasks() - Queue an RCU for invocation task-based grace period
265 * @head: structure to be used for queueing the RCU updates.
266 * @func: actual callback function to be invoked after the grace period
268 * The callback function will be invoked some time after a full grace
269 * period elapses, in other words after all currently executing RCU
270 * read-side critical sections have completed. call_rcu_tasks() assumes
271 * that the read-side critical sections end at a voluntary context
272 * switch (not a preemption!), entry into idle, or transition to usermode
273 * execution. As such, there are no read-side primitives analogous to
274 * rcu_read_lock() and rcu_read_unlock() because this primitive is intended
275 * to determine that all tasks have passed through a safe state, not so
276 * much for data-strcuture synchronization.
278 * See the description of call_rcu() for more detailed information on
279 * memory ordering guarantees.
281 void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
282 void synchronize_rcu_tasks(void);
283 void rcu_barrier_tasks(void);
285 #ifdef CONFIG_PREEMPT_RCU
287 void __rcu_read_lock(void);
288 void __rcu_read_unlock(void);
289 void rcu_read_unlock_special(struct task_struct *t);
290 void synchronize_rcu(void);
293 * Defined as a macro as it is a very low level header included from
294 * areas that don't even know about current. This gives the rcu_read_lock()
295 * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
296 * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
298 #define rcu_preempt_depth() (current->rcu_read_lock_nesting)
299 #ifndef CONFIG_PREEMPT_RT_FULL
300 #define sched_rcu_preempt_depth() rcu_preempt_depth()
302 static inline int sched_rcu_preempt_depth(void) { return 0; }
305 #else /* #ifdef CONFIG_PREEMPT_RCU */
307 static inline void __rcu_read_lock(void)
309 if (IS_ENABLED(CONFIG_PREEMPT_COUNT))
313 static inline void __rcu_read_unlock(void)
315 if (IS_ENABLED(CONFIG_PREEMPT_COUNT))
319 static inline void synchronize_rcu(void)
324 static inline int rcu_preempt_depth(void)
329 #define sched_rcu_preempt_depth() rcu_preempt_depth()
331 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
333 /* Internal to kernel */
335 void rcu_end_inkernel_boot(void);
336 void rcu_sched_qs(void);
337 void rcu_bh_qs(void);
338 void rcu_check_callbacks(int user);
339 struct notifier_block;
340 int rcu_cpu_notify(struct notifier_block *self,
341 unsigned long action, void *hcpu);
343 #ifdef CONFIG_RCU_STALL_COMMON
344 void rcu_sysrq_start(void);
345 void rcu_sysrq_end(void);
346 #else /* #ifdef CONFIG_RCU_STALL_COMMON */
347 static inline void rcu_sysrq_start(void)
350 static inline void rcu_sysrq_end(void)
353 #endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
355 #ifdef CONFIG_NO_HZ_FULL
356 void rcu_user_enter(void);
357 void rcu_user_exit(void);
359 static inline void rcu_user_enter(void) { }
360 static inline void rcu_user_exit(void) { }
361 static inline void rcu_user_hooks_switch(struct task_struct *prev,
362 struct task_struct *next) { }
363 #endif /* CONFIG_NO_HZ_FULL */
365 #ifdef CONFIG_RCU_NOCB_CPU
366 void rcu_init_nohz(void);
367 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
368 static inline void rcu_init_nohz(void)
371 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
374 * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
375 * @a: Code that RCU needs to pay attention to.
377 * RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden
378 * in the inner idle loop, that is, between the rcu_idle_enter() and
379 * the rcu_idle_exit() -- RCU will happily ignore any such read-side
380 * critical sections. However, things like powertop need tracepoints
381 * in the inner idle loop.
383 * This macro provides the way out: RCU_NONIDLE(do_something_with_RCU())
384 * will tell RCU that it needs to pay attending, invoke its argument
385 * (in this example, a call to the do_something_with_RCU() function),
386 * and then tell RCU to go back to ignoring this CPU. It is permissible
387 * to nest RCU_NONIDLE() wrappers, but the nesting level is currently
388 * quite limited. If deeper nesting is required, it will be necessary
389 * to adjust DYNTICK_TASK_NESTING_VALUE accordingly.
