Line data Source code
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/preempt.h>
28 : #include <linux/bottom_half.h>
29 : #include <linux/lockdep.h>
30 : #include <asm/processor.h>
31 : #include <linux/cpumask.h>
32 : #include <linux/context_tracking_irq.h>
33 :
34 : #define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))
35 : #define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b))
36 : #define ulong2long(a) (*(long *)(&(a)))
37 : #define USHORT_CMP_GE(a, b) (USHRT_MAX / 2 >= (unsigned short)((a) - (b)))
38 : #define USHORT_CMP_LT(a, b) (USHRT_MAX / 2 < (unsigned short)((a) - (b)))
39 :
40 : /* Exported common interfaces */
41 : void call_rcu(struct rcu_head *head, rcu_callback_t func);
42 : void rcu_barrier_tasks(void);
43 : void rcu_barrier_tasks_rude(void);
44 : void synchronize_rcu(void);
45 :
46 : struct rcu_gp_oldstate;
47 : unsigned long get_completed_synchronize_rcu(void);
48 : void get_completed_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp);
49 :
50 : // Maximum number of unsigned long values corresponding to
51 : // not-yet-completed RCU grace periods.
52 : #define NUM_ACTIVE_RCU_POLL_OLDSTATE 2
53 :
54 : /**
55 : * same_state_synchronize_rcu - Are two old-state values identical?
56 : * @oldstate1: First old-state value.
57 : * @oldstate2: Second old-state value.
58 : *
59 : * The two old-state values must have been obtained from either
60 : * get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or
61 : * get_completed_synchronize_rcu(). Returns @true if the two values are
62 : * identical and @false otherwise. This allows structures whose lifetimes
63 : * are tracked by old-state values to push these values to a list header,
64 : * allowing those structures to be slightly smaller.
65 : */
66 : static inline bool same_state_synchronize_rcu(unsigned long oldstate1, unsigned long oldstate2)
67 : {
68 : return oldstate1 == oldstate2;
69 : }
70 :
71 : #ifdef CONFIG_PREEMPT_RCU
72 :
73 : void __rcu_read_lock(void);
74 : void __rcu_read_unlock(void);
75 :
76 : /*
77 : * Defined as a macro as it is a very low level header included from
78 : * areas that don't even know about current. This gives the rcu_read_lock()
79 : * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
80 : * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
81 : */
82 : #define rcu_preempt_depth() READ_ONCE(current->rcu_read_lock_nesting)
83 :
84 : #else /* #ifdef CONFIG_PREEMPT_RCU */
85 :
86 : #ifdef CONFIG_TINY_RCU
87 : #define rcu_read_unlock_strict() do { } while (0)
88 : #else
89 : void rcu_read_unlock_strict(void);
90 : #endif
91 :
92 : static inline void __rcu_read_lock(void)
93 : {
94 19294 : preempt_disable();
95 : }
96 :
97 : static inline void __rcu_read_unlock(void)
98 : {
99 19602 : preempt_enable();
100 : if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
101 : rcu_read_unlock_strict();
102 : }
103 :
104 : static inline int rcu_preempt_depth(void)
105 : {
106 : return 0;
107 : }
108 :
109 : #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
110 :
111 : #ifdef CONFIG_RCU_LAZY
112 : void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func);
113 : #else
114 0 : static inline void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func)
115 : {
116 0 : call_rcu(head, func);
117 0 : }
118 : #endif
119 :
120 : /* Internal to kernel */
121 : void rcu_init(void);
122 : extern int rcu_scheduler_active;
123 : void rcu_sched_clock_irq(int user);
124 : void rcu_report_dead(unsigned int cpu);
125 : void rcutree_migrate_callbacks(int cpu);
126 :
127 : #ifdef CONFIG_TASKS_RCU_GENERIC
128 : void rcu_init_tasks_generic(void);
129 : #else
130 : static inline void rcu_init_tasks_generic(void) { }
131 : #endif
132 :
133 : #ifdef CONFIG_RCU_STALL_COMMON
134 : void rcu_sysrq_start(void);
135 : void rcu_sysrq_end(void);
136 : #else /* #ifdef CONFIG_RCU_STALL_COMMON */
137 : static inline void rcu_sysrq_start(void) { }
138 : static inline void rcu_sysrq_end(void) { }
139 : #endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
140 :
141 : #if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK))
142 : void rcu_irq_work_resched(void);
143 : #else
144 : static inline void rcu_irq_work_resched(void) { }
145 : #endif
146 :
147 : #ifdef CONFIG_RCU_NOCB_CPU
148 : void rcu_init_nohz(void);
149 : int rcu_nocb_cpu_offload(int cpu);
150 : int rcu_nocb_cpu_deoffload(int cpu);
151 : void rcu_nocb_flush_deferred_wakeup(void);
152 : #else /* #ifdef CONFIG_RCU_NOCB_CPU */
153 : static inline void rcu_init_nohz(void) { }
154 : static inline int rcu_nocb_cpu_offload(int cpu) { return -EINVAL; }
155 : static inline int rcu_nocb_cpu_deoffload(int cpu) { return 0; }
156 : static inline void rcu_nocb_flush_deferred_wakeup(void) { }
157 : #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
158 :
159 : /**
160 : * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
161 : * @a: Code that RCU needs to pay attention to.
162 : *
163 : * RCU read-side critical sections are forbidden in the inner idle loop,
164 : * that is, between the ct_idle_enter() and the ct_idle_exit() -- RCU
165 : * will happily ignore any such read-side critical sections. However,
166 : * things like powertop need tracepoints in the inner idle loop.
