Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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 * rcu_trace_implies_rcu_gp - does an RCU Tasks Trace grace period imply an RCU grace period?
210 *
211 * As an accident of implementation, an RCU Tasks Trace grace period also
212 * acts as an RCU grace period. However, this could change at any time.
213 * Code relying on this accident must call this function to verify that
214 * this accident is still happening.
215 *
216 * You have been warned!
217 */
218static inline bool rcu_trace_implies_rcu_gp(void) { return true; }
219
220/**
221 * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU
222 *
223 * This macro resembles cond_resched(), except that it is defined to
224 * report potential quiescent states to RCU-tasks even if the cond_resched()
225 * machinery were to be shut off, as some advocate for PREEMPTION kernels.
226 */
227#define cond_resched_tasks_rcu_qs() \
228do { \
229 rcu_tasks_qs(current, false); \
230 cond_resched(); \
231} while (0)
232
233/**
234 * rcu_softirq_qs_periodic - Report RCU and RCU-Tasks quiescent states
235 * @old_ts: jiffies at start of processing.
236 *
237 * This helper is for long-running softirq handlers, such as NAPI threads in
238 * networking. The caller should initialize the variable passed in as @old_ts
239 * at the beginning of the softirq handler. When invoked frequently, this macro
240 * will invoke rcu_softirq_qs() every 100 milliseconds thereafter, which will
241 * provide both RCU and RCU-Tasks quiescent states. Note that this macro
242 * modifies its old_ts argument.
243 *
244 * Because regions of code that have disabled softirq act as RCU read-side
245 * critical sections, this macro should be invoked with softirq (and
246 * preemption) enabled.
247 *
248 * The macro is not needed when CONFIG_PREEMPT_RT is defined. RT kernels would
249 * have more chance to invoke schedule() calls and provide necessary quiescent
250 * states. As a contrast, calling cond_resched() only won't achieve the same
251 * effect because cond_resched() does not provide RCU-Tasks quiescent states.
252 */
253#define rcu_softirq_qs_periodic(old_ts) \
254do { \
255 if (!IS_ENABLED(CONFIG_PREEMPT_RT) && \
256 time_after(jiffies, (old_ts) + HZ / 10)) { \
257 preempt_disable(); \
258 rcu_softirq_qs(); \
259 preempt_enable(); \
260 (old_ts) = jiffies; \
261 } \
262} while (0)
263
264/*
265 * Infrastructure to implement the synchronize_() primitives in
266 * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
267 */
268
269#if defined(CONFIG_TREE_RCU)
270#include <linux/rcutree.h>
271#elif defined(CONFIG_TINY_RCU)
272#include <linux/rcutiny.h>
273#else
274#error "Unknown RCU implementation specified to kernel configuration"
275#endif
276
277/*
278 * The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls
279 * are needed for dynamic initialization and destruction of rcu_head
280 * on the stack, and init_rcu_head()/destroy_rcu_head() are needed for
281 * dynamic initialization and destruction of statically allocated rcu_head
282 * structures. However, rcu_head structures allocated dynamically in the
283 * heap don't need any initialization.
284 */
285#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
286void init_rcu_head(struct rcu_head *head);
287void destroy_rcu_head(struct rcu_head *head);
288void init_rcu_head_on_stack(struct rcu_head *head);
289void destroy_rcu_head_on_stack(struct rcu_head *head);
290#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
291static inline void init_rcu_head(struct rcu_head *head) { }
292static inline void destroy_rcu_head(struct rcu_head *head) { }
293static inline void init_rcu_head_on_stack(struct rcu_head *head) { }
294static inline void destroy_rcu_head_on_stack(struct rcu_head *head) { }
295#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
296
297#if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
298bool rcu_lockdep_current_cpu_online(void);
299#else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
300static inline bool rcu_lockdep_current_cpu_online(void) { return true; }
301#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
302
303extern struct lockdep_map rcu_lock_map;
304extern struct lockdep_map rcu_bh_lock_map;
305extern struct lockdep_map rcu_sched_lock_map;
306extern struct lockdep_map rcu_callback_map;
307
308#ifdef CONFIG_DEBUG_LOCK_ALLOC
309
310static inline void rcu_lock_acquire(struct lockdep_map *map)
311{
312 lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
313}
314
315static inline void rcu_try_lock_acquire(struct lockdep_map *map)
316{
317 lock_acquire(map, 0, 1, 2, 0, NULL, _THIS_IP_);
318}
319
320static inline void rcu_lock_release(struct lockdep_map *map)
321{
322 lock_release(map, _THIS_IP_);
323}
324
325int debug_lockdep_rcu_enabled(void);
326int rcu_read_lock_held(void);
327int rcu_read_lock_bh_held(void);
328int rcu_read_lock_sched_held(void);
329int rcu_read_lock_any_held(void);
330
331#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
332
333# define rcu_lock_acquire(a) do { } while (0)
334# define rcu_try_lock_acquire(a) do { } while (0)
335# define rcu_lock_release(a) do { } while (0)
336
337static inline int rcu_read_lock_held(void)
338{
339 return 1;
340}
341
342static inline int rcu_read_lock_bh_held(void)
343{
344 return 1;
345}
346
347static inline int rcu_read_lock_sched_held(void)
348{
349 return !preemptible();
350}
351
352static inline int rcu_read_lock_any_held(void)
353{
354 return !preemptible();
355}
356
357static inline int debug_lockdep_rcu_enabled(void)
358{
359 return 0;
360}
361
362#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
363
364#ifdef CONFIG_PROVE_RCU
365
366/**
367 * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met
368 * @c: condition to check
369 * @s: informative message
370 *
371 * This checks debug_lockdep_rcu_enabled() before checking (c) to
372 * prevent early boot splats due to lockdep not yet being initialized,
373 * and rechecks it after checking (c) to prevent false-positive splats
374 * due to races with lockdep being disabled. See commit 3066820034b5dd
375 * ("rcu: Reject RCU_LOCKDEP_WARN() false positives") for more detail.