391 #define RCU_NONIDLE(a) \
394 do { a; } while (0); \
399 * Note a voluntary context switch for RCU-tasks benefit. This is a
400 * macro rather than an inline function to avoid #include hell.
402 #ifdef CONFIG_TASKS_RCU
403 #define TASKS_RCU(x) x
404 extern struct srcu_struct tasks_rcu_exit_srcu;
405 #define rcu_note_voluntary_context_switch(t) \
408 if (READ_ONCE((t)->rcu_tasks_holdout)) \
409 WRITE_ONCE((t)->rcu_tasks_holdout, false); \
411 #else /* #ifdef CONFIG_TASKS_RCU */
412 #define TASKS_RCU(x) do { } while (0)
413 #define rcu_note_voluntary_context_switch(t) rcu_all_qs()
414 #endif /* #else #ifdef CONFIG_TASKS_RCU */
417 * cond_resched_rcu_qs - Report potential quiescent states to RCU
419 * This macro resembles cond_resched(), except that it is defined to
420 * report potential quiescent states to RCU-tasks even if the cond_resched()
421 * machinery were to be shut off, as some advocate for PREEMPT kernels.
423 #define cond_resched_rcu_qs() \
425 if (!cond_resched()) \
426 rcu_note_voluntary_context_switch(current); \
429 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP)
430 bool __rcu_is_watching(void);
431 #endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP) */
434 * Infrastructure to implement the synchronize_() primitives in
435 * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
438 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
439 #include <linux/rcutree.h>
440 #elif defined(CONFIG_TINY_RCU)
441 #include <linux/rcutiny.h>
443 #error "Unknown RCU implementation specified to kernel configuration"
447 * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic
448 * initialization and destruction of rcu_head on the stack. rcu_head structures
449 * allocated dynamically in the heap or defined statically don't need any
452 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
453 void init_rcu_head(struct rcu_head *head);
454 void destroy_rcu_head(struct rcu_head *head);
455 void init_rcu_head_on_stack(struct rcu_head *head);
456 void destroy_rcu_head_on_stack(struct rcu_head *head);
457 #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
458 static inline void init_rcu_head(struct rcu_head *head)
462 static inline void destroy_rcu_head(struct rcu_head *head)
466 static inline void init_rcu_head_on_stack(struct rcu_head *head)
470 static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
473 #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
475 #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
476 bool rcu_lockdep_current_cpu_online(void);
477 #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
478 static inline bool rcu_lockdep_current_cpu_online(void)
482 #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
484 #ifdef CONFIG_DEBUG_LOCK_ALLOC
486 static inline void rcu_lock_acquire(struct lockdep_map *map)
488 lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
491 static inline void rcu_lock_release(struct lockdep_map *map)
493 lock_release(map, 1, _THIS_IP_);
496 extern struct lockdep_map rcu_lock_map;
497 extern struct lockdep_map rcu_bh_lock_map;
498 extern struct lockdep_map rcu_sched_lock_map;
499 extern struct lockdep_map rcu_callback_map;
500 int debug_lockdep_rcu_enabled(void);
502 int rcu_read_lock_held(void);
503 #ifdef CONFIG_PREEMPT_RT_FULL
504 static inline int rcu_read_lock_bh_held(void)
506 return rcu_read_lock_held();
509 int rcu_read_lock_bh_held(void);
513 * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
515 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
516 * RCU-sched read-side critical section. In absence of
517 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
518 * critical section unless it can prove otherwise.