167 : *
168 : * This macro provides the way out: RCU_NONIDLE(do_something_with_RCU())
169 : * will tell RCU that it needs to pay attention, invoke its argument
170 : * (in this example, calling the do_something_with_RCU() function),
171 : * and then tell RCU to go back to ignoring this CPU. It is permissible
172 : * to nest RCU_NONIDLE() wrappers, but not indefinitely (but the limit is
173 : * on the order of a million or so, even on 32-bit systems). It is
174 : * not legal to block within RCU_NONIDLE(), nor is it permissible to
175 : * transfer control either into or out of RCU_NONIDLE()'s statement.
176 : */
177 : #define RCU_NONIDLE(a) \
178 : do { \
179 : ct_irq_enter_irqson(); \
180 : do { a; } while (0); \
181 : ct_irq_exit_irqson(); \
182 : } while (0)
183 :
184 : /*
185 : * Note a quasi-voluntary context switch for RCU-tasks's benefit.
186 : * This is a macro rather than an inline function to avoid #include hell.
187 : */
188 : #ifdef CONFIG_TASKS_RCU_GENERIC
189 :
190 : # ifdef CONFIG_TASKS_RCU
191 : # define rcu_tasks_classic_qs(t, preempt) \
192 : do { \
193 : if (!(preempt) && READ_ONCE((t)->rcu_tasks_holdout)) \
194 : WRITE_ONCE((t)->rcu_tasks_holdout, false); \
195 : } while (0)
196 : void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
197 : void synchronize_rcu_tasks(void);
198 : # else
199 : # define rcu_tasks_classic_qs(t, preempt) do { } while (0)
200 : # define call_rcu_tasks call_rcu
201 : # define synchronize_rcu_tasks synchronize_rcu
202 : # endif
203 :
204 : # ifdef CONFIG_TASKS_TRACE_RCU
205 : // Bits for ->trc_reader_special.b.need_qs field.
206 : #define TRC_NEED_QS 0x1 // Task needs a quiescent state.
207 : #define TRC_NEED_QS_CHECKED 0x2 // Task has been checked for needing quiescent state.
208 :
209 : u8 rcu_trc_cmpxchg_need_qs(struct task_struct *t, u8 old, u8 new);
210 : void rcu_tasks_trace_qs_blkd(struct task_struct *t);
211 :
212 : # define rcu_tasks_trace_qs(t) \
213 : do { \
214 : int ___rttq_nesting = READ_ONCE((t)->trc_reader_nesting); \
215 : \
216 : if (likely(!READ_ONCE((t)->trc_reader_special.b.need_qs)) && \
217 : likely(!___rttq_nesting)) { \
218 : rcu_trc_cmpxchg_need_qs((t), 0, TRC_NEED_QS_CHECKED); \
219 : } else if (___rttq_nesting && ___rttq_nesting != INT_MIN && \
220 : !READ_ONCE((t)->trc_reader_special.b.blocked)) { \
221 : rcu_tasks_trace_qs_blkd(t); \
222 : } \
223 : } while (0)
224 : # else
225 : # define rcu_tasks_trace_qs(t) do { } while (0)
226 : # endif
227 :
228 : #define rcu_tasks_qs(t, preempt) \
229 : do { \
230 : rcu_tasks_classic_qs((t), (preempt)); \
231 : rcu_tasks_trace_qs(t); \
232 : } while (0)
233 :
234 : # ifdef CONFIG_TASKS_RUDE_RCU
235 : void call_rcu_tasks_rude(struct rcu_head *head, rcu_callback_t func);
236 : void synchronize_rcu_tasks_rude(void);
237 : # endif
238 :
239 : #define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t, false)
240 : void exit_tasks_rcu_start(void);
241 : void exit_tasks_rcu_stop(void);
242 : void exit_tasks_rcu_finish(void);
243 : #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
244 : #define rcu_tasks_classic_qs(t, preempt) do { } while (0)
245 : #define rcu_tasks_qs(t, preempt) do { } while (0)
246 : #define rcu_note_voluntary_context_switch(t) do { } while (0)
247 : #define call_rcu_tasks call_rcu
248 : #define synchronize_rcu_tasks synchronize_rcu
249 : static inline void exit_tasks_rcu_start(void) { }
250 : static inline void exit_tasks_rcu_stop(void) { }
251 : static inline void exit_tasks_rcu_finish(void) { }
252 : #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */
253 :
254 : /**
255 : * rcu_trace_implies_rcu_gp - does an RCU Tasks Trace grace period imply an RCU grace period?
256 : *
257 : * As an accident of implementation, an RCU Tasks Trace grace period also
258 : * acts as an RCU grace period. However, this could change at any time.
259 : * Code relying on this accident must call this function to verify that
260 : * this accident is still happening.
261 : *
262 : * You have been warned!
263 : */
264 : static inline bool rcu_trace_implies_rcu_gp(void) { return true; }
265 :
266 : /**
267 : * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU
268 : *
269 : * This macro resembles cond_resched(), except that it is defined to
270 : * report potential quiescent states to RCU-tasks even if the cond_resched()
271 : * machinery were to be shut off, as some advocate for PREEMPTION kernels.
272 : */
273 : #define cond_resched_tasks_rcu_qs() \
274 : do { \
275 : rcu_tasks_qs(current, false); \
276 : cond_resched(); \
277 : } while (0)
278 :
279 : /*
280 : * Infrastructure to implement the synchronize_() primitives in
281 : * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
282 : */
283 :
284 : #if defined(CONFIG_TREE_RCU)
285 : #include <linux/rcutree.h>
286 : #elif defined(CONFIG_TINY_RCU)
287 : #include <linux/rcutiny.h>
288 : #else
289 : #error "Unknown RCU implementation specified to kernel configuration"
290 : #endif
291 :
292 : /*
293 : * The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls
294 : * are needed for dynamic initialization and destruction of rcu_head
295 : * on the stack, and init_rcu_head()/destroy_rcu_head() are needed for
296 : * dynamic initialization and destruction of statically allocated rcu_head
297 : * structures. However, rcu_head structures allocated dynamically in the
298 : * heap don't need any initialization.