376 */
377#define RCU_LOCKDEP_WARN(c, s) \
378 do { \
379 static bool __section(".data..unlikely") __warned; \
380 if (debug_lockdep_rcu_enabled() && (c) && \
381 debug_lockdep_rcu_enabled() && !__warned) { \
382 __warned = true; \
383 lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
384 } \
385 } while (0)
386
387#ifndef CONFIG_PREEMPT_RCU
388static inline void rcu_preempt_sleep_check(void)
389{
390 RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
391 "Illegal context switch in RCU read-side critical section");
392}
393#else // #ifndef CONFIG_PREEMPT_RCU
394static inline void rcu_preempt_sleep_check(void) { }
395#endif // #else // #ifndef CONFIG_PREEMPT_RCU
396
397#define rcu_sleep_check() \
398 do { \
399 rcu_preempt_sleep_check(); \
400 if (!IS_ENABLED(CONFIG_PREEMPT_RT)) \
401 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map), \
402 "Illegal context switch in RCU-bh read-side critical section"); \
403 RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), \
404 "Illegal context switch in RCU-sched read-side critical section"); \
405 } while (0)
406
407// See RCU_LOCKDEP_WARN() for an explanation of the double call to
408// debug_lockdep_rcu_enabled().
409static __always_inline bool lockdep_assert_rcu_helper(bool c, const struct __ctx_lock_RCU *ctx)
410 __assumes_shared_ctx_lock(RCU) __assumes_shared_ctx_lock(ctx)
411{
412 return debug_lockdep_rcu_enabled() &&
413 (c || !rcu_is_watching() || !rcu_lockdep_current_cpu_online()) &&
414 debug_lockdep_rcu_enabled();
415}
416
417/**
418 * lockdep_assert_in_rcu_read_lock - WARN if not protected by rcu_read_lock()
419 *
420 * Splats if lockdep is enabled and there is no rcu_read_lock() in effect.
421 */
422#define lockdep_assert_in_rcu_read_lock() \
423 WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_lock_map), RCU))
424
425/**
426 * lockdep_assert_in_rcu_read_lock_bh - WARN if not protected by rcu_read_lock_bh()
427 *
428 * Splats if lockdep is enabled and there is no rcu_read_lock_bh() in effect.
429 * Note that local_bh_disable() and friends do not suffice here, instead an
430 * actual rcu_read_lock_bh() is required.
431 */
432#define lockdep_assert_in_rcu_read_lock_bh() \
433 WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_bh_lock_map), RCU_BH))
434
435/**
436 * lockdep_assert_in_rcu_read_lock_sched - WARN if not protected by rcu_read_lock_sched()
437 *
438 * Splats if lockdep is enabled and there is no rcu_read_lock_sched()
439 * in effect. Note that preempt_disable() and friends do not suffice here,
440 * instead an actual rcu_read_lock_sched() is required.
441 */
442#define lockdep_assert_in_rcu_read_lock_sched() \
443 WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_sched_lock_map), RCU_SCHED))
444
445/**
446 * lockdep_assert_in_rcu_reader - WARN if not within some type of RCU reader
447 *
448 * Splats if lockdep is enabled and there is no RCU reader of any
449 * type in effect. Note that regions of code protected by things like
450 * preempt_disable, local_bh_disable(), and local_irq_disable() all qualify
451 * as RCU readers.
452 *
453 * Note that this will never trigger in PREEMPT_NONE or PREEMPT_VOLUNTARY
454 * kernels that are not also built with PREEMPT_COUNT. But if you have
455 * lockdep enabled, you might as well also enable PREEMPT_COUNT.