520 #ifdef CONFIG_PREEMPT_COUNT
521 int rcu_read_lock_sched_held(void);
522 #else /* #ifdef CONFIG_PREEMPT_COUNT */
523 static inline int rcu_read_lock_sched_held(void)
527 #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
529 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
531 # define rcu_lock_acquire(a) do { } while (0)
532 # define rcu_lock_release(a) do { } while (0)
534 static inline int rcu_read_lock_held(void)
539 static inline int rcu_read_lock_bh_held(void)
544 #ifdef CONFIG_PREEMPT_COUNT
545 static inline int rcu_read_lock_sched_held(void)
547 return preempt_count() != 0 || irqs_disabled();
549 #else /* #ifdef CONFIG_PREEMPT_COUNT */
550 static inline int rcu_read_lock_sched_held(void)
554 #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
556 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
558 #ifdef CONFIG_PROVE_RCU
561 * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met
562 * @c: condition to check
563 * @s: informative message
565 #define RCU_LOCKDEP_WARN(c, s) \
567 static bool __section(.data.unlikely) __warned; \
568 if (debug_lockdep_rcu_enabled() && !__warned && (c)) { \
570 lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
574 #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
575 static inline void rcu_preempt_sleep_check(void)
577 RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
578 "Illegal context switch in RCU read-side critical section");
580 #else /* #ifdef CONFIG_PROVE_RCU */
581 static inline void rcu_preempt_sleep_check(void)
584 #endif /* #else #ifdef CONFIG_PROVE_RCU */
586 #define rcu_sleep_check() \
588 rcu_preempt_sleep_check(); \
589 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map), \
590 "Illegal context switch in RCU-bh read-side critical section"); \
591 RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), \
592 "Illegal context switch in RCU-sched read-side critical section"); \
595 #else /* #ifdef CONFIG_PROVE_RCU */
597 #define RCU_LOCKDEP_WARN(c, s) do { } while (0)
598 #define rcu_sleep_check() do { } while (0)
600 #endif /* #else #ifdef CONFIG_PROVE_RCU */
603 * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
604 * and rcu_assign_pointer(). Some of these could be folded into their
605 * callers, but they are left separate in order to ease introduction of
606 * multiple flavors of pointers to match the multiple flavors of RCU
607 * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in
612 #define rcu_dereference_sparse(p, space) \
613 ((void)(((typeof(*p) space *)p) == p))
614 #else /* #ifdef __CHECKER__ */
615 #define rcu_dereference_sparse(p, space)
616 #endif /* #else #ifdef __CHECKER__ */
618 #define __rcu_access_pointer(p, space) \
620 typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \
621 rcu_dereference_sparse(p, space); \
622 ((typeof(*p) __force __kernel *)(_________p1)); \
624 #define __rcu_dereference_check(p, c, space) \
626 /* Dependency order vs. p above. */ \
627 typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \
628 RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
629 rcu_dereference_sparse(p, space); \
630 ((typeof(*p) __force __kernel *)(________p1)); \
632 #define __rcu_dereference_protected(p, c, space) \
634 RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
635 rcu_dereference_sparse(p, space); \
636 ((typeof(*p) __force __kernel *)(p)); \
640 * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
641 * @v: The value to statically initialize with.
643 #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
646 * rcu_assign_pointer() - assign to RCU-protected pointer
647 * @p: pointer to assign to
648 * @v: value to assign (publish)
650 * Assigns the specified value to the specified RCU-protected
651 * pointer, ensuring that any concurrent RCU readers will see
652 * any prior initialization.
654 * Inserts memory barriers on architectures that require them
655 * (which is most of them), and also prevents the compiler from
656 * reordering the code that initializes the structure after the pointer
657 * assignment. More importantly, this call documents which pointers
658 * will be dereferenced by RCU read-side code.
660 * In some special cases, you may use RCU_INIT_POINTER() instead
661 * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due
662 * to the fact that it does not constrain either the CPU or the compiler.
663 * That said, using RCU_INIT_POINTER() when you should have used
664 * rcu_assign_pointer() is a very bad thing that results in
665 * impossible-to-diagnose memory corruption. So please be careful.
666 * See the RCU_INIT_POINTER() comment header for details.
668 * Note that rcu_assign_pointer() evaluates each of its arguments only
669 * once, appearances notwithstanding. One of the "extra" evaluations
670 * is in typeof() and the other visible only to sparse (__CHECKER__),
671 * neither of which actually execute the argument. As with most cpp
672 * macros, this execute-arguments-only-once property is important, so
673 * please be careful when making changes to rcu_assign_pointer() and the
674 * other macros that it invokes.
