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1/* SPDX-License-Identifier: GPL-2.0+ */
2/*
3 * Read-Copy Update mechanism for mutual exclusion
4 *
5 * Copyright IBM Corporation, 2001
6 *
7 * Author: Dipankar Sarma <dipankar@in.ibm.com>
8 *
9 * Based on the original work by Paul McKenney <paulmck@vnet.ibm.com>
10 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
11 * Papers:
12 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
13 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
14 *
15 * For detailed explanation of Read-Copy Update mechanism see -
16 * http://lse.sourceforge.net/locking/rcupdate.html
17 *
18 */
19
20#ifndef __LINUX_RCUPDATE_H
21#define __LINUX_RCUPDATE_H
22
23#include <linux/types.h>
24#include <linux/compiler.h>
25#include <linux/atomic.h>
26#include <linux/irqflags.h>
27#include <linux/sched.h>
28#include <linux/bottom_half.h>
29#include <linux/lockdep.h>
30#include <linux/cleanup.h>
31#include <asm/processor.h>
32#include <linux/context_tracking_irq.h>
33
34token_context_lock(RCU, __reentrant_ctx_lock);
35token_context_lock_instance(RCU, RCU_SCHED);
36token_context_lock_instance(RCU, RCU_BH);
37
38/*
39 * A convenience macro that can be used for RCU-protected globals or struct
40 * members; adds type qualifier __rcu, and also enforces __guarded_by(RCU).
41 */
42#define __rcu_guarded __rcu __guarded_by(RCU)
43
44#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))
45#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b))
46
47#define RCU_SEQ_CTR_SHIFT 2
48#define RCU_SEQ_STATE_MASK ((1 << RCU_SEQ_CTR_SHIFT) - 1)
49
50/* Exported common interfaces */
51void call_rcu(struct rcu_head *head, rcu_callback_t func);
52void rcu_barrier_tasks(void);
53void synchronize_rcu(void);
54
55struct rcu_gp_oldstate;
56unsigned long get_completed_synchronize_rcu(void);
57void get_completed_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp);
58
59// Maximum number of unsigned long values corresponding to
60// not-yet-completed RCU grace periods.
61#define NUM_ACTIVE_RCU_POLL_OLDSTATE 2
62
63/**
64 * same_state_synchronize_rcu - Are two old-state values identical?
65 * @oldstate1: First old-state value.
66 * @oldstate2: Second old-state value.
67 *
68 * The two old-state values must have been obtained from either
69 * get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or
70 * get_completed_synchronize_rcu(). Returns @true if the two values are
71 * identical and @false otherwise. This allows structures whose lifetimes
72 * are tracked by old-state values to push these values to a list header,
73 * allowing those structures to be slightly smaller.
74 */
75static inline bool same_state_synchronize_rcu(unsigned long oldstate1, unsigned long oldstate2)
76{
77 return oldstate1 == oldstate2;
78}
79
80#ifdef CONFIG_PREEMPT_RCU
81
82void __rcu_read_lock(void);
83void __rcu_read_unlock(void);
84
85/*
86 * Defined as a macro as it is a very low level header included from
87 * areas that don't even know about current. This gives the rcu_read_lock()
88 * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
89 * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
90 */
91#define rcu_preempt_depth() READ_ONCE(current->rcu_read_lock_nesting)
92
93#else /* #ifdef CONFIG_PREEMPT_RCU */
94
95#ifdef CONFIG_TINY_RCU
96#define rcu_read_unlock_strict() do { } while (0)
97#else
98void rcu_read_unlock_strict(void);
99#endif
100
101static inline void __rcu_read_lock(void)
102{
103 preempt_disable();
104}
105
106static inline void __rcu_read_unlock(void)
107{
108 if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
109 rcu_read_unlock_strict();
110 preempt_enable();
111}
112
113static inline int rcu_preempt_depth(void)
114{
115 return 0;
116}
117
118#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
119
120#ifdef CONFIG_RCU_LAZY
121void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func);
122#else
123static inline void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func)
124{
125 call_rcu(head, func);
126}
127#endif
128
129/* Internal to kernel */
130void rcu_init(void);
131extern int rcu_scheduler_active;
132void rcu_sched_clock_irq(int user);
133
134#ifdef CONFIG_RCU_STALL_COMMON
135void rcu_sysrq_start(void);
136void rcu_sysrq_end(void);
137#else /* #ifdef CONFIG_RCU_STALL_COMMON */
138static inline void rcu_sysrq_start(void) { }
139static inline void rcu_sysrq_end(void) { }
140#endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
141
142#if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_VIRT_XFER_TO_GUEST_WORK))
143void rcu_irq_work_resched(void);
144#else
145static __always_inline void rcu_irq_work_resched(void) { }
146#endif
147
148#ifdef CONFIG_RCU_NOCB_CPU
149void rcu_init_nohz(void);
150int rcu_nocb_cpu_offload(int cpu);
151int rcu_nocb_cpu_deoffload(int cpu);
152void rcu_nocb_flush_deferred_wakeup(void);
153
154#define RCU_NOCB_LOCKDEP_WARN(c, s) RCU_LOCKDEP_WARN(c, s)
155
156#else /* #ifdef CONFIG_RCU_NOCB_CPU */
157
158static inline void rcu_init_nohz(void) { }
159static inline int rcu_nocb_cpu_offload(int cpu) { return -EINVAL; }
160static inline int rcu_nocb_cpu_deoffload(int cpu) { return 0; }
161static inline void rcu_nocb_flush_deferred_wakeup(void) { }
162
163#define RCU_NOCB_LOCKDEP_WARN(c, s)
164
165#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
166
167/*
168 * Note a quasi-voluntary context switch for RCU-tasks's benefit.
169 * This is a macro rather than an inline function to avoid #include hell.
170 */
171#ifdef CONFIG_TASKS_RCU_GENERIC
172
173# ifdef CONFIG_TASKS_RCU
174# define rcu_tasks_classic_qs(t, preempt) \
175 do { \
176 if (!(preempt) && READ_ONCE((t)->rcu_tasks_holdout)) \
177 WRITE_ONCE((t)->rcu_tasks_holdout, false); \
178 } while (0)
179void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
180void synchronize_rcu_tasks(void);
181void rcu_tasks_torture_stats_print(char *tt, char *tf);
182# else
183# define rcu_tasks_classic_qs(t, preempt) do { } while (0)
184# define call_rcu_tasks call_rcu
185# define synchronize_rcu_tasks synchronize_rcu
186# endif
187
188#define rcu_tasks_qs(t, preempt) rcu_tasks_classic_qs((t), (preempt))
189
190# ifdef CONFIG_TASKS_RUDE_RCU
191void synchronize_rcu_tasks_rude(void);
192void rcu_tasks_rude_torture_stats_print(char *tt, char *tf);
193# endif
194
195#define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t, false)
196void exit_tasks_rcu_start(void);
197void exit_tasks_rcu_finish(void);
198#else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
199#define rcu_tasks_classic_qs(t, preempt) do { } while (0)
200#define rcu_tasks_qs(t, preempt) do { } while (0)
201#define rcu_note_voluntary_context_switch(t) do { } while (0)
202#define call_rcu_tasks call_rcu
203#define synchronize_rcu_tasks synchronize_rcu
204static inline void exit_tasks_rcu_start(void) { }
205static inline void exit_tasks_rcu_finish(void) { }
206#endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */
207
208/**
209 * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU
210 *
211 * This macro resembles cond_resched(), except that it is defined to
212 * report potential quiescent states to RCU-tasks even if the cond_resched()
213 * machinery were to be shut off, as some advocate for PREEMPTION kernels.
214 */
215#define cond_resched_tasks_rcu_qs() \
216do { \
217 rcu_tasks_qs(current, false); \
218 cond_resched(); \
219} while (0)
220
221/**
222 * rcu_softirq_qs_periodic - Report RCU and RCU-Tasks quiescent states
223 * @old_ts: jiffies at start of processing.
224 *
225 * This helper is for long-running softirq handlers, such as NAPI threads in
226 * networking. The caller should initialize the variable passed in as @old_ts
227 * at the beginning of the softirq handler. When invoked frequently, this macro
228 * will invoke rcu_softirq_qs() every 100 milliseconds thereafter, which will
229 * provide both RCU and RCU-Tasks quiescent states. Note that this macro
230 * modifies its old_ts argument.
231 *
232 * Because regions of code that have disabled softirq act as RCU read-side
233 * critical sections, this macro should be invoked with softirq (and
234 * preemption) enabled.
235 *
236 * The macro is not needed when CONFIG_PREEMPT_RT is defined. RT kernels would
237 * have more chance to invoke schedule() calls and provide necessary quiescent
238 * states. As a contrast, calling cond_resched() only won't achieve the same
239 * effect because cond_resched() does not provide RCU-Tasks quiescent states.
240 */
241#define rcu_softirq_qs_periodic(old_ts) \
242do { \
243 if (!IS_ENABLED(CONFIG_PREEMPT_RT) && \
244 time_after(jiffies, (old_ts) + HZ / 10)) { \
245 preempt_disable(); \
246 rcu_softirq_qs(); \
247 preempt_enable(); \
248 (old_ts) = jiffies; \
249 } \
250} while (0)
251
252/*
253 * Infrastructure to implement the synchronize_() primitives in
254 * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
255 */
256
257#if defined(CONFIG_TREE_RCU)
258#include <linux/rcutree.h>
259#elif defined(CONFIG_TINY_RCU)
260#include <linux/rcutiny.h>
261#else
262#error "Unknown RCU implementation specified to kernel configuration"
263#endif
264
265/*
266 * The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls
267 * are needed for dynamic initialization and destruction of rcu_head
268 * on the stack, and init_rcu_head()/destroy_rcu_head() are needed for
269 * dynamic initialization and destruction of statically allocated rcu_head
270 * structures. However, rcu_head structures allocated dynamically in the
271 * heap don't need any initialization.
272 */
273#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
274void init_rcu_head(struct rcu_head *head);
275void destroy_rcu_head(struct rcu_head *head);
276void init_rcu_head_on_stack(struct rcu_head *head);
277void destroy_rcu_head_on_stack(struct rcu_head *head);
278#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
279static inline void init_rcu_head(struct rcu_head *head) { }
280static inline void destroy_rcu_head(struct rcu_head *head) { }
281static inline void init_rcu_head_on_stack(struct rcu_head *head) { }
282static inline void destroy_rcu_head_on_stack(struct rcu_head *head) { }
283#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
284
285#if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
286bool rcu_lockdep_current_cpu_online(void);
287#else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
288static inline bool rcu_lockdep_current_cpu_online(void) { return true; }
289#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
290
291extern struct lockdep_map rcu_lock_map;
292extern struct lockdep_map rcu_bh_lock_map;
293extern struct lockdep_map rcu_sched_lock_map;
294extern struct lockdep_map rcu_callback_map;
295
296#ifdef CONFIG_DEBUG_LOCK_ALLOC
297
298static inline void rcu_lock_acquire(struct lockdep_map *map)
299{
300 lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
301}
302
303static inline void rcu_try_lock_acquire(struct lockdep_map *map)
304{
305 lock_acquire(map, 0, 1, 2, 0, NULL, _THIS_IP_);
306}
307
308static inline void rcu_lock_release(struct lockdep_map *map)
309{
310 lock_release(map, _THIS_IP_);
311}
312
313int debug_lockdep_rcu_enabled(void);
314int rcu_read_lock_held(void);
315int rcu_read_lock_bh_held(void);
316int rcu_read_lock_sched_held(void);
317int rcu_read_lock_any_held(void);
318
319#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
320
321# define rcu_lock_acquire(a) do { } while (0)
322# define rcu_try_lock_acquire(a) do { } while (0)
323# define rcu_lock_release(a) do { } while (0)
324
325static inline int rcu_read_lock_held(void)
326{
327 return 1;
328}
329
330static inline int rcu_read_lock_bh_held(void)
331{
332 return 1;
333}
334
335static inline int rcu_read_lock_sched_held(void)
336{
337 return !preemptible();
338}
339
340static inline int rcu_read_lock_any_held(void)
341{
342 return !preemptible();
343}
344
345static inline int debug_lockdep_rcu_enabled(void)
346{
347 return 0;
348}
349
350#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
351
352#ifdef CONFIG_PROVE_RCU
353
354/**
355 * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met
356 * @c: condition to check
357 * @s: informative message
358 *
359 * This checks debug_lockdep_rcu_enabled() before checking (c) to
360 * prevent early boot splats due to lockdep not yet being initialized,
361 * and rechecks it after checking (c) to prevent false-positive splats
362 * due to races with lockdep being disabled. See commit 3066820034b5dd
363 * ("rcu: Reject RCU_LOCKDEP_WARN() false positives") for more detail.
364 */
365#define RCU_LOCKDEP_WARN(c, s) \
366 do { \
367 static bool __section(".data..unlikely") __warned; \
368 if (debug_lockdep_rcu_enabled() && (c) && \
369 debug_lockdep_rcu_enabled() && !__warned) { \
370 __warned = true; \
371 lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
372 } \
373 } while (0)
374
375#ifndef CONFIG_PREEMPT_RCU
376static inline void rcu_preempt_sleep_check(void)
377{
378 RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
379 "Illegal context switch in RCU read-side critical section");
380}
381#else // #ifndef CONFIG_PREEMPT_RCU
382static inline void rcu_preempt_sleep_check(void) { }
383#endif // #else // #ifndef CONFIG_PREEMPT_RCU
384
385#define rcu_sleep_check() \
386 do { \
387 rcu_preempt_sleep_check(); \
388 if (!IS_ENABLED(CONFIG_PREEMPT_RT)) \
389 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map), \
390 "Illegal context switch in RCU-bh read-side critical section"); \
391 RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), \
392 "Illegal context switch in RCU-sched read-side critical section"); \
393 } while (0)
394
395// See RCU_LOCKDEP_WARN() for an explanation of the double call to
396// debug_lockdep_rcu_enabled().
397static __always_inline bool lockdep_assert_rcu_helper(bool c, const struct __ctx_lock_RCU *ctx)
398 __assumes_shared_ctx_lock(RCU) __assumes_shared_ctx_lock(ctx)
399{
400 return debug_lockdep_rcu_enabled() &&
401 (c || !rcu_is_watching() || !rcu_lockdep_current_cpu_online()) &&
402 debug_lockdep_rcu_enabled();
403}
404
405/**
406 * lockdep_assert_in_rcu_read_lock - WARN if not protected by rcu_read_lock()
407 *
408 * Splats if lockdep is enabled and there is no rcu_read_lock() in effect.
409 */
410#define lockdep_assert_in_rcu_read_lock() \
411 WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_lock_map), RCU))
412
413/**
414 * lockdep_assert_in_rcu_read_lock_bh - WARN if not protected by rcu_read_lock_bh()
415 *
416 * Splats if lockdep is enabled and there is no rcu_read_lock_bh() in effect.
417 * Note that local_bh_disable() and friends do not suffice here, instead an
418 * actual rcu_read_lock_bh() is required.
419 */
420#define lockdep_assert_in_rcu_read_lock_bh() \
421 WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_bh_lock_map), RCU_BH))
422
423/**
424 * lockdep_assert_in_rcu_read_lock_sched - WARN if not protected by rcu_read_lock_sched()
425 *
426 * Splats if lockdep is enabled and there is no rcu_read_lock_sched()
427 * in effect. Note that preempt_disable() and friends do not suffice here,
428 * instead an actual rcu_read_lock_sched() is required.
429 */
430#define lockdep_assert_in_rcu_read_lock_sched() \
431 WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_sched_lock_map), RCU_SCHED))
432
433/**
434 * lockdep_assert_in_rcu_reader - WARN if not within some type of RCU reader
435 *
436 * Splats if lockdep is enabled and there is no RCU reader of any
437 * type in effect. Note that regions of code protected by things like
438 * preempt_disable, local_bh_disable(), and local_irq_disable() all qualify
439 * as RCU readers.
440 *
441 * Note that this will never trigger in PREEMPT_NONE or PREEMPT_VOLUNTARY
442 * kernels that are not also built with PREEMPT_COUNT. But if you have
443 * lockdep enabled, you might as well also enable PREEMPT_COUNT.
444 */
445#define lockdep_assert_in_rcu_reader() \
446 WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_lock_map) && \
447 !lock_is_held(&rcu_bh_lock_map) && \
448 !lock_is_held(&rcu_sched_lock_map) && \
449 preemptible(), RCU))
450
451#else /* #ifdef CONFIG_PROVE_RCU */
452
453#define RCU_LOCKDEP_WARN(c, s) do { } while (0 && (c))
454#define rcu_sleep_check() do { } while (0)
455
456#define lockdep_assert_in_rcu_read_lock() __assume_shared_ctx_lock(RCU)
457#define lockdep_assert_in_rcu_read_lock_bh() __assume_shared_ctx_lock(RCU_BH)
458#define lockdep_assert_in_rcu_read_lock_sched() __assume_shared_ctx_lock(RCU_SCHED)
459#define lockdep_assert_in_rcu_reader() __assume_shared_ctx_lock(RCU)
460
461#endif /* #else #ifdef CONFIG_PROVE_RCU */
462
463/*
464 * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
465 * and rcu_assign_pointer(). Some of these could be folded into their
466 * callers, but they are left separate in order to ease introduction of
467 * multiple pointers markings to match different RCU implementations
468 * (e.g., __srcu), should this make sense in the future.
469 */
470
471#ifdef __CHECKER__
472#define rcu_check_sparse(p, space) \
473 ((void)(((typeof(*p) space *)p) == p))
474#else /* #ifdef __CHECKER__ */
475#define rcu_check_sparse(p, space)
476#endif /* #else #ifdef __CHECKER__ */
477
478#define __unrcu_pointer(p, local) \
479context_unsafe( \
480 typeof(*p) *local = (typeof(*p) *__force)(p); \
481 rcu_check_sparse(p, __rcu); \
482 ((typeof(*p) __force __kernel *)(local)) \
483)
484/**
485 * unrcu_pointer - mark a pointer as not being RCU protected
486 * @p: pointer needing to lose its __rcu property
487 *
488 * Converts @p from an __rcu pointer to a __kernel pointer.
489 * This allows an __rcu pointer to be used with xchg() and friends.
490 */
491#define unrcu_pointer(p) __unrcu_pointer(p, __UNIQUE_ID(rcu))
492
493#define __rcu_access_pointer(p, local, space) \
494({ \
495 typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \
496 rcu_check_sparse(p, space); \
497 ((typeof(*p) __force __kernel *)(local)); \
498})
499#define __rcu_dereference_check(p, local, c, space) \
500({ \
501 /* Dependency order vs. p above. */ \
502 typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \
503 RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
504 rcu_check_sparse(p, space); \
505 ((typeof(*p) __force __kernel *)(local)); \
506})
507#define __rcu_dereference_protected(p, local, c, space) \
508({ \
509 RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
510 rcu_check_sparse(p, space); \
511 ((typeof(*p) __force __kernel *)(p)); \
512})
513#define __rcu_dereference_raw(p, local) \
514({ \
515 /* Dependency order vs. p above. */ \
516 typeof(p) local = READ_ONCE(p); \
517 ((typeof(*p) __force __kernel *)(local)); \
518})
519#define rcu_dereference_raw(p) __rcu_dereference_raw(p, __UNIQUE_ID(rcu))
520
521/**
522 * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
523 * @v: The value to statically initialize with.
524 */
525#define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
526
527/**
528 * rcu_assign_pointer() - assign to RCU-protected pointer
529 * @p: pointer to assign to
530 * @v: value to assign (publish)
531 *
532 * Assigns the specified value to the specified RCU-protected
533 * pointer, ensuring that any concurrent RCU readers will see
534 * any prior initialization.
535 *
536 * Inserts memory barriers on architectures that require them
537 * (which is most of them), and also prevents the compiler from
538 * reordering the code that initializes the structure after the pointer
539 * assignment. More importantly, this call documents which pointers
540 * will be dereferenced by RCU read-side code.
541 *
542 * In some special cases, you may use RCU_INIT_POINTER() instead
543 * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due
544 * to the fact that it does not constrain either the CPU or the compiler.
545 * That said, using RCU_INIT_POINTER() when you should have used
546 * rcu_assign_pointer() is a very bad thing that results in
547 * impossible-to-diagnose memory corruption. So please be careful.
548 * See the RCU_INIT_POINTER() comment header for details.
549 *
550 * Note that rcu_assign_pointer() evaluates each of its arguments only
551 * once, appearances notwithstanding. One of the "extra" evaluations
552 * is in typeof() and the other visible only to sparse (__CHECKER__),
553 * neither of which actually execute the argument. As with most cpp
554 * macros, this execute-arguments-only-once property is important, so
555 * please be careful when making changes to rcu_assign_pointer() and the
556 * other macros that it invokes.
557 */
558#define rcu_assign_pointer(p, v) \
559context_unsafe( \
560 uintptr_t _r_a_p__v = (uintptr_t)(v); \
561 rcu_check_sparse(p, __rcu); \
562 \
563 if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \
564 WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \
565 else \
566 smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \
567)
568
569/**
570 * rcu_replace_pointer() - replace an RCU pointer, returning its old value
571 * @rcu_ptr: RCU pointer, whose old value is returned
572 * @ptr: regular pointer
573 * @c: the lockdep conditions under which the dereference will take place
574 *
575 * Perform a replacement, where @rcu_ptr is an RCU-annotated
576 * pointer and @c is the lockdep argument that is passed to the
577 * rcu_dereference_protected() call used to read that pointer. The old
578 * value of @rcu_ptr is returned, and @rcu_ptr is set to @ptr.
579 */
580#define rcu_replace_pointer(rcu_ptr, ptr, c) \
581({ \
582 typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c)); \
583 rcu_assign_pointer((rcu_ptr), (ptr)); \
584 __tmp; \
585})
586
587/**
588 * rcu_access_pointer() - fetch RCU pointer with no dereferencing
589 * @p: The pointer to read
590 *
591 * Return the value of the specified RCU-protected pointer, but omit the
592 * lockdep checks for being in an RCU read-side critical section. This is
593 * useful when the value of this pointer is accessed, but the pointer is
594 * not dereferenced, for example, when testing an RCU-protected pointer
595 * against NULL. Although rcu_access_pointer() may also be used in cases
596 * where update-side locks prevent the value of the pointer from changing,
597 * you should instead use rcu_dereference_protected() for this use case.
598 * Within an RCU read-side critical section, there is little reason to
599 * use rcu_access_pointer().
600 *
601 * It is usually best to test the rcu_access_pointer() return value
602 * directly in order to avoid accidental dereferences being introduced
603 * by later inattentive changes. In other words, assigning the
604 * rcu_access_pointer() return value to a local variable results in an
605 * accident waiting to happen.
606 *
607 * It is also permissible to use rcu_access_pointer() when read-side
608 * access to the pointer was removed at least one grace period ago, as is
609 * the case in the context of the RCU callback that is freeing up the data,
610 * or after a synchronize_rcu() returns. This can be useful when tearing
611 * down multi-linked structures after a grace period has elapsed. However,
612 * rcu_dereference_protected() is normally preferred for this use case.
613 */
614#define rcu_access_pointer(p) __rcu_access_pointer((p), __UNIQUE_ID(rcu), __rcu)
615
616/**
617 * rcu_dereference_check() - rcu_dereference with debug checking
618 * @p: The pointer to read, prior to dereferencing
619 * @c: The conditions under which the dereference will take place
620 *
621 * Do an rcu_dereference(), but check that the conditions under which the
622 * dereference will take place are correct. Typically the conditions
623 * indicate the various locking conditions that should be held at that
624 * point. The check should return true if the conditions are satisfied.
625 * An implicit check for being in an RCU read-side critical section
626 * (rcu_read_lock()) is included.
627 *
628 * For example:
629 *
630 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
631 *
632 * could be used to indicate to lockdep that foo->bar may only be dereferenced
633 * if either rcu_read_lock() is held, or that the lock required to replace
634 * the bar struct at foo->bar is held.
635 *
636 * Note that the list of conditions may also include indications of when a lock
637 * need not be held, for example during initialisation or destruction of the
638 * target struct:
639 *
640 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
641 * atomic_read(&foo->usage) == 0);
642 *
643 * Inserts memory barriers on architectures that require them
644 * (currently only the Alpha), prevents the compiler from refetching
645 * (and from merging fetches), and, more importantly, documents exactly
646 * which pointers are protected by RCU and checks that the pointer is
647 * annotated as __rcu.
648 */
649#define rcu_dereference_check(p, c) \
650 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
651 (c) || rcu_read_lock_held(), __rcu)
652
653/**
654 * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
655 * @p: The pointer to read, prior to dereferencing
656 * @c: The conditions under which the dereference will take place
657 *
658 * This is the RCU-bh counterpart to rcu_dereference_check(). However,
659 * please note that starting in v5.0 kernels, vanilla RCU grace periods
660 * wait for local_bh_disable() regions of code in addition to regions of
661 * code demarked by rcu_read_lock() and rcu_read_unlock(). This means
662 * that synchronize_rcu(), call_rcu, and friends all take not only
663 * rcu_read_lock() but also rcu_read_lock_bh() into account.
664 */
665#define rcu_dereference_bh_check(p, c) \
666 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
667 (c) || rcu_read_lock_bh_held(), __rcu)
668
669/**
670 * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
671 * @p: The pointer to read, prior to dereferencing
672 * @c: The conditions under which the dereference will take place
673 *
674 * This is the RCU-sched counterpart to rcu_dereference_check().
675 * However, please note that starting in v5.0 kernels, vanilla RCU grace
676 * periods wait for preempt_disable() regions of code in addition to
677 * regions of code demarked by rcu_read_lock() and rcu_read_unlock().
678 * This means that synchronize_rcu(), call_rcu, and friends all take not
679 * only rcu_read_lock() but also rcu_read_lock_sched() into account.
680 */
681#define rcu_dereference_sched_check(p, c) \
682 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
683 (c) || rcu_read_lock_sched_held(), \
684 __rcu)
685
686/**
687 * rcu_dereference_all_check() - rcu_dereference_all with debug checking
688 * @p: The pointer to read, prior to dereferencing
689 * @c: The conditions under which the dereference will take place
690 *
691 * This is similar to rcu_dereference_check(), but allows protection
692 * by all forms of vanilla RCU readers, including preemption disabled,
693 * bh-disabled, and interrupt-disabled regions of code. Note that "vanilla
694 * RCU" excludes SRCU and the various Tasks RCU flavors. Please note
695 * that this macro should not be backported to any Linux-kernel version
696 * preceding v5.0 due to changes in synchronize_rcu() semantics prior
697 * to that version.
698 */
699#define rcu_dereference_all_check(p, c) \
700 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
701 (c) || rcu_read_lock_any_held(), \
702 __rcu)
703
704/*
705 * The tracing infrastructure traces RCU (we want that), but unfortunately
706 * some of the RCU checks causes tracing to lock up the system.
707 *
708 * The no-tracing version of rcu_dereference_raw() must not call
709 * rcu_read_lock_held().
710 */
711#define rcu_dereference_raw_check(p) \
712 __rcu_dereference_check((p), __UNIQUE_ID(rcu), 1, __rcu)
713
714/**
715 * rcu_dereference_protected() - fetch RCU pointer when updates prevented
716 * @p: The pointer to read, prior to dereferencing
717 * @c: The conditions under which the dereference will take place
718 *
719 * Return the value of the specified RCU-protected pointer, but omit
720 * the READ_ONCE(). This is useful in cases where update-side locks
721 * prevent the value of the pointer from changing. Please note that this
722 * primitive does *not* prevent the compiler from repeating this reference
723 * or combining it with other references, so it should not be used without
724 * protection of appropriate locks.
725 *
726 * This function is only for update-side use. Using this function
727 * when protected only by rcu_read_lock() will result in infrequent
728 * but very ugly failures.
729 */
730#define rcu_dereference_protected(p, c) \
731 __rcu_dereference_protected((p), __UNIQUE_ID(rcu), (c), __rcu)
732
733
734/**
735 * rcu_dereference() - fetch RCU-protected pointer for dereferencing
736 * @p: The pointer to read, prior to dereferencing
737 *
738 * This is a simple wrapper around rcu_dereference_check().
739 */
740#define rcu_dereference(p) rcu_dereference_check(p, 0)
741
742/**
743 * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
744 * @p: The pointer to read, prior to dereferencing
745 *
746 * Makes rcu_dereference_check() do the dirty work.
747 */
748#define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
749
750/**
751 * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
752 * @p: The pointer to read, prior to dereferencing
753 *
754 * Makes rcu_dereference_check() do the dirty work.
755 */
756#define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
757
758/**
759 * rcu_dereference_all() - fetch RCU-all-protected pointer for dereferencing
760 * @p: The pointer to read, prior to dereferencing
761 *
762 * Makes rcu_dereference_check() do the dirty work.
763 */
764#define rcu_dereference_all(p) rcu_dereference_all_check(p, 0)
765
766/**
767 * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism
768 * @p: The pointer to hand off
769 *
770 * This is simply an identity function, but it documents where a pointer
771 * is handed off from RCU to some other synchronization mechanism, for
772 * example, reference counting or locking. In C11, it would map to
773 * kill_dependency(). It could be used as follows::
774 *
775 * rcu_read_lock();
776 * p = rcu_dereference(gp);
777 * long_lived = is_long_lived(p);
778 * if (long_lived) {
779 * if (!atomic_inc_not_zero(p->refcnt))
780 * long_lived = false;
781 * else
782 * p = rcu_pointer_handoff(p);
783 * }
784 * rcu_read_unlock();
785 */
786#define rcu_pointer_handoff(p) (p)
787
788/**
789 * rcu_read_lock() - mark the beginning of an RCU read-side critical section
790 *
791 * When synchronize_rcu() is invoked on one CPU while other CPUs
792 * are within RCU read-side critical sections, then the
793 * synchronize_rcu() is guaranteed to block until after all the other
794 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
795 * on one CPU while other CPUs are within RCU read-side critical
796 * sections, invocation of the corresponding RCU callback is deferred
797 * until after the all the other CPUs exit their critical sections.
798 *
799 * Both synchronize_rcu() and call_rcu() also wait for regions of code
800 * with preemption disabled, including regions of code with interrupts or
801 * softirqs disabled.
802 *
803 * Note, however, that RCU callbacks are permitted to run concurrently
804 * with new RCU read-side critical sections. One way that this can happen
805 * is via the following sequence of events: (1) CPU 0 enters an RCU
806 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
807 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
808 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
809 * callback is invoked. This is legal, because the RCU read-side critical
810 * section that was running concurrently with the call_rcu() (and which
811 * therefore might be referencing something that the corresponding RCU
812 * callback would free up) has completed before the corresponding
813 * RCU callback is invoked.
814 *
815 * RCU read-side critical sections may be nested. Any deferred actions
816 * will be deferred until the outermost RCU read-side critical section
817 * completes.
818 *
819 * You can avoid reading and understanding the next paragraph by
820 * following this rule: don't put anything in an rcu_read_lock() RCU
821 * read-side critical section that would block in a !PREEMPTION kernel.
822 * But if you want the full story, read on!
823 *
824 * In non-preemptible RCU implementations (pure TREE_RCU and TINY_RCU),
825 * it is illegal to block while in an RCU read-side critical section.
826 * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPTION
827 * kernel builds, RCU read-side critical sections may be preempted,
828 * but explicit blocking is illegal. Finally, in preemptible RCU
829 * implementations in real-time (with -rt patchset) kernel builds, RCU
830 * read-side critical sections may be preempted and they may also block, but
831 * only when acquiring spinlocks that are subject to priority inheritance.
832 */
833static __always_inline void rcu_read_lock(void)
834 __acquires_shared(RCU)
835{
836 __rcu_read_lock();
837 __acquire_shared(RCU);
838 rcu_lock_acquire(&rcu_lock_map);
839 RCU_LOCKDEP_WARN(!rcu_is_watching(),
840 "rcu_read_lock() used illegally while idle");
841}
842
843/*
844 * So where is rcu_write_lock()? It does not exist, as there is no
845 * way for writers to lock out RCU readers. This is a feature, not
846 * a bug -- this property is what provides RCU's performance benefits.
847 * Of course, writers must coordinate with each other. The normal
848 * spinlock primitives work well for this, but any other technique may be
849 * used as well. RCU does not care how the writers keep out of each
850 * others' way, as long as they do so.
851 */
852
853/**
854 * rcu_read_unlock() - marks the end of an RCU read-side critical section.
855 *
856 * In almost all situations, rcu_read_unlock() is immune from deadlock.
857 * This deadlock immunity also extends to the scheduler's runqueue
858 * and priority-inheritance spinlocks, courtesy of the quiescent-state
859 * deferral that is carried out when rcu_read_unlock() is invoked with
860 * interrupts disabled.
861 *
862 * See rcu_read_lock() for more information.
863 */
864static inline void rcu_read_unlock(void)
865 __releases_shared(RCU)
866{
867 RCU_LOCKDEP_WARN(!rcu_is_watching(),
868 "rcu_read_unlock() used illegally while idle");
869 rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
870 __release_shared(RCU);
871 __rcu_read_unlock();
872}
873
874/**
875 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
876 *
877 * This is equivalent to rcu_read_lock(), but also disables softirqs.
878 * Note that anything else that disables softirqs can also serve as an RCU
879 * read-side critical section. However, please note that this equivalence
880 * applies only to v5.0 and later. Before v5.0, rcu_read_lock() and
881 * rcu_read_lock_bh() were unrelated.
882 *
883 * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
884 * must occur in the same context, for example, it is illegal to invoke
885 * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
886 * was invoked from some other task.
887 */
888static inline void rcu_read_lock_bh(void)
889 __acquires_shared(RCU) __acquires_shared(RCU_BH)
890{
891 local_bh_disable();
892 __acquire_shared(RCU);
893 __acquire_shared(RCU_BH);
894 rcu_lock_acquire(&rcu_bh_lock_map);
895 RCU_LOCKDEP_WARN(!rcu_is_watching(),
896 "rcu_read_lock_bh() used illegally while idle");
897}
898
899/**
900 * rcu_read_unlock_bh() - marks the end of a softirq-only RCU critical section
901 *
902 * See rcu_read_lock_bh() for more information.
903 */
904static inline void rcu_read_unlock_bh(void)
905 __releases_shared(RCU) __releases_shared(RCU_BH)
906{
907 RCU_LOCKDEP_WARN(!rcu_is_watching(),
908 "rcu_read_unlock_bh() used illegally while idle");
909 rcu_lock_release(&rcu_bh_lock_map);
910 __release_shared(RCU_BH);
911 __release_shared(RCU);
912 local_bh_enable();
913}
914
915/**
916 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
917 *
918 * This is equivalent to rcu_read_lock(), but also disables preemption.
919 * Read-side critical sections can also be introduced by anything else that
920 * disables preemption, including local_irq_disable() and friends. However,
921 * please note that the equivalence to rcu_read_lock() applies only to
922 * v5.0 and later. Before v5.0, rcu_read_lock() and rcu_read_lock_sched()
923 * were unrelated.
924 *
925 * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
926 * must occur in the same context, for example, it is illegal to invoke
927 * rcu_read_unlock_sched() from process context if the matching
928 * rcu_read_lock_sched() was invoked from an NMI handler.
929 */
930static inline void rcu_read_lock_sched(void)
931 __acquires_shared(RCU) __acquires_shared(RCU_SCHED)
932{
933 preempt_disable();
934 __acquire_shared(RCU);
935 __acquire_shared(RCU_SCHED);
936 rcu_lock_acquire(&rcu_sched_lock_map);
937 RCU_LOCKDEP_WARN(!rcu_is_watching(),
938 "rcu_read_lock_sched() used illegally while idle");
939}
940
941/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
942static inline notrace void rcu_read_lock_sched_notrace(void)
943 __acquires_shared(RCU) __acquires_shared(RCU_SCHED)
944{
945 preempt_disable_notrace();
946 __acquire_shared(RCU);
947 __acquire_shared(RCU_SCHED);
948}
949
950/**
951 * rcu_read_unlock_sched() - marks the end of a RCU-classic critical section
952 *
953 * See rcu_read_lock_sched() for more information.
954 */
955static inline void rcu_read_unlock_sched(void)
956 __releases_shared(RCU) __releases_shared(RCU_SCHED)
957{
958 RCU_LOCKDEP_WARN(!rcu_is_watching(),
959 "rcu_read_unlock_sched() used illegally while idle");
960 rcu_lock_release(&rcu_sched_lock_map);
961 __release_shared(RCU_SCHED);
962 __release_shared(RCU);
963 preempt_enable();
964}
965
966/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
967static inline notrace void rcu_read_unlock_sched_notrace(void)
968 __releases_shared(RCU) __releases_shared(RCU_SCHED)
969{
970 __release_shared(RCU_SCHED);
971 __release_shared(RCU);
972 preempt_enable_notrace();
973}
974
975static __always_inline void rcu_read_lock_dont_migrate(void)
976 __acquires_shared(RCU)
977{
978 if (IS_ENABLED(CONFIG_PREEMPT_RCU))
979 migrate_disable();
980 rcu_read_lock();
981}
982
983static inline void rcu_read_unlock_migrate(void)
984 __releases_shared(RCU)
985{
986 rcu_read_unlock();
987 if (IS_ENABLED(CONFIG_PREEMPT_RCU))
988 migrate_enable();
989}
990
991/**
992 * RCU_INIT_POINTER() - initialize an RCU protected pointer
993 * @p: The pointer to be initialized.
994 * @v: The value to initialized the pointer to.
995 *
996 * Initialize an RCU-protected pointer in special cases where readers
997 * do not need ordering constraints on the CPU or the compiler. These
998 * special cases are:
999 *
1000 * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer *or*
1001 * 2. The caller has taken whatever steps are required to prevent
1002 * RCU readers from concurrently accessing this pointer *or*
1003 * 3. The referenced data structure has already been exposed to
1004 * readers either at compile time or via rcu_assign_pointer() *and*
1005 *
1006 * a. You have not made *any* reader-visible changes to
1007 * this structure since then *or*
1008 * b. It is OK for readers accessing this structure from its
1009 * new location to see the old state of the structure. (For
1010 * example, the changes were to statistical counters or to
1011 * other state where exact synchronization is not required.)
1012 *
1013 * Failure to follow these rules governing use of RCU_INIT_POINTER() will
1014 * result in impossible-to-diagnose memory corruption. As in the structures
1015 * will look OK in crash dumps, but any concurrent RCU readers might
1016 * see pre-initialized values of the referenced data structure. So
1017 * please be very careful how you use RCU_INIT_POINTER()!!!
1018 *
1019 * If you are creating an RCU-protected linked structure that is accessed
1020 * by a single external-to-structure RCU-protected pointer, then you may
1021 * use RCU_INIT_POINTER() to initialize the internal RCU-protected
1022 * pointers, but you must use rcu_assign_pointer() to initialize the
1023 * external-to-structure pointer *after* you have completely initialized
1024 * the reader-accessible portions of the linked structure.
1025 *
1026 * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
1027 * ordering guarantees for either the CPU or the compiler.
1028 */
1029#define RCU_INIT_POINTER(p, v) \
1030 context_unsafe( \
1031 rcu_check_sparse(p, __rcu); \
1032 WRITE_ONCE(p, RCU_INITIALIZER(v)); \
1033 )
1034
1035/**
1036 * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
1037 * @p: The pointer to be initialized.
1038 * @v: The value to initialized the pointer to.
1039 *
1040 * GCC-style initialization for an RCU-protected pointer in a structure field.
1041 */
1042#define RCU_POINTER_INITIALIZER(p, v) \
1043 .p = RCU_INITIALIZER(v)
1044
1045/**
1046 * kfree_rcu() - kfree an object after a grace period.
1047 * @ptr: pointer to kfree for double-argument invocations.
1048 * @rhf: the name of the struct rcu_head within the type of @ptr.
1049 *
1050 * Many rcu callbacks functions just call kfree() on the base structure.
1051 * These functions are trivial, but their size adds up, and furthermore
1052 * when they are used in a kernel module, that module must invoke the
1053 * high-latency rcu_barrier() function at module-unload time.
1054 *
1055 * The kfree_rcu() function handles this issue. In order to have a universal
1056 * callback function handling different offsets of rcu_head, the callback needs
1057 * to determine the starting address of the freed object, which can be a large
1058 * kmalloc or vmalloc allocation. To allow simply aligning the pointer down to
1059 * page boundary for those, only offsets up to 4095 bytes can be accommodated.
1060 * If the offset is larger than 4095 bytes, a compile-time error will
1061 * be generated in kvfree_rcu_arg_2(). If this error is triggered, you can
1062 * either fall back to use of call_rcu() or rearrange the structure to
1063 * position the rcu_head structure into the first 4096 bytes.
1064 *
1065 * The object to be freed can be allocated either by kmalloc(),
1066 * kmalloc_nolock(), or kmem_cache_alloc().
1067 *
1068 * Note that the allowable offset might decrease in the future.
1069 *
1070 * The BUILD_BUG_ON check must not involve any function calls, hence the
1071 * checks are done in macros here.
1072 */
1073#define kfree_rcu(ptr, rhf) kvfree_rcu_arg_2(ptr, rhf)
1074#define kvfree_rcu(ptr, rhf) kvfree_rcu_arg_2(ptr, rhf)
1075
1076/**
1077 * kfree_rcu_mightsleep() - kfree an object after a grace period.
1078 * @ptr: pointer to kfree for single-argument invocations.
1079 *
1080 * When it comes to head-less variant, only one argument
1081 * is passed and that is just a pointer which has to be
1082 * freed after a grace period. Therefore the semantic is
1083 *
1084 * kfree_rcu_mightsleep(ptr);
1085 *
1086 * where @ptr is the pointer to be freed by kvfree().
1087 *
1088 * Please note, head-less way of freeing is permitted to
1089 * use from a context that has to follow might_sleep()
1090 * annotation. Otherwise, please switch and embed the
1091 * rcu_head structure within the type of @ptr.
1092 */
1093#define kfree_rcu_mightsleep(ptr) kvfree_rcu_arg_1(ptr)
1094#define kvfree_rcu_mightsleep(ptr) kvfree_rcu_arg_1(ptr)
1095
1096/*
1097 * In mm/slab_common.c, no suitable header to include here.
1098 */
1099void kvfree_call_rcu(struct rcu_head *head, void *ptr);
1100
1101/*
1102 * The BUILD_BUG_ON() makes sure the rcu_head offset can be handled. See the
1103 * comment of kfree_rcu() for details.
1104 */
1105#define kvfree_rcu_arg_2(ptr, rhf) \
1106do { \
1107 typeof (ptr) ___p = (ptr); \
1108 \
1109 if (___p) { \
1110 BUILD_BUG_ON(offsetof(typeof(*(ptr)), rhf) >= 4096); \
1111 kvfree_call_rcu(&((___p)->rhf), (void *) (___p)); \
1112 } \
1113} while (0)
1114
1115#define kvfree_rcu_arg_1(ptr) \
1116do { \
1117 typeof(ptr) ___p = (ptr); \
1118 \
1119 if (___p) \
1120 kvfree_call_rcu(NULL, (void *) (___p)); \
1121} while (0)
1122
1123/*
1124 * Place this after a lock-acquisition primitive to guarantee that
1125 * an UNLOCK+LOCK pair acts as a full barrier. This guarantee applies
1126 * if the UNLOCK and LOCK are executed by the same CPU or if the
1127 * UNLOCK and LOCK operate on the same lock variable.
1128 */
1129#ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE
1130#define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */
1131#else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
1132#define smp_mb__after_unlock_lock() do { } while (0)
1133#endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
1134
1135
1136/* Has the specified rcu_head structure been handed to call_rcu()? */
1137
1138/**
1139 * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu()
1140 * @rhp: The rcu_head structure to initialize.
1141 *
1142 * If you intend to invoke rcu_head_after_call_rcu() to test whether a
1143 * given rcu_head structure has already been passed to call_rcu(), then
1144 * you must also invoke this rcu_head_init() function on it just after
1145 * allocating that structure. Calls to this function must not race with
1146 * calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation.
1147 */
1148static inline void rcu_head_init(struct rcu_head *rhp)
1149{
1150 rhp->func = (rcu_callback_t)~0L;
1151}
1152
1153/**
1154 * rcu_head_after_call_rcu() - Has this rcu_head been passed to call_rcu()?
1155 * @rhp: The rcu_head structure to test.
1156 * @f: The function passed to call_rcu() along with @rhp.
1157 *
1158 * Returns @true if the @rhp has been passed to call_rcu() with @func,
1159 * and @false otherwise. Emits a warning in any other case, including
1160 * the case where @rhp has already been invoked after a grace period.
1161 * Calls to this function must not race with callback invocation. One way
1162 * to avoid such races is to enclose the call to rcu_head_after_call_rcu()
1163 * in an RCU read-side critical section that includes a read-side fetch
1164 * of the pointer to the structure containing @rhp.
1165 */
1166static inline bool
1167rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f)
1168{
1169 rcu_callback_t func = READ_ONCE(rhp->func);
1170
1171 if (func == f)
1172 return true;
1173 WARN_ON_ONCE(func != (rcu_callback_t)~0L);
1174 return false;
1175}
1176
1177/* kernel/ksysfs.c definitions */
1178extern int rcu_expedited;
1179extern int rcu_normal;
1180
1181DEFINE_LOCK_GUARD_0(rcu, rcu_read_lock(), rcu_read_unlock())
1182DECLARE_LOCK_GUARD_0_ATTRS(rcu, __acquires_shared(RCU), __releases_shared(RCU))
1183
1184#endif /* __LINUX_RCUPDATE_H */