456 */
457#define lockdep_assert_in_rcu_reader() \
458 WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_lock_map) && \
459 !lock_is_held(&rcu_bh_lock_map) && \
460 !lock_is_held(&rcu_sched_lock_map) && \
461 preemptible(), RCU))
462
463#else /* #ifdef CONFIG_PROVE_RCU */
464
465#define RCU_LOCKDEP_WARN(c, s) do { } while (0 && (c))
466#define rcu_sleep_check() do { } while (0)
467
468#define lockdep_assert_in_rcu_read_lock() __assume_shared_ctx_lock(RCU)
469#define lockdep_assert_in_rcu_read_lock_bh() __assume_shared_ctx_lock(RCU_BH)
470#define lockdep_assert_in_rcu_read_lock_sched() __assume_shared_ctx_lock(RCU_SCHED)
471#define lockdep_assert_in_rcu_reader() __assume_shared_ctx_lock(RCU)
472
473#endif /* #else #ifdef CONFIG_PROVE_RCU */
474
475/*
476 * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
477 * and rcu_assign_pointer(). Some of these could be folded into their
478 * callers, but they are left separate in order to ease introduction of
479 * multiple pointers markings to match different RCU implementations
480 * (e.g., __srcu), should this make sense in the future.
481 */
482
483#ifdef __CHECKER__
484#define rcu_check_sparse(p, space) \
485 ((void)(((typeof(*p) space *)p) == p))
486#else /* #ifdef __CHECKER__ */
487#define rcu_check_sparse(p, space)
488#endif /* #else #ifdef __CHECKER__ */
489
490#define __unrcu_pointer(p, local) \
491context_unsafe( \
492 typeof(*p) *local = (typeof(*p) *__force)(p); \
493 rcu_check_sparse(p, __rcu); \
494 ((typeof(*p) __force __kernel *)(local)) \
495)
496/**
497 * unrcu_pointer - mark a pointer as not being RCU protected
498 * @p: pointer needing to lose its __rcu property
499 *
500 * Converts @p from an __rcu pointer to a __kernel pointer.
501 * This allows an __rcu pointer to be used with xchg() and friends.
502 */
503#define unrcu_pointer(p) __unrcu_pointer(p, __UNIQUE_ID(rcu))
504
505#define __rcu_access_pointer(p, local, space) \
506({ \
507 typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \
508 rcu_check_sparse(p, space); \
509 ((typeof(*p) __force __kernel *)(local)); \
510})
511#define __rcu_dereference_check(p, local, c, space) \
512({ \
513 /* Dependency order vs. p above. */ \
514 typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \
515 RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
516 rcu_check_sparse(p, space); \
517 ((typeof(*p) __force __kernel *)(local)); \
518})
519#define __rcu_dereference_protected(p, local, c, space) \
520({ \
521 RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
522 rcu_check_sparse(p, space); \
523 ((typeof(*p) __force __kernel *)(p)); \
524})
525#define __rcu_dereference_raw(p, local) \
526({ \
527 /* Dependency order vs. p above. */ \
528 typeof(p) local = READ_ONCE(p); \
529 ((typeof(*p) __force __kernel *)(local)); \
530})
531#define rcu_dereference_raw(p) __rcu_dereference_raw(p, __UNIQUE_ID(rcu))
532
533/**
534 * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
535 * @v: The value to statically initialize with.
536 */
537#define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
538
539/**
540 * rcu_assign_pointer() - assign to RCU-protected pointer
541 * @p: pointer to assign to
542 * @v: value to assign (publish)
543 *
544 * Assigns the specified value to the specified RCU-protected
545 * pointer, ensuring that any concurrent RCU readers will see
546 * any prior initialization.
547 *
548 * Inserts memory barriers on architectures that require them
549 * (which is most of them), and also prevents the compiler from
550 * reordering the code that initializes the structure after the pointer
551 * assignment. More importantly, this call documents which pointers
552 * will be dereferenced by RCU read-side code.
553 *
554 * In some special cases, you may use RCU_INIT_POINTER() instead
555 * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due
556 * to the fact that it does not constrain either the CPU or the compiler.
557 * That said, using RCU_INIT_POINTER() when you should have used
558 * rcu_assign_pointer() is a very bad thing that results in
559 * impossible-to-diagnose memory corruption. So please be careful.
560 * See the RCU_INIT_POINTER() comment header for details.
561 *
562 * Note that rcu_assign_pointer() evaluates each of its arguments only
563 * once, appearances notwithstanding. One of the "extra" evaluations
564 * is in typeof() and the other visible only to sparse (__CHECKER__),
565 * neither of which actually execute the argument. As with most cpp
566 * macros, this execute-arguments-only-once property is important, so
567 * please be careful when making changes to rcu_assign_pointer() and the
568 * other macros that it invokes.
569 */
570#define rcu_assign_pointer(p, v) \
571context_unsafe( \
572 uintptr_t _r_a_p__v = (uintptr_t)(v); \
573 rcu_check_sparse(p, __rcu); \
574 \
575 if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \
576 WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \
577 else \
578 smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \
579)
580
581/**
582 * rcu_replace_pointer() - replace an RCU pointer, returning its old value
583 * @rcu_ptr: RCU pointer, whose old value is returned
584 * @ptr: regular pointer
585 * @c: the lockdep conditions under which the dereference will take place
586 *
587 * Perform a replacement, where @rcu_ptr is an RCU-annotated
588 * pointer and @c is the lockdep argument that is passed to the
589 * rcu_dereference_protected() call used to read that pointer. The old
590 * value of @rcu_ptr is returned, and @rcu_ptr is set to @ptr.