676 #define rcu_assign_pointer(p, v) smp_store_release(&p, RCU_INITIALIZER(v))
679 * rcu_access_pointer() - fetch RCU pointer with no dereferencing
680 * @p: The pointer to read
682 * Return the value of the specified RCU-protected pointer, but omit the
683 * smp_read_barrier_depends() and keep the READ_ONCE(). This is useful
684 * when the value of this pointer is accessed, but the pointer is not
685 * dereferenced, for example, when testing an RCU-protected pointer against
686 * NULL. Although rcu_access_pointer() may also be used in cases where
687 * update-side locks prevent the value of the pointer from changing, you
688 * should instead use rcu_dereference_protected() for this use case.
690 * It is also permissible to use rcu_access_pointer() when read-side
691 * access to the pointer was removed at least one grace period ago, as
692 * is the case in the context of the RCU callback that is freeing up
693 * the data, or after a synchronize_rcu() returns. This can be useful
694 * when tearing down multi-linked structures after a grace period
697 #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
700 * rcu_dereference_check() - rcu_dereference with debug checking
701 * @p: The pointer to read, prior to dereferencing
702 * @c: The conditions under which the dereference will take place
704 * Do an rcu_dereference(), but check that the conditions under which the
705 * dereference will take place are correct. Typically the conditions
706 * indicate the various locking conditions that should be held at that
707 * point. The check should return true if the conditions are satisfied.
708 * An implicit check for being in an RCU read-side critical section
709 * (rcu_read_lock()) is included.
713 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
715 * could be used to indicate to lockdep that foo->bar may only be dereferenced
716 * if either rcu_read_lock() is held, or that the lock required to replace
717 * the bar struct at foo->bar is held.
719 * Note that the list of conditions may also include indications of when a lock
720 * need not be held, for example during initialisation or destruction of the
723 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
724 * atomic_read(&foo->usage) == 0);
726 * Inserts memory barriers on architectures that require them
727 * (currently only the Alpha), prevents the compiler from refetching
728 * (and from merging fetches), and, more importantly, documents exactly
729 * which pointers are protected by RCU and checks that the pointer is
730 * annotated as __rcu.
732 #define rcu_dereference_check(p, c) \
733 __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
736 * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
737 * @p: The pointer to read, prior to dereferencing
738 * @c: The conditions under which the dereference will take place
740 * This is the RCU-bh counterpart to rcu_dereference_check().
742 #define rcu_dereference_bh_check(p, c) \
743 __rcu_dereference_check((p), (c) || rcu_read_lock_bh_held(), __rcu)
746 * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
747 * @p: The pointer to read, prior to dereferencing
748 * @c: The conditions under which the dereference will take place
750 * This is the RCU-sched counterpart to rcu_dereference_check().
752 #define rcu_dereference_sched_check(p, c) \
753 __rcu_dereference_check((p), (c) || rcu_read_lock_sched_held(), \
756 #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/
759 * The tracing infrastructure traces RCU (we want that), but unfortunately
760 * some of the RCU checks causes tracing to lock up the system.
762 * The tracing version of rcu_dereference_raw() must not call
763 * rcu_read_lock_held().
765 #define rcu_dereference_raw_notrace(p) __rcu_dereference_check((p), 1, __rcu)
768 * rcu_dereference_protected() - fetch RCU pointer when updates prevented
769 * @p: The pointer to read, prior to dereferencing
770 * @c: The conditions under which the dereference will take place
772 * Return the value of the specified RCU-protected pointer, but omit
773 * both the smp_read_barrier_depends() and the READ_ONCE(). This
774 * is useful in cases where update-side locks prevent the value of the
775 * pointer from changing. Please note that this primitive does -not-
776 * prevent the compiler from repeating this reference or combining it
777 * with other references, so it should not be used without protection
778 * of appropriate locks.
780 * This function is only for update-side use. Using this function
781 * when protected only by rcu_read_lock() will result in infrequent
782 * but very ugly failures.
784 #define rcu_dereference_protected(p, c) \
785 __rcu_dereference_protected((p), (c), __rcu)
789 * rcu_dereference() - fetch RCU-protected pointer for dereferencing
790 * @p: The pointer to read, prior to dereferencing
792 * This is a simple wrapper around rcu_dereference_check().
794 #define rcu_dereference(p) rcu_dereference_check(p, 0)
797 * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
798 * @p: The pointer to read, prior to dereferencing
800 * Makes rcu_dereference_check() do the dirty work.