299 : */
300 : #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
301 : void init_rcu_head(struct rcu_head *head);
302 : void destroy_rcu_head(struct rcu_head *head);
303 : void init_rcu_head_on_stack(struct rcu_head *head);
304 : void destroy_rcu_head_on_stack(struct rcu_head *head);
305 : #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
306 : static inline void init_rcu_head(struct rcu_head *head) { }
307 : static inline void destroy_rcu_head(struct rcu_head *head) { }
308 : static inline void init_rcu_head_on_stack(struct rcu_head *head) { }
309 : static inline void destroy_rcu_head_on_stack(struct rcu_head *head) { }
310 : #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
311 :
312 : #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
313 : bool rcu_lockdep_current_cpu_online(void);
314 : #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
315 : static inline bool rcu_lockdep_current_cpu_online(void) { return true; }
316 : #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
317 :
318 : extern struct lockdep_map rcu_lock_map;
319 : extern struct lockdep_map rcu_bh_lock_map;
320 : extern struct lockdep_map rcu_sched_lock_map;
321 : extern struct lockdep_map rcu_callback_map;
322 :
323 : #ifdef CONFIG_DEBUG_LOCK_ALLOC
324 :
325 : static inline void rcu_lock_acquire(struct lockdep_map *map)
326 : {
327 : lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
328 : }
329 :
330 : static inline void rcu_lock_release(struct lockdep_map *map)
331 : {
332 : lock_release(map, _THIS_IP_);
333 : }
334 :
335 : int debug_lockdep_rcu_enabled(void);
336 : int rcu_read_lock_held(void);
337 : int rcu_read_lock_bh_held(void);
338 : int rcu_read_lock_sched_held(void);
339 : int rcu_read_lock_any_held(void);
340 :
341 : #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
342 :
343 : # define rcu_lock_acquire(a) do { } while (0)
344 : # define rcu_lock_release(a) do { } while (0)
345 :
346 : static inline int rcu_read_lock_held(void)
347 : {
348 : return 1;
349 : }
350 :
351 : static inline int rcu_read_lock_bh_held(void)
352 : {
353 : return 1;
354 : }
355 :
356 : static inline int rcu_read_lock_sched_held(void)
357 : {
358 : return !preemptible();
359 : }
360 :
361 : static inline int rcu_read_lock_any_held(void)
362 : {
363 : return !preemptible();
364 : }
365 :
366 : static inline int debug_lockdep_rcu_enabled(void)
367 : {
368 : return 0;
369 : }
370 :
371 : #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
372 :
373 : #ifdef CONFIG_PROVE_RCU
374 :
375 : /**
376 : * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met
377 : * @c: condition to check
378 : * @s: informative message
379 : *
380 : * This checks debug_lockdep_rcu_enabled() before checking (c) to
381 : * prevent early boot splats due to lockdep not yet being initialized,
382 : * and rechecks it after checking (c) to prevent false-positive splats
383 : * due to races with lockdep being disabled. See commit 3066820034b5dd
384 : * ("rcu: Reject RCU_LOCKDEP_WARN() false positives") for more detail.
385 : */
386 : #define RCU_LOCKDEP_WARN(c, s) \
387 : do { \
388 : static bool __section(".data.unlikely") __warned; \
389 : if (debug_lockdep_rcu_enabled() && (c) && \
390 : debug_lockdep_rcu_enabled() && !__warned) { \
391 : __warned = true; \
392 : lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
393 : } \
394 : } while (0)
395 :
396 : #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
397 : static inline void rcu_preempt_sleep_check(void)
398 : {
399 : RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
400 : "Illegal context switch in RCU read-side critical section");
401 : }
402 : #else /* #ifdef CONFIG_PROVE_RCU */
403 : static inline void rcu_preempt_sleep_check(void) { }
404 : #endif /* #else #ifdef CONFIG_PROVE_RCU */
405 :
406 : #define rcu_sleep_check() \
407 : do { \
408 : rcu_preempt_sleep_check(); \
409 : if (!IS_ENABLED(CONFIG_PREEMPT_RT)) \
410 : RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map), \
411 : "Illegal context switch in RCU-bh read-side critical section"); \
412 : RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), \
413 : "Illegal context switch in RCU-sched read-side critical section"); \
414 : } while (0)
415 :
416 : #else /* #ifdef CONFIG_PROVE_RCU */
417 :
418 : #define RCU_LOCKDEP_WARN(c, s) do { } while (0 && (c))
419 : #define rcu_sleep_check() do { } while (0)
420 :
421 : #endif /* #else #ifdef CONFIG_PROVE_RCU */
422 :
423 : /*
424 : * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
425 : * and rcu_assign_pointer(). Some of these could be folded into their
426 : * callers, but they are left separate in order to ease introduction of
427 : * multiple pointers markings to match different RCU implementations
428 : * (e.g., __srcu), should this make sense in the future.
429 : */
430 :
431 : #ifdef __CHECKER__
432 : #define rcu_check_sparse(p, space) \
433 : ((void)(((typeof(*p) space *)p) == p))
434 : #else /* #ifdef __CHECKER__ */
435 : #define rcu_check_sparse(p, space)
436 : #endif /* #else #ifdef __CHECKER__ */
437 :
438 : #define __unrcu_pointer(p, local) \
439 : ({ \
440 : typeof(*p) *local = (typeof(*p) *__force)(p); \
441 : rcu_check_sparse(p, __rcu); \
442 : ((typeof(*p) __force __kernel *)(local)); \
443 : })
444 : /**
445 : * unrcu_pointer - mark a pointer as not being RCU protected
446 : * @p: pointer needing to lose its __rcu property
447 : *
448 : * Converts @p from an __rcu pointer to a __kernel pointer.