591 */
592#define rcu_replace_pointer(rcu_ptr, ptr, c) \
593({ \
594 typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c)); \
595 rcu_assign_pointer((rcu_ptr), (ptr)); \
596 __tmp; \
597})
598
599/**
600 * rcu_access_pointer() - fetch RCU pointer with no dereferencing
601 * @p: The pointer to read
602 *
603 * Return the value of the specified RCU-protected pointer, but omit the
604 * lockdep checks for being in an RCU read-side critical section. This is
605 * useful when the value of this pointer is accessed, but the pointer is
606 * not dereferenced, for example, when testing an RCU-protected pointer
607 * against NULL. Although rcu_access_pointer() may also be used in cases
608 * where update-side locks prevent the value of the pointer from changing,
609 * you should instead use rcu_dereference_protected() for this use case.
610 * Within an RCU read-side critical section, there is little reason to
611 * use rcu_access_pointer().
612 *
613 * It is usually best to test the rcu_access_pointer() return value
614 * directly in order to avoid accidental dereferences being introduced
615 * by later inattentive changes. In other words, assigning the
616 * rcu_access_pointer() return value to a local variable results in an
617 * accident waiting to happen.
618 *
619 * It is also permissible to use rcu_access_pointer() when read-side
620 * access to the pointer was removed at least one grace period ago, as is
621 * the case in the context of the RCU callback that is freeing up the data,
622 * or after a synchronize_rcu() returns. This can be useful when tearing
623 * down multi-linked structures after a grace period has elapsed. However,
624 * rcu_dereference_protected() is normally preferred for this use case.
625 */
626#define rcu_access_pointer(p) __rcu_access_pointer((p), __UNIQUE_ID(rcu), __rcu)
627
628/**
629 * rcu_dereference_check() - rcu_dereference with debug checking
630 * @p: The pointer to read, prior to dereferencing
631 * @c: The conditions under which the dereference will take place
632 *
633 * Do an rcu_dereference(), but check that the conditions under which the
634 * dereference will take place are correct. Typically the conditions
635 * indicate the various locking conditions that should be held at that
636 * point. The check should return true if the conditions are satisfied.
637 * An implicit check for being in an RCU read-side critical section
638 * (rcu_read_lock()) is included.
639 *
640 * For example:
641 *
642 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
643 *
644 * could be used to indicate to lockdep that foo->bar may only be dereferenced
645 * if either rcu_read_lock() is held, or that the lock required to replace
646 * the bar struct at foo->bar is held.
647 *
648 * Note that the list of conditions may also include indications of when a lock
649 * need not be held, for example during initialisation or destruction of the
650 * target struct:
651 *
652 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
653 * atomic_read(&foo->usage) == 0);
654 *
655 * Inserts memory barriers on architectures that require them
656 * (currently only the Alpha), prevents the compiler from refetching
657 * (and from merging fetches), and, more importantly, documents exactly
658 * which pointers are protected by RCU and checks that the pointer is
659 * annotated as __rcu.
660 */
661#define rcu_dereference_check(p, c) \
662 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
663 (c) || rcu_read_lock_held(), __rcu)
664
665/**
666 * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
667 * @p: The pointer to read, prior to dereferencing
668 * @c: The conditions under which the dereference will take place
669 *
670 * This is the RCU-bh counterpart to rcu_dereference_check(). However,
671 * please note that starting in v5.0 kernels, vanilla RCU grace periods
672 * wait for local_bh_disable() regions of code in addition to regions of
673 * code demarked by rcu_read_lock() and rcu_read_unlock(). This means
674 * that synchronize_rcu(), call_rcu, and friends all take not only
675 * rcu_read_lock() but also rcu_read_lock_bh() into account.
676 */
677#define rcu_dereference_bh_check(p, c) \
678 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
679 (c) || rcu_read_lock_bh_held(), __rcu)
680
681/**
682 * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
683 * @p: The pointer to read, prior to dereferencing
684 * @c: The conditions under which the dereference will take place
685 *
686 * This is the RCU-sched counterpart to rcu_dereference_check().
687 * However, please note that starting in v5.0 kernels, vanilla RCU grace
688 * periods wait for preempt_disable() regions of code in addition to
689 * regions of code demarked by rcu_read_lock() and rcu_read_unlock().
690 * This means that synchronize_rcu(), call_rcu, and friends all take not
691 * only rcu_read_lock() but also rcu_read_lock_sched() into account.
692 */
693#define rcu_dereference_sched_check(p, c) \
694 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
695 (c) || rcu_read_lock_sched_held(), \
696 __rcu)
697
698/**
699 * rcu_dereference_all_check() - rcu_dereference_all with debug checking
700 * @p: The pointer to read, prior to dereferencing
701 * @c: The conditions under which the dereference will take place
702 *
703 * This is similar to rcu_dereference_check(), but allows protection
704 * by all forms of vanilla RCU readers, including preemption disabled,
705 * bh-disabled, and interrupt-disabled regions of code. Note that "vanilla
706 * RCU" excludes SRCU and the various Tasks RCU flavors. Please note
707 * that this macro should not be backported to any Linux-kernel version
708 * preceding v5.0 due to changes in synchronize_rcu() semantics prior
709 * to that version.