802 #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
805 * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
806 * @p: The pointer to read, prior to dereferencing
808 * Makes rcu_dereference_check() do the dirty work.
810 #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
813 * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism
814 * @p: The pointer to hand off
816 * This is simply an identity function, but it documents where a pointer
817 * is handed off from RCU to some other synchronization mechanism, for
818 * example, reference counting or locking. In C11, it would map to
819 * kill_dependency(). It could be used as follows:
822 * p = rcu_dereference(gp);
823 * long_lived = is_long_lived(p);
825 * if (!atomic_inc_not_zero(p->refcnt))
826 * long_lived = false;
828 * p = rcu_pointer_handoff(p);
832 #define rcu_pointer_handoff(p) (p)
835 * rcu_read_lock() - mark the beginning of an RCU read-side critical section
837 * When synchronize_rcu() is invoked on one CPU while other CPUs
838 * are within RCU read-side critical sections, then the
839 * synchronize_rcu() is guaranteed to block until after all the other
840 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
841 * on one CPU while other CPUs are within RCU read-side critical
842 * sections, invocation of the corresponding RCU callback is deferred
843 * until after the all the other CPUs exit their critical sections.
845 * Note, however, that RCU callbacks are permitted to run concurrently
846 * with new RCU read-side critical sections. One way that this can happen
847 * is via the following sequence of events: (1) CPU 0 enters an RCU
848 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
849 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
850 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
851 * callback is invoked. This is legal, because the RCU read-side critical
852 * section that was running concurrently with the call_rcu() (and which
853 * therefore might be referencing something that the corresponding RCU
854 * callback would free up) has completed before the corresponding
855 * RCU callback is invoked.
857 * RCU read-side critical sections may be nested. Any deferred actions
858 * will be deferred until the outermost RCU read-side critical section
861 * You can avoid reading and understanding the next paragraph by
862 * following this rule: don't put anything in an rcu_read_lock() RCU
863 * read-side critical section that would block in a !PREEMPT kernel.
864 * But if you want the full story, read on!
866 * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU),
867 * it is illegal to block while in an RCU read-side critical section.
868 * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPT
869 * kernel builds, RCU read-side critical sections may be preempted,
870 * but explicit blocking is illegal. Finally, in preemptible RCU
871 * implementations in real-time (with -rt patchset) kernel builds, RCU
872 * read-side critical sections may be preempted and they may also block, but
873 * only when acquiring spinlocks that are subject to priority inheritance.
875 static inline void rcu_read_lock(void)
879 rcu_lock_acquire(&rcu_lock_map);
880 RCU_LOCKDEP_WARN(!rcu_is_watching(),
881 "rcu_read_lock() used illegally while idle");
885 * So where is rcu_write_lock()? It does not exist, as there is no
886 * way for writers to lock out RCU readers. This is a feature, not
887 * a bug -- this property is what provides RCU's performance benefits.
888 * Of course, writers must coordinate with each other. The normal
889 * spinlock primitives work well for this, but any other technique may be
890 * used as well. RCU does not care how the writers keep out of each
891 * others' way, as long as they do so.
895 * rcu_read_unlock() - marks the end of an RCU read-side critical section.
897 * In most situations, rcu_read_unlock() is immune from deadlock.
898 * However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock()
899 * is responsible for deboosting, which it does via rt_mutex_unlock().
900 * Unfortunately, this function acquires the scheduler's runqueue and
901 * priority-inheritance spinlocks. This means that deadlock could result
902 * if the caller of rcu_read_unlock() already holds one of these locks or
903 * any lock that is ever acquired while holding them; or any lock which
904 * can be taken from interrupt context because rcu_boost()->rt_mutex_lock()
905 * does not disable irqs while taking ->wait_lock.
907 * That said, RCU readers are never priority boosted unless they were
908 * preempted. Therefore, one way to avoid deadlock is to make sure
909 * that preemption never happens within any RCU read-side critical
910 * section whose outermost rcu_read_unlock() is called with one of
911 * rt_mutex_unlock()'s locks held. Such preemption can be avoided in
912 * a number of ways, for example, by invoking preempt_disable() before
913 * critical section's outermost rcu_read_lock().
