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Linux/include/linux/rcupdate.h

  1 /*
  2  * Read-Copy Update mechanism for mutual exclusion
  3  *
  4  * This program is free software; you can redistribute it and/or modify
  5  * it under the terms of the GNU General Public License as published by
  6  * the Free Software Foundation; either version 2 of the License, or
  7  * (at your option) any later version.
  8  *
  9  * This program is distributed in the hope that it will be useful,
 10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
 11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 12  * GNU General Public License for more details.
 13  *
 14  * You should have received a copy of the GNU General Public License
 15  * along with this program; if not, you can access it online at
 16  * http://www.gnu.org/licenses/gpl-2.0.html.
 17  *
 18  * Copyright IBM Corporation, 2001
 19  *
 20  * Author: Dipankar Sarma <dipankar@in.ibm.com>
 21  *
 22  * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
 23  * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
 24  * Papers:
 25  * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
 26  * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
 27  *
 28  * For detailed explanation of Read-Copy Update mechanism see -
 29  *              http://lse.sourceforge.net/locking/rcupdate.html
 30  *
 31  */
 32 
 33 #ifndef __LINUX_RCUPDATE_H
 34 #define __LINUX_RCUPDATE_H
 35 
 36 #include <linux/types.h>
 37 #include <linux/cache.h>
 38 #include <linux/spinlock.h>
 39 #include <linux/threads.h>
 40 #include <linux/cpumask.h>
 41 #include <linux/seqlock.h>
 42 #include <linux/lockdep.h>
 43 #include <linux/completion.h>
 44 #include <linux/debugobjects.h>
 45 #include <linux/bug.h>
 46 #include <linux/compiler.h>
 47 #include <linux/ktime.h>
 48 
 49 #include <asm/barrier.h>
 50 
 51 #ifndef CONFIG_TINY_RCU
 52 extern int rcu_expedited; /* for sysctl */
 53 extern int rcu_normal;    /* also for sysctl */
 54 #endif /* #ifndef CONFIG