449 : * This allows an __rcu pointer to be used with xchg() and friends.
450 : */
451 : #define unrcu_pointer(p) __unrcu_pointer(p, __UNIQUE_ID(rcu))
452 :
453 : #define __rcu_access_pointer(p, local, space) \
454 : ({ \
455 : typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \
456 : rcu_check_sparse(p, space); \
457 : ((typeof(*p) __force __kernel *)(local)); \
458 : })
459 : #define __rcu_dereference_check(p, local, c, space) \
460 : ({ \
461 : /* Dependency order vs. p above. */ \
462 : typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \
463 : RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
464 : rcu_check_sparse(p, space); \
465 : ((typeof(*p) __force __kernel *)(local)); \
466 : })
467 : #define __rcu_dereference_protected(p, local, c, space) \
468 : ({ \
469 : RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
470 : rcu_check_sparse(p, space); \
471 : ((typeof(*p) __force __kernel *)(p)); \
472 : })
473 : #define __rcu_dereference_raw(p, local) \
474 : ({ \
475 : /* Dependency order vs. p above. */ \
476 : typeof(p) local = READ_ONCE(p); \
477 : ((typeof(*p) __force __kernel *)(local)); \
478 : })
479 : #define rcu_dereference_raw(p) __rcu_dereference_raw(p, __UNIQUE_ID(rcu))
480 :
481 : /**
482 : * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
483 : * @v: The value to statically initialize with.
484 : */
485 : #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
486 :
487 : /**
488 : * rcu_assign_pointer() - assign to RCU-protected pointer
489 : * @p: pointer to assign to
490 : * @v: value to assign (publish)
491 : *
492 : * Assigns the specified value to the specified RCU-protected
493 : * pointer, ensuring that any concurrent RCU readers will see
494 : * any prior initialization.
495 : *
496 : * Inserts memory barriers on architectures that require them
497 : * (which is most of them), and also prevents the compiler from
498 : * reordering the code that initializes the structure after the pointer
499 : * assignment. More importantly, this call documents which pointers
500 : * will be dereferenced by RCU read-side code.
501 : *
502 : * In some special cases, you may use RCU_INIT_POINTER() instead
503 : * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due
504 : * to the fact that it does not constrain either the CPU or the compiler.
505 : * That said, using RCU_INIT_POINTER() when you should have used
506 : * rcu_assign_pointer() is a very bad thing that results in
507 : * impossible-to-diagnose memory corruption. So please be careful.
508 : * See the RCU_INIT_POINTER() comment header for details.
509 : *
510 : * Note that rcu_assign_pointer() evaluates each of its arguments only
511 : * once, appearances notwithstanding. One of the "extra" evaluations
512 : * is in typeof() and the other visible only to sparse (__CHECKER__),
513 : * neither of which actually execute the argument. As with most cpp
514 : * macros, this execute-arguments-only-once property is important, so
515 : * please be careful when making changes to rcu_assign_pointer() and the
516 : * other macros that it invokes.
517 : */
518 : #define rcu_assign_pointer(p, v) \
519 : do { \
520 : uintptr_t _r_a_p__v = (uintptr_t)(v); \
521 : rcu_check_sparse(p, __rcu); \
522 : \
523 : if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \
524 : WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \
525 : else \
526 : smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \
527 : } while (0)
528 :
529 : /**
530 : * rcu_replace_pointer() - replace an RCU pointer, returning its old value
531 : * @rcu_ptr: RCU pointer, whose old value is returned
532 : * @ptr: regular pointer
533 : * @c: the lockdep conditions under which the dereference will take place
534 : *
535 : * Perform a replacement, where @rcu_ptr is an RCU-annotated
536 : * pointer and @c is the lockdep argument that is passed to the
537 : * rcu_dereference_protected() call used to read that pointer. The old
538 : * value of @rcu_ptr is returned, and @rcu_ptr is set to @ptr.
539 : */
540 : #define rcu_replace_pointer(rcu_ptr, ptr, c) \
541 : ({ \
542 : typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c)); \
543 : rcu_assign_pointer((rcu_ptr), (ptr)); \
544 : __tmp; \
545 : })
546 :
547 : /**
548 : * rcu_access_pointer() - fetch RCU pointer with no dereferencing
549 : * @p: The pointer to read
550 : *
551 : * Return the value of the specified RCU-protected pointer, but omit the
552 : * lockdep checks for being in an RCU read-side critical section. This is
553 : * useful when the value of this pointer is accessed, but the pointer is
554 : * not dereferenced, for example, when testing an RCU-protected pointer
555 : * against NULL. Although rcu_access_pointer() may also be used in cases
556 : * where update-side locks prevent the value of the pointer from changing,
557 : * you should instead use rcu_dereference_protected() for this use case.
558 : * Within an RCU read-side critical section, there is little reason to
559 : * use rcu_access_pointer().
560 : *
561 : * It is usually best to test the rcu_access_pointer() return value
562 : * directly in order to avoid accidental dereferences being introduced
563 : * by later inattentive changes. In other words, assigning the
564 : * rcu_access_pointer() return value to a local variable results in an
565 : * accident waiting to happen.
566 : *
567 : * It is also permissible to use rcu_access_pointer() when read-side
568 : * access to the pointer was removed at least one grace period ago, as is
569 : * the case in the context of the RCU callback that is freeing up the data,
570 : * or after a synchronize_rcu() returns. This can be useful when tearing
571 : * down multi-linked structures after a grace period has elapsed. However,
572 : * rcu_dereference_protected() is normally preferred for this use case.