915 * Given that the set of locks acquired by rt_mutex_unlock() might change
916 * at any time, a somewhat more future-proofed approach is to make sure
917 * that that preemption never happens within any RCU read-side critical
918 * section whose outermost rcu_read_unlock() is called with irqs disabled.
919 * This approach relies on the fact that rt_mutex_unlock() currently only
920 * acquires irq-disabled locks.
922 * The second of these two approaches is best in most situations,
923 * however, the first approach can also be useful, at least to those
924 * developers willing to keep abreast of the set of locks acquired by
927 * See rcu_read_lock() for more information.
929 static inline void rcu_read_unlock(void)
931 RCU_LOCKDEP_WARN(!rcu_is_watching(),
932 "rcu_read_unlock() used illegally while idle");
935 rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
939 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
941 * This is equivalent of rcu_read_lock(), but to be used when updates
942 * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since
943 * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a
944 * softirq handler to be a quiescent state, a process in RCU read-side
945 * critical section must be protected by disabling softirqs. Read-side
946 * critical sections in interrupt context can use just rcu_read_lock(),
947 * though this should at least be commented to avoid confusing people
950 * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
951 * must occur in the same context, for example, it is illegal to invoke
952 * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
953 * was invoked from some other task.
955 static inline void rcu_read_lock_bh(void)
958 #ifdef CONFIG_PREEMPT_RT_FULL
962 rcu_lock_acquire(&rcu_bh_lock_map);
963 RCU_LOCKDEP_WARN(!rcu_is_watching(),
964 "rcu_read_lock_bh() used illegally while idle");
969 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
971 * See rcu_read_lock_bh() for more information.
973 static inline void rcu_read_unlock_bh(void)
975 #ifdef CONFIG_PREEMPT_RT_FULL
978 RCU_LOCKDEP_WARN(!rcu_is_watching(),
979 "rcu_read_unlock_bh() used illegally while idle");
980 rcu_lock_release(&rcu_bh_lock_map);
987 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
989 * This is equivalent of rcu_read_lock(), but to be used when updates
990 * are being done using call_rcu_sched() or synchronize_rcu_sched().
991 * Read-side critical sections can also be introduced by anything that
992 * disables preemption, including local_irq_disable() and friends.
994 * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
995 * must occur in the same context, for example, it is illegal to invoke
996 * rcu_read_unlock_sched() from process context if the matching
997 * rcu_read_lock_sched() was invoked from an NMI handler.
999 static inline void rcu_read_lock_sched(void)
1002 __acquire(RCU_SCHED);
1003 rcu_lock_acquire(&rcu_sched_lock_map);
1004 RCU_LOCKDEP_WARN(!rcu_is_watching(),
1005 "rcu_read_lock_sched() used illegally while idle");
1008 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
1009 static inline notrace void rcu_read_lock_sched_notrace(void)
1011 preempt_disable_notrace();
1012 __acquire(RCU_SCHED);
1016 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
1018 * See rcu_read_lock_sched for more information.
1020 static inline void rcu_read_unlock_sched(void)
1022 RCU_LOCKDEP_WARN(!rcu_is_watching(),
1023 "rcu_read_unlock_sched() used illegally while idle");
1024 rcu_lock_release(&rcu_sched_lock_map);
1025 __release(RCU_SCHED);
1029 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
1030 static inline notrace void rcu_read_unlock_sched_notrace(void)
1032 __release(RCU_SCHED);
1033 preempt_enable_notrace();
1037 * RCU_INIT_POINTER() - initialize an RCU protected pointer
1039 * Initialize an RCU-protected pointer in special cases where readers
1040 * do not need ordering constraints on the CPU or the compiler. These
1041 * special cases are:
1043 * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer -or-
1044 * 2. The caller has taken whatever steps are required to prevent
1045 * RCU readers from concurrently accessing this pointer -or-
1046 * 3. The referenced data structure has already been exposed to
1047 * readers either at compile time or via rcu_assign_pointer() -and-
1048 * a. You have not made -any- reader-visible changes to
1049 * this structure since then -or-
1050 * b. It is OK for readers accessing this structure from its
1051 * new location to see the old state of the structure. (For
1052 * example, the changes were to statistical counters or to
1053 * other state where exact synchronization is not required.)