710 */
711#define rcu_dereference_all_check(p, c) \
712 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
713 (c) || rcu_read_lock_any_held(), \
714 __rcu)
715
716/*
717 * The tracing infrastructure traces RCU (we want that), but unfortunately
718 * some of the RCU checks causes tracing to lock up the system.
719 *
720 * The no-tracing version of rcu_dereference_raw() must not call
721 * rcu_read_lock_held().
722 */
723#define rcu_dereference_raw_check(p) \
724 __rcu_dereference_check((p), __UNIQUE_ID(rcu), 1, __rcu)
725
726/**
727 * rcu_dereference_protected() - fetch RCU pointer when updates prevented
728 * @p: The pointer to read, prior to dereferencing
729 * @c: The conditions under which the dereference will take place
730 *
731 * Return the value of the specified RCU-protected pointer, but omit
732 * the READ_ONCE(). This is useful in cases where update-side locks
733 * prevent the value of the pointer from changing. Please note that this
734 * primitive does *not* prevent the compiler from repeating this reference
735 * or combining it with other references, so it should not be used without
736 * protection of appropriate locks.
737 *
738 * This function is only for update-side use. Using this function
739 * when protected only by rcu_read_lock() will result in infrequent
740 * but very ugly failures.
741 */
742#define rcu_dereference_protected(p, c) \
743 __rcu_dereference_protected((p), __UNIQUE_ID(rcu), (c), __rcu)
744
745
746/**
747 * rcu_dereference() - fetch RCU-protected pointer for dereferencing
748 * @p: The pointer to read, prior to dereferencing
749 *
750 * This is a simple wrapper around rcu_dereference_check().
751 */
752#define rcu_dereference(p) rcu_dereference_check(p, 0)
753
754/**
755 * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
756 * @p: The pointer to read, prior to dereferencing
757 *
758 * Makes rcu_dereference_check() do the dirty work.
759 */
760#define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
761
762/**
763 * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
764 * @p: The pointer to read, prior to dereferencing
765 *
766 * Makes rcu_dereference_check() do the dirty work.
767 */
768#define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
769
770/**
771 * rcu_dereference_all() - fetch RCU-all-protected pointer for dereferencing
772 * @p: The pointer to read, prior to dereferencing
773 *
774 * Makes rcu_dereference_check() do the dirty work.
775 */
776#define rcu_dereference_all(p) rcu_dereference_all_check(p, 0)
777
778/**
779 * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism
780 * @p: The pointer to hand off
781 *
782 * This is simply an identity function, but it documents where a pointer
783 * is handed off from RCU to some other synchronization mechanism, for
784 * example, reference counting or locking. In C11, it would map to
785 * kill_dependency(). It could be used as follows::
786 *
787 * rcu_read_lock();
788 * p = rcu_dereference(gp);
789 * long_lived = is_long_lived(p);
790 * if (long_lived) {
791 * if (!atomic_inc_not_zero(p->refcnt))
792 * long_lived = false;
793 * else
794 * p = rcu_pointer_handoff(p);
795 * }
796 * rcu_read_unlock();
797 */
798#define rcu_pointer_handoff(p) (p)
799
800/**
801 * rcu_read_lock() - mark the beginning of an RCU read-side critical section
802 *
803 * When synchronize_rcu() is invoked on one CPU while other CPUs
804 * are within RCU read-side critical sections, then the
805 * synchronize_rcu() is guaranteed to block until after all the other
806 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
807 * on one CPU while other CPUs are within RCU read-side critical
808 * sections, invocation of the corresponding RCU callback is deferred
809 * until after the all the other CPUs exit their critical sections.
810 *
811 * Both synchronize_rcu() and call_rcu() also wait for regions of code
812 * with preemption disabled, including regions of code with interrupts or
813 * softirqs disabled.
814 *
815 * Note, however, that RCU callbacks are permitted to run concurrently
816 * with new RCU read-side critical sections. One way that this can happen
817 * is via the following sequence of events: (1) CPU 0 enters an RCU
818 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
819 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
820 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
821 * callback is invoked. This is legal, because the RCU read-side critical
822 * section that was running concurrently with the call_rcu() (and which
823 * therefore might be referencing something that the corresponding RCU
824 * callback would free up) has completed before the corresponding
825 * RCU callback is invoked.
826 *
827 * RCU read-side critical sections may be nested. Any deferred actions
828 * will be deferred until the outermost RCU read-side critical section
829 * completes.
830 *
831 * You can avoid reading and understanding the next paragraph by
832 * following this rule: don't put anything in an rcu_read_lock() RCU
833 * read-side critical section that would block in a !PREEMPTION kernel.
834 * But if you want the full story, read on!