573 : */
574 : #define rcu_access_pointer(p) __rcu_access_pointer((p), __UNIQUE_ID(rcu), __rcu)
575 :
576 : /**
577 : * rcu_dereference_check() - rcu_dereference with debug checking
578 : * @p: The pointer to read, prior to dereferencing
579 : * @c: The conditions under which the dereference will take place
580 : *
581 : * Do an rcu_dereference(), but check that the conditions under which the
582 : * dereference will take place are correct. Typically the conditions
583 : * indicate the various locking conditions that should be held at that
584 : * point. The check should return true if the conditions are satisfied.
585 : * An implicit check for being in an RCU read-side critical section
586 : * (rcu_read_lock()) is included.
587 : *
588 : * For example:
589 : *
590 : * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
591 : *
592 : * could be used to indicate to lockdep that foo->bar may only be dereferenced
593 : * if either rcu_read_lock() is held, or that the lock required to replace
594 : * the bar struct at foo->bar is held.
595 : *
596 : * Note that the list of conditions may also include indications of when a lock
597 : * need not be held, for example during initialisation or destruction of the
598 : * target struct:
599 : *
600 : * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
601 : * atomic_read(&foo->usage) == 0);
602 : *
603 : * Inserts memory barriers on architectures that require them
604 : * (currently only the Alpha), prevents the compiler from refetching
605 : * (and from merging fetches), and, more importantly, documents exactly
606 : * which pointers are protected by RCU and checks that the pointer is
607 : * annotated as __rcu.
608 : */
609 : #define rcu_dereference_check(p, c) \
610 : __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
611 : (c) || rcu_read_lock_held(), __rcu)
612 :
613 : /**
614 : * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
615 : * @p: The pointer to read, prior to dereferencing
616 : * @c: The conditions under which the dereference will take place
617 : *
618 : * This is the RCU-bh counterpart to rcu_dereference_check(). However,
619 : * please note that starting in v5.0 kernels, vanilla RCU grace periods
620 : * wait for local_bh_disable() regions of code in addition to regions of
621 : * code demarked by rcu_read_lock() and rcu_read_unlock(). This means
622 : * that synchronize_rcu(), call_rcu, and friends all take not only
623 : * rcu_read_lock() but also rcu_read_lock_bh() into account.
624 : */
625 : #define rcu_dereference_bh_check(p, c) \
626 : __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
627 : (c) || rcu_read_lock_bh_held(), __rcu)
628 :
629 : /**
630 : * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
631 : * @p: The pointer to read, prior to dereferencing
632 : * @c: The conditions under which the dereference will take place
633 : *
634 : * This is the RCU-sched counterpart to rcu_dereference_check().
635 : * However, please note that starting in v5.0 kernels, vanilla RCU grace
636 : * periods wait for preempt_disable() regions of code in addition to
637 : * regions of code demarked by rcu_read_lock() and rcu_read_unlock().
638 : * This means that synchronize_rcu(), call_rcu, and friends all take not
639 : * only rcu_read_lock() but also rcu_read_lock_sched() into account.
640 : */
641 : #define rcu_dereference_sched_check(p, c) \
642 : __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
643 : (c) || rcu_read_lock_sched_held(), \
644 : __rcu)
645 :
646 : /*
647 : * The tracing infrastructure traces RCU (we want that), but unfortunately
648 : * some of the RCU checks causes tracing to lock up the system.
649 : *
650 : * The no-tracing version of rcu_dereference_raw() must not call
651 : * rcu_read_lock_held().
652 : */
653 : #define rcu_dereference_raw_check(p) \
654 : __rcu_dereference_check((p), __UNIQUE_ID(rcu), 1, __rcu)
655 :
656 : /**
657 : * rcu_dereference_protected() - fetch RCU pointer when updates prevented
658 : * @p: The pointer to read, prior to dereferencing
659 : * @c: The conditions under which the dereference will take place
660 : *
661 : * Return the value of the specified RCU-protected pointer, but omit
662 : * the READ_ONCE(). This is useful in cases where update-side locks
663 : * prevent the value of the pointer from changing. Please note that this
664 : * primitive does *not* prevent the compiler from repeating this reference
665 : * or combining it with other references, so it should not be used without
666 : * protection of appropriate locks.
667 : *
668 : * This function is only for update-side use. Using this function
669 : * when protected only by rcu_read_lock() will result in infrequent
670 : * but very ugly failures.
671 : */
672 : #define rcu_dereference_protected(p, c) \
673 : __rcu_dereference_protected((p), __UNIQUE_ID(rcu), (c), __rcu)
674 :
675 :
676 : /**
677 : * rcu_dereference() - fetch RCU-protected pointer for dereferencing
678 : * @p: The pointer to read, prior to dereferencing
679 : *
680 : * This is a simple wrapper around rcu_dereference_check().
681 : */
682 : #define rcu_dereference(p) rcu_dereference_check(p, 0)
683 :
684 : /**
685 : * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
686 : * @p: The pointer to read, prior to dereferencing
687 : *
688 : * Makes rcu_dereference_check() do the dirty work.
689 : */
690 : #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
691 :
692 : /**
693 : * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
694 : * @p: The pointer to read, prior to dereferencing
695 : *
696 : * Makes rcu_dereference_check() do the dirty work.