1055 * Failure to follow these rules governing use of RCU_INIT_POINTER() will
1056 * result in impossible-to-diagnose memory corruption. As in the structures
1057 * will look OK in crash dumps, but any concurrent RCU readers might
1058 * see pre-initialized values of the referenced data structure. So
1059 * please be very careful how you use RCU_INIT_POINTER()!!!
1061 * If you are creating an RCU-protected linked structure that is accessed
1062 * by a single external-to-structure RCU-protected pointer, then you may
1063 * use RCU_INIT_POINTER() to initialize the internal RCU-protected
1064 * pointers, but you must use rcu_assign_pointer() to initialize the
1065 * external-to-structure pointer -after- you have completely initialized
1066 * the reader-accessible portions of the linked structure.
1068 * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
1069 * ordering guarantees for either the CPU or the compiler.
1071 #define RCU_INIT_POINTER(p, v) \
1073 rcu_dereference_sparse(p, __rcu); \
1074 WRITE_ONCE(p, RCU_INITIALIZER(v)); \
1078 * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
1080 * GCC-style initialization for an RCU-protected pointer in a structure field.
1082 #define RCU_POINTER_INITIALIZER(p, v) \
1083 .p = RCU_INITIALIZER(v)
1086 * Does the specified offset indicate that the corresponding rcu_head
1087 * structure can be handled by kfree_rcu()?
1089 #define __is_kfree_rcu_offset(offset) ((offset) < 4096)
1092 * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain.
1094 #define __kfree_rcu(head, offset) \
1096 BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \
1097 kfree_call_rcu(head, (rcu_callback_t)(unsigned long)(offset)); \
1101 * kfree_rcu() - kfree an object after a grace period.
1102 * @ptr: pointer to kfree
1103 * @rcu_head: the name of the struct rcu_head within the type of @ptr.
1105 * Many rcu callbacks functions just call kfree() on the base structure.
1106 * These functions are trivial, but their size adds up, and furthermore
1107 * when they are used in a kernel module, that module must invoke the
1108 * high-latency rcu_barrier() function at module-unload time.
1110 * The kfree_rcu() function handles this issue. Rather than encoding a
1111 * function address in the embedded rcu_head structure, kfree_rcu() instead
1112 * encodes the offset of the rcu_head structure within the base structure.
1113 * Because the functions are not allowed in the low-order 4096 bytes of
1114 * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
1115 * If the offset is larger than 4095 bytes, a compile-time error will
1116 * be generated in __kfree_rcu(). If this error is triggered, you can
1117 * either fall back to use of call_rcu() or rearrange the structure to
1118 * position the rcu_head structure into the first 4096 bytes.
1120 * Note that the allowable offset might decrease in the future, for example,
1121 * to allow something like kmem_cache_free_rcu().
1123 * The BUILD_BUG_ON check must not involve any function calls, hence the
1124 * checks are done in macros here.
1126 #define kfree_rcu(ptr, rcu_head) \
1127 __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
1129 #ifdef CONFIG_TINY_RCU
1130 static inline int rcu_needs_cpu(u64 basemono, u64 *nextevt)
1132 *nextevt = KTIME_MAX;
1135 #endif /* #ifdef CONFIG_TINY_RCU */
1137 #if defined(CONFIG_RCU_NOCB_CPU_ALL)
1138 static inline bool rcu_is_nocb_cpu(int cpu) { return true; }
1139 #elif defined(CONFIG_RCU_NOCB_CPU)
1140 bool rcu_is_nocb_cpu(int cpu);
1142 static inline bool rcu_is_nocb_cpu(int cpu) { return false; }
1146 /* Only for use by adaptive-ticks code. */
1147 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
1148 bool rcu_sys_is_idle(void);
1149 void rcu_sysidle_force_exit(void);
1150 #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
1152 static inline bool rcu_sys_is_idle(void)
1157 static inline void rcu_sysidle_force_exit(void)
1161 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
1164 #endif /* __LINUX_RCUPDATE_H */