835 *
836 * In non-preemptible RCU implementations (pure TREE_RCU and TINY_RCU),
837 * it is illegal to block while in an RCU read-side critical section.
838 * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPTION
839 * kernel builds, RCU read-side critical sections may be preempted,
840 * but explicit blocking is illegal. Finally, in preemptible RCU
841 * implementations in real-time (with -rt patchset) kernel builds, RCU
842 * read-side critical sections may be preempted and they may also block, but
843 * only when acquiring spinlocks that are subject to priority inheritance.
844 */
845static __always_inline void rcu_read_lock(void)
846 __acquires_shared(RCU)
847{
848 __rcu_read_lock();
849 __acquire_shared(RCU);
850 rcu_lock_acquire(&rcu_lock_map);
851 RCU_LOCKDEP_WARN(!rcu_is_watching(),
852 "rcu_read_lock() used illegally while idle");
853}
854
855/*
856 * So where is rcu_write_lock()? It does not exist, as there is no
857 * way for writers to lock out RCU readers. This is a feature, not
858 * a bug -- this property is what provides RCU's performance benefits.
859 * Of course, writers must coordinate with each other. The normal
860 * spinlock primitives work well for this, but any other technique may be
861 * used as well. RCU does not care how the writers keep out of each
862 * others' way, as long as they do so.
863 */
864
865/**
866 * rcu_read_unlock() - marks the end of an RCU read-side critical section.
867 *
868 * In almost all situations, rcu_read_unlock() is immune from deadlock.
869 * This deadlock immunity also extends to the scheduler's runqueue
870 * and priority-inheritance spinlocks, courtesy of the quiescent-state
871 * deferral that is carried out when rcu_read_unlock() is invoked with
872 * interrupts disabled.
873 *
874 * See rcu_read_lock() for more information.
875 */
876static inline void rcu_read_unlock(void)
877 __releases_shared(RCU)
878{
879 RCU_LOCKDEP_WARN(!rcu_is_watching(),
880 "rcu_read_unlock() used illegally while idle");
881 rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
882 __release_shared(RCU);
883 __rcu_read_unlock();
884}
885
886/**
887 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
888 *
889 * This is equivalent to rcu_read_lock(), but also disables softirqs.
890 * Note that anything else that disables softirqs can also serve as an RCU
891 * read-side critical section. However, please note that this equivalence
892 * applies only to v5.0 and later. Before v5.0, rcu_read_lock() and
893 * rcu_read_lock_bh() were unrelated.
894 *
895 * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
896 * must occur in the same context, for example, it is illegal to invoke
897 * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
898 * was invoked from some other task.
899 */
900static inline void rcu_read_lock_bh(void)
901 __acquires_shared(RCU) __acquires_shared(RCU_BH)
902{
903 local_bh_disable();
904 __acquire_shared(RCU);
905 __acquire_shared(RCU_BH);
906 rcu_lock_acquire(&rcu_bh_lock_map);
907 RCU_LOCKDEP_WARN(!rcu_is_watching(),
908 "rcu_read_lock_bh() used illegally while idle");
909}
910
911/**
912 * rcu_read_unlock_bh() - marks the end of a softirq-only RCU critical section
913 *
914 * See rcu_read_lock_bh() for more information.
915 */
916static inline void rcu_read_unlock_bh(void)
917 __releases_shared(RCU) __releases_shared(RCU_BH)
918{
919 RCU_LOCKDEP_WARN(!rcu_is_watching(),
920 "rcu_read_unlock_bh() used illegally while idle");
921 rcu_lock_release(&rcu_bh_lock_map);
922 __release_shared(RCU_BH);
923 __release_shared(RCU);
924 local_bh_enable();
925}
926
927/**
928 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
929 *
930 * This is equivalent to rcu_read_lock(), but also disables preemption.
931 * Read-side critical sections can also be introduced by anything else that
932 * disables preemption, including local_irq_disable() and friends. However,
933 * please note that the equivalence to rcu_read_lock() applies only to
934 * v5.0 and later. Before v5.0, rcu_read_lock() and rcu_read_lock_sched()
935 * were unrelated.
936 *
937 * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
938 * must occur in the same context, for example, it is illegal to invoke
939 * rcu_read_unlock_sched() from process context if the matching
940 * rcu_read_lock_sched() was invoked from an NMI handler.
941 */
942static inline void rcu_read_lock_sched(void)
943 __acquires_shared(RCU) __acquires_shared(RCU_SCHED)
944{
945 preempt_disable();
946 __acquire_shared(RCU);
947 __acquire_shared(RCU_SCHED);
948 rcu_lock_acquire(&rcu_sched_lock_map);
949 RCU_LOCKDEP_WARN(!rcu_is_watching(),
950 "rcu_read_lock_sched() used illegally while idle");
951}
952
953/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
954static inline notrace void rcu_read_lock_sched_notrace(void)
955 __acquires_shared(RCU) __acquires_shared(RCU_SCHED)
956{
957 preempt_disable_notrace();
958 __acquire_shared(RCU);
959 __acquire_shared(RCU_SCHED);
960}
961
962/**
963 * rcu_read_unlock_sched() - marks the end of a RCU-classic critical section
964 *
965 * See rcu_read_lock_sched() for more information.
966 */
967static inline void rcu_read_unlock_sched(void)
968 __releases_shared(RCU) __releases_shared(RCU_SCHED)
969{
970 RCU_LOCKDEP_WARN(!rcu_is_watching(),
971 "rcu_read_unlock_sched() used illegally while idle");
972 rcu_lock_release(&rcu_sched_lock_map);
973 __release_shared(RCU_SCHED);
974 __release_shared(RCU);
975 preempt_enable();
976}
977
978/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
979static inline notrace void rcu_read_unlock_sched_notrace(void)
980 __releases_shared(RCU) __releases_shared(RCU_SCHED)
981{
982 __release_shared(RCU_SCHED);
983 __release_shared(RCU);
984 preempt_enable_notrace();
985}
986
987static __always_inline void rcu_read_lock_dont_migrate(void)
988 __acquires_shared(RCU)
989{
990 if (IS_ENABLED(CONFIG_PREEMPT_RCU))
991 migrate_disable();
992 rcu_read_lock();
993}
994
995static inline void rcu_read_unlock_migrate(void)
996 __releases_shared(RCU)
997{
998 rcu_read_unlock();
999 if (IS_ENABLED(CONFIG_PREEMPT_RCU))
1000 migrate_enable();
1001}
1002
1003/**
1004 * RCU_INIT_POINTER() - initialize an RCU protected pointer
1005 * @p: The pointer to be initialized.
1006 * @v: The value to initialized the pointer to.
1007 *
1008 * Initialize an RCU-protected pointer in special cases where readers
1009 * do not need ordering constraints on the CPU or the compiler. These
1010 * special cases are:
1011 *
1012 * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer *or*
1013 * 2. The caller has taken whatever steps are required to prevent
1014 * RCU readers from concurrently accessing this pointer *or*
1015 * 3. The referenced data structure has already been exposed to
1016 * readers either at compile time or via rcu_assign_pointer() *and*
1017 *
1018 * a. You have not made *any* reader-visible changes to
1019 * this structure since then *or*
1020 * b. It is OK for readers accessing this structure from its
1021 * new location to see the old state of the structure. (For
1022 * example, the changes were to statistical counters or to
1023 * other state where exact synchronization is not required.)
1024 *
1025 * Failure to follow these rules governing use of RCU_INIT_POINTER() will
1026 * result in impossible-to-diagnose memory corruption. As in the structures
1027 * will look OK in crash dumps, but any concurrent RCU readers might
1028 * see pre-initialized values of the referenced data structure. So
1029 * please be very careful how you use RCU_INIT_POINTER()!!!
1030 *
1031 * If you are creating an RCU-protected linked structure that is accessed
1032 * by a single external-to-structure RCU-protected pointer, then you may
1033 * use RCU_INIT_POINTER() to initialize the internal RCU-protected
1034 * pointers, but you must use rcu_assign_pointer() to initialize the
1035 * external-to-structure pointer *after* you have completely initialized
1036 * the reader-accessible portions of the linked structure.
1037 *
1038 * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
1039 * ordering guarantees for either the CPU or the compiler.
1040 */
1041#define RCU_INIT_POINTER(p, v) \
1042 context_unsafe( \
1043 rcu_check_sparse(p, __rcu); \
1044 WRITE_ONCE(p, RCU_INITIALIZER(v)); \
1045 )
1046
1047/**
1048 * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
1049 * @p: The pointer to be initialized.
1050 * @v: The value to initialized the pointer to.
1051 *
1052 * GCC-style initialization for an RCU-protected pointer in a structure field.
1053 */
1054#define RCU_POINTER_INITIALIZER(p, v) \
1055 .p = RCU_INITIALIZER(v)
1056
1057/**
1058 * kfree_rcu() - kfree an object after a grace period.
1059 * @ptr: pointer to kfree for double-argument invocations.
1060 * @rhf: the name of the struct rcu_head within the type of @ptr.
1061 *
1062 * Many rcu callbacks functions just call kfree() on the base structure.
1063 * These functions are trivial, but their size adds up, and furthermore
1064 * when they are used in a kernel module, that module must invoke the
1065 * high-latency rcu_barrier() function at module-unload time.
1066 *
1067 * The kfree_rcu() function handles this issue. In order to have a universal
1068 * callback function handling different offsets of rcu_head, the callback needs
1069 * to determine the starting address of the freed object, which can be a large
1070 * kmalloc or vmalloc allocation. To allow simply aligning the pointer down to
1071 * page boundary for those, only offsets up to 4095 bytes can be accommodated.
1072 * If the offset is larger than 4095 bytes, a compile-time error will
1073 * be generated in kvfree_rcu_arg_2(). If this error is triggered, you can
1074 * either fall back to use of call_rcu() or rearrange the structure to
1075 * position the rcu_head structure into the first 4096 bytes.
1076 *
1077 * The object to be freed can be allocated either by kmalloc(),
1078 * kmalloc_nolock(), or kmem_cache_alloc().
1079 *
1080 * Note that the allowable offset might decrease in the future.
1081 *
1082 * The BUILD_BUG_ON check must not involve any function calls, hence the
1083 * checks are done in macros here.
1084 */
1085#define kfree_rcu(ptr, rhf) kvfree_rcu_arg_2(ptr, rhf)
1086#define kvfree_rcu(ptr, rhf) kvfree_rcu_arg_2(ptr, rhf)
1087
1088/**
1089 * kfree_rcu_mightsleep() - kfree an object after a grace period.
1090 * @ptr: pointer to kfree for single-argument invocations.
1091 *
1092 * When it comes to head-less variant, only one argument
1093 * is passed and that is just a pointer which has to be
1094 * freed after a grace period. Therefore the semantic is
1095 *
1096 * kfree_rcu_mightsleep(ptr);
1097 *
1098 * where @ptr is the pointer to be freed by kvfree().
1099 *
1100 * Please note, head-less way of freeing is permitted to
1101 * use from a context that has to follow might_sleep()
1102 * annotation. Otherwise, please switch and embed the
1103 * rcu_head structure within the type of @ptr.
1104 */
1105#define kfree_rcu_mightsleep(ptr) kvfree_rcu_arg_1(ptr)
1106#define kvfree_rcu_mightsleep(ptr) kvfree_rcu_arg_1(ptr)
1107
1108/*
1109 * In mm/slab_common.c, no suitable header to include here.
1110 */
1111void kvfree_call_rcu(struct rcu_head *head, void *ptr);
1112
1113/*
1114 * The BUILD_BUG_ON() makes sure the rcu_head offset can be handled. See the
1115 * comment of kfree_rcu() for details.
1116 */
1117#define kvfree_rcu_arg_2(ptr, rhf) \
1118do { \
1119 typeof (ptr) ___p = (ptr); \
1120 \
1121 if (___p) { \
1122 BUILD_BUG_ON(offsetof(typeof(*(ptr)), rhf) >= 4096); \
1123 kvfree_call_rcu(&((___p)->rhf), (void *) (___p)); \
1124 } \
1125} while (0)
1126
1127#define kvfree_rcu_arg_1(ptr) \
1128do { \
1129 typeof(ptr) ___p = (ptr); \
1130 \
1131 if (___p) \
1132 kvfree_call_rcu(NULL, (void *) (___p)); \
1133} while (0)
1134
1135/*
1136 * Place this after a lock-acquisition primitive to guarantee that
1137 * an UNLOCK+LOCK pair acts as a full barrier. This guarantee applies
1138 * if the UNLOCK and LOCK are executed by the same CPU or if the
1139 * UNLOCK and LOCK operate on the same lock variable.
1140 */
1141#ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE
1142#define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */
1143#else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
1144#define smp_mb__after_unlock_lock() do { } while (0)
1145#endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
1146
1147
1148/* Has the specified rcu_head structure been handed to call_rcu()? */
1149
1150/**
1151 * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu()
1152 * @rhp: The rcu_head structure to initialize.
1153 *
1154 * If you intend to invoke rcu_head_after_call_rcu() to test whether a
1155 * given rcu_head structure has already been passed to call_rcu(), then
1156 * you must also invoke this rcu_head_init() function on it just after
1157 * allocating that structure. Calls to this function must not race with
1158 * calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation.
1159 */
1160static inline void rcu_head_init(struct rcu_head *rhp)
1161{
1162 rhp->func = (rcu_callback_t)~0L;
1163}
1164
1165/**
1166 * rcu_head_after_call_rcu() - Has this rcu_head been passed to call_rcu()?
1167 * @rhp: The rcu_head structure to test.
1168 * @f: The function passed to call_rcu() along with @rhp.
1169 *
1170 * Returns @true if the @rhp has been passed to call_rcu() with @func,
1171 * and @false otherwise. Emits a warning in any other case, including
1172 * the case where @rhp has already been invoked after a grace period.
1173 * Calls to this function must not race with callback invocation. One way
1174 * to avoid such races is to enclose the call to rcu_head_after_call_rcu()
1175 * in an RCU read-side critical section that includes a read-side fetch
1176 * of the pointer to the structure containing @rhp.
1177 */
1178static inline bool
1179rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f)
1180{
1181 rcu_callback_t func = READ_ONCE(rhp->func);
1182
1183 if (func == f)
1184 return true;
1185 WARN_ON_ONCE(func != (rcu_callback_t)~0L);
1186 return false;
1187}
1188
1189/* kernel/ksysfs.c definitions */
1190extern int rcu_expedited;
1191extern int rcu_normal;
1192
1193DEFINE_LOCK_GUARD_0(rcu, rcu_read_lock(), rcu_read_unlock())
1194DECLARE_LOCK_GUARD_0_ATTRS(rcu, __acquires_shared(RCU), __releases_shared(RCU))
1195
1196#endif /* __LINUX_RCUPDATE_H */