697 : */
698 : #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
699 :
700 : /**
701 : * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism
702 : * @p: The pointer to hand off
703 : *
704 : * This is simply an identity function, but it documents where a pointer
705 : * is handed off from RCU to some other synchronization mechanism, for
706 : * example, reference counting or locking. In C11, it would map to
707 : * kill_dependency(). It could be used as follows::
708 : *
709 : * rcu_read_lock();
710 : * p = rcu_dereference(gp);
711 : * long_lived = is_long_lived(p);
712 : * if (long_lived) {
713 : * if (!atomic_inc_not_zero(p->refcnt))
714 : * long_lived = false;
715 : * else
716 : * p = rcu_pointer_handoff(p);
717 : * }
718 : * rcu_read_unlock();
719 : */
720 : #define rcu_pointer_handoff(p) (p)
721 :
722 : /**
723 : * rcu_read_lock() - mark the beginning of an RCU read-side critical section
724 : *
725 : * When synchronize_rcu() is invoked on one CPU while other CPUs
726 : * are within RCU read-side critical sections, then the
727 : * synchronize_rcu() is guaranteed to block until after all the other
728 : * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
729 : * on one CPU while other CPUs are within RCU read-side critical
730 : * sections, invocation of the corresponding RCU callback is deferred
731 : * until after the all the other CPUs exit their critical sections.
732 : *
733 : * In v5.0 and later kernels, synchronize_rcu() and call_rcu() also
734 : * wait for regions of code with preemption disabled, including regions of
735 : * code with interrupts or softirqs disabled. In pre-v5.0 kernels, which
736 : * define synchronize_sched(), only code enclosed within rcu_read_lock()
737 : * and rcu_read_unlock() are guaranteed to be waited for.
738 : *
739 : * Note, however, that RCU callbacks are permitted to run concurrently
740 : * with new RCU read-side critical sections. One way that this can happen
741 : * is via the following sequence of events: (1) CPU 0 enters an RCU
742 : * read-side critical section, (2) CPU 1 invokes call_rcu() to register
743 : * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
744 : * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
745 : * callback is invoked. This is legal, because the RCU read-side critical
746 : * section that was running concurrently with the call_rcu() (and which
747 : * therefore might be referencing something that the corresponding RCU
748 : * callback would free up) has completed before the corresponding
749 : * RCU callback is invoked.
750 : *
751 : * RCU read-side critical sections may be nested. Any deferred actions
752 : * will be deferred until the outermost RCU read-side critical section
753 : * completes.
754 : *
755 : * You can avoid reading and understanding the next paragraph by
756 : * following this rule: don't put anything in an rcu_read_lock() RCU
757 : * read-side critical section that would block in a !PREEMPTION kernel.
758 : * But if you want the full story, read on!
759 : *
760 : * In non-preemptible RCU implementations (pure TREE_RCU and TINY_RCU),
761 : * it is illegal to block while in an RCU read-side critical section.
762 : * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPTION
763 : * kernel builds, RCU read-side critical sections may be preempted,
764 : * but explicit blocking is illegal. Finally, in preemptible RCU
765 : * implementations in real-time (with -rt patchset) kernel builds, RCU
766 : * read-side critical sections may be preempted and they may also block, but
767 : * only when acquiring spinlocks that are subject to priority inheritance.
768 : */
769 : static __always_inline void rcu_read_lock(void)
770 : {
771 : __rcu_read_lock();
772 : __acquire(RCU);
773 : rcu_lock_acquire(&rcu_lock_map);
774 : RCU_LOCKDEP_WARN(!rcu_is_watching(),
775 : "rcu_read_lock() used illegally while idle");
776 : }
777 :
778 : /*
779 : * So where is rcu_write_lock()? It does not exist, as there is no
780 : * way for writers to lock out RCU readers. This is a feature, not
781 : * a bug -- this property is what provides RCU's performance benefits.
782 : * Of course, writers must coordinate with each other. The normal
783 : * spinlock primitives work well for this, but any other technique may be
784 : * used as well. RCU does not care how the writers keep out of each
785 : * others' way, as long as they do so.
786 : */
787 :
788 : /**
789 : * rcu_read_unlock() - marks the end of an RCU read-side critical section.
790 : *
791 : * In almost all situations, rcu_read_unlock() is immune from deadlock.
792 : * In recent kernels that have consolidated synchronize_sched() and
793 : * synchronize_rcu_bh() into synchronize_rcu(), this deadlock immunity
794 : * also extends to the scheduler's runqueue and priority-inheritance
795 : * spinlocks, courtesy of the quiescent-state deferral that is carried
796 : * out when rcu_read_unlock() is invoked with interrupts disabled.
797 : *
798 : * See rcu_read_lock() for more information.
799 : */
800 : static inline void rcu_read_unlock(void)
801 : {
802 : RCU_LOCKDEP_WARN(!rcu_is_watching(),
803 : "rcu_read_unlock() used illegally while idle");
804 : __release(RCU);
805 : __rcu_read_unlock();
806 : rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
807 : }
808 :
809 : /**
810 : * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
811 : *
812 : * This is equivalent to rcu_read_lock(), but also disables softirqs.
813 : * Note that anything else that disables softirqs can also serve as an RCU
814 : * read-side critical section. However, please note that this equivalence
815 : * applies only to v5.0 and later. Before v5.0, rcu_read_lock() and
816 : * rcu_read_lock_bh() were unrelated.
817 : *
818 : * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
819 : * must occur in the same context, for example, it is illegal to invoke
820 : * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
821 : * was invoked from some other task.
822 : */
823 : static inline void rcu_read_lock_bh(void)
824 : {
825 : local_bh_disable();
826 : __acquire(RCU_BH);
827 : rcu_lock_acquire(&rcu_bh_lock_map);
828 : RCU_LOCKDEP_WARN(!rcu_is_watching(),
829 : "rcu_read_lock_bh() used illegally while idle");
830 : }
831 :
832 : /**
833 : * rcu_read_unlock_bh() - marks the end of a softirq-only RCU critical section
834 : *
835 : * See rcu_read_lock_bh() for more information.
836 : */
837 : static inline void rcu_read_unlock_bh(void)
838 : {
839 : RCU_LOCKDEP_WARN(!rcu_is_watching(),
840 : "rcu_read_unlock_bh() used illegally while idle");
841 : rcu_lock_release(&rcu_bh_lock_map);
842 : __release(RCU_BH);
843 : local_bh_enable();
844 : }
845 :
846 : /**
847 : * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
848 : *
849 : * This is equivalent to rcu_read_lock(), but also disables preemption.
850 : * Read-side critical sections can also be introduced by anything else that
851 : * disables preemption, including local_irq_disable() and friends. However,
852 : * please note that the equivalence to rcu_read_lock() applies only to
853 : * v5.0 and later. Before v5.0, rcu_read_lock() and rcu_read_lock_sched()
854 : * were unrelated.
855 : *
856 : * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
857 : * must occur in the same context, for example, it is illegal to invoke
858 : * rcu_read_unlock_sched() from process context if the matching
859 : * rcu_read_lock_sched() was invoked from an NMI handler.
860 : */
861 : static inline void rcu_read_lock_sched(void)
862 : {
863 0 : preempt_disable();
864 : __acquire(RCU_SCHED);
865 : rcu_lock_acquire(&rcu_sched_lock_map);
866 : RCU_LOCKDEP_WARN(!rcu_is_watching(),
867 : "rcu_read_lock_sched() used illegally while idle");
868 : }
869 :
870 : /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
871 : static inline notrace void rcu_read_lock_sched_notrace(void)
872 : {
873 : preempt_disable_notrace();
874 : __acquire(RCU_SCHED);
875 : }
876 :
877 : /**
878 : * rcu_read_unlock_sched() - marks the end of a RCU-classic critical section
879 : *
880 : * See rcu_read_lock_sched() for more information.
881 : */
882 : static inline void rcu_read_unlock_sched(void)
883 : {
884 : RCU_LOCKDEP_WARN(!rcu_is_watching(),
885 : "rcu_read_unlock_sched() used illegally while idle");
886 : rcu_lock_release(&rcu_sched_lock_map);
887 : __release(RCU_SCHED);
888 0 : preempt_enable();
889 : }
890 :
891 : /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
892 : static inline notrace void rcu_read_unlock_sched_notrace(void)
893 : {
894 : __release(RCU_SCHED);
895 : preempt_enable_notrace();
896 : }
897 :
898 : /**
899 : * RCU_INIT_POINTER() - initialize an RCU protected pointer
900 : * @p: The pointer to be initialized.
901 : * @v: The value to initialized the pointer to.
902 : *
903 : * Initialize an RCU-protected pointer in special cases where readers
904 : * do not need ordering constraints on the CPU or the compiler. These
905 : * special cases are:
906 : *
907 : * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer *or*
908 : * 2. The caller has taken whatever steps are required to prevent
909 : * RCU readers from concurrently accessing this pointer *or*
910 : * 3. The referenced data structure has already been exposed to
911 : * readers either at compile time or via rcu_assign_pointer() *and*
912 : *
913 : * a. You have not made *any* reader-visible changes to
914 : * this structure since then *or*
915 : * b. It is OK for readers accessing this structure from its
916 : * new location to see the old state of the structure. (For
917 : * example, the changes were to statistical counters or to
918 : * other state where exact synchronization is not required.)
919 : *
920 : * Failure to follow these rules governing use of RCU_INIT_POINTER() will
921 : * result in impossible-to-diagnose memory corruption. As in the structures
922 : * will look OK in crash dumps, but any concurrent RCU readers might
923 : * see pre-initialized values of the referenced data structure. So
924 : * please be very careful how you use RCU_INIT_POINTER()!!!
925 : *
926 : * If you are creating an RCU-protected linked structure that is accessed
927 : * by a single external-to-structure RCU-protected pointer, then you may
928 : * use RCU_INIT_POINTER() to initialize the internal RCU-protected
929 : * pointers, but you must use rcu_assign_pointer() to initialize the
930 : * external-to-structure pointer *after* you have completely initialized
931 : * the reader-accessible portions of the linked structure.
932 : *
933 : * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
934 : * ordering guarantees for either the CPU or the compiler.
935 : */
936 : #define RCU_INIT_POINTER(p, v) \
937 : do { \
938 : rcu_check_sparse(p, __rcu); \
939 : WRITE_ONCE(p, RCU_INITIALIZER(v)); \
940 : } while (0)
941 :
942 : /**
943 : * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
944 : * @p: The pointer to be initialized.
945 : * @v: The value to initialized the pointer to.
946 : *
947 : * GCC-style initialization for an RCU-protected pointer in a structure field.
948 : */
949 : #define RCU_POINTER_INITIALIZER(p, v) \
950 : .p = RCU_INITIALIZER(v)
951 :
952 : /*
953 : * Does the specified offset indicate that the corresponding rcu_head
954 : * structure can be handled by kvfree_rcu()?
955 : */
956 : #define __is_kvfree_rcu_offset(offset) ((offset) < 4096)
957 :
958 : /**
959 : * kfree_rcu() - kfree an object after a grace period.
960 : * @ptr: pointer to kfree for both single- and double-argument invocations.
961 : * @rhf: the name of the struct rcu_head within the type of @ptr,
962 : * but only for double-argument invocations.
963 : *
964 : * Many rcu callbacks functions just call kfree() on the base structure.
965 : * These functions are trivial, but their size adds up, and furthermore
966 : * when they are used in a kernel module, that module must invoke the
967 : * high-latency rcu_barrier() function at module-unload time.
968 : *
969 : * The kfree_rcu() function handles this issue. Rather than encoding a
970 : * function address in the embedded rcu_head structure, kfree_rcu() instead
971 : * encodes the offset of the rcu_head structure within the base structure.
972 : * Because the functions are not allowed in the low-order 4096 bytes of
973 : * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
974 : * If the offset is larger than 4095 bytes, a compile-time error will
975 : * be generated in kvfree_rcu_arg_2(). If this error is triggered, you can
976 : * either fall back to use of call_rcu() or rearrange the structure to
977 : * position the rcu_head structure into the first 4096 bytes.
978 : *
979 : * Note that the allowable offset might decrease in the future, for example,
980 : * to allow something like kmem_cache_free_rcu().
981 : *
982 : * The BUILD_BUG_ON check must not involve any function calls, hence the
983 : * checks are done in macros here.
984 : */
985 : #define kfree_rcu(ptr, rhf...) kvfree_rcu(ptr, ## rhf)
986 :
987 : /**
988 : * kvfree_rcu() - kvfree an object after a grace period.
989 : *
990 : * This macro consists of one or two arguments and it is
991 : * based on whether an object is head-less or not. If it
992 : * has a head then a semantic stays the same as it used
993 : * to be before:
994 : *
995 : * kvfree_rcu(ptr, rhf);
996 : *
997 : * where @ptr is a pointer to kvfree(), @rhf is the name
998 : * of the rcu_head structure within the type of @ptr.
999 : *
1000 : * When it comes to head-less variant, only one argument
1001 : * is passed and that is just a pointer which has to be
1002 : * freed after a grace period. Therefore the semantic is
1003 : *
1004 : * kvfree_rcu(ptr);
1005 : *
1006 : * where @ptr is the pointer to be freed by kvfree().
1007 : *
1008 : * Please note, head-less way of freeing is permitted to
1009 : * use from a context that has to follow might_sleep()
1010 : * annotation. Otherwise, please switch and embed the
1011 : * rcu_head structure within the type of @ptr.
1012 : */
1013 : #define kvfree_rcu(...) KVFREE_GET_MACRO(__VA_ARGS__, \
1014 : kvfree_rcu_arg_2, kvfree_rcu_arg_1)(__VA_ARGS__)
1015 :
1016 : #define kvfree_rcu_mightsleep(ptr) kvfree_rcu_arg_1(ptr)
1017 : #define kfree_rcu_mightsleep(ptr) kvfree_rcu_mightsleep(ptr)
1018 :
1019 : #define KVFREE_GET_MACRO(_1, _2, NAME, ...) NAME
1020 : #define kvfree_rcu_arg_2(ptr, rhf) \
1021 : do { \
1022 : typeof (ptr) ___p = (ptr); \
1023 : \
1024 : if (___p) { \
1025 : BUILD_BUG_ON(!__is_kvfree_rcu_offset(offsetof(typeof(*(ptr)), rhf))); \
1026 : kvfree_call_rcu(&((___p)->rhf), (void *) (___p)); \
1027 : } \
1028 : } while (0)
1029 :
1030 : #define kvfree_rcu_arg_1(ptr) \
1031 : do { \
1032 : typeof(ptr) ___p = (ptr); \
1033 : \
1034 : if (___p) \
1035 : kvfree_call_rcu(NULL, (void *) (___p)); \
1036 : } while (0)
1037 :
1038 : /*
1039 : * Place this after a lock-acquisition primitive to guarantee that
1040 : * an UNLOCK+LOCK pair acts as a full barrier. This guarantee applies
1041 : * if the UNLOCK and LOCK are executed by the same CPU or if the
1042 : * UNLOCK and LOCK operate on the same lock variable.
1043 : */
1044 : #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE
1045 : #define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */
1046 : #else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
1047 : #define smp_mb__after_unlock_lock() do { } while (0)
1048 : #endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
1049 :
1050 :
1051 : /* Has the specified rcu_head structure been handed to call_rcu()? */
1052 :
1053 : /**
1054 : * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu()
1055 : * @rhp: The rcu_head structure to initialize.
1056 : *
1057 : * If you intend to invoke rcu_head_after_call_rcu() to test whether a
1058 : * given rcu_head structure has already been passed to call_rcu(), then
1059 : * you must also invoke this rcu_head_init() function on it just after
1060 : * allocating that structure. Calls to this function must not race with
1061 : * calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation.
1062 : */
1063 : static inline void rcu_head_init(struct rcu_head *rhp)
1064 : {
1065 0 : rhp->func = (rcu_callback_t)~0L;
1066 : }
1067 :
1068 : /**
1069 : * rcu_head_after_call_rcu() - Has this rcu_head been passed to call_rcu()?
1070 : * @rhp: The rcu_head structure to test.
1071 : * @f: The function passed to call_rcu() along with @rhp.
1072 : *
1073 : * Returns @true if the @rhp has been passed to call_rcu() with @func,
1074 : * and @false otherwise. Emits a warning in any other case, including
1075 : * the case where @rhp has already been invoked after a grace period.
1076 : * Calls to this function must not race with callback invocation. One way
1077 : * to avoid such races is to enclose the call to rcu_head_after_call_rcu()
1078 : * in an RCU read-side critical section that includes a read-side fetch
1079 : * of the pointer to the structure containing @rhp.
1080 : */
1081 : static inline bool
1082 0 : rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f)
1083 : {
1084 0 : rcu_callback_t func = READ_ONCE(rhp->func);
1085 :
1086 0 : if (func == f)
1087 : return true;
1088 0 : WARN_ON_ONCE(func != (rcu_callback_t)~0L);
1089 : return false;
1090 : }
1091 :
1092 : /* kernel/ksysfs.c definitions */
1093 : extern int rcu_expedited;
1094 : extern int rcu_normal;
1095 :
1096 : #endif /* __LINUX_RCUPDATE_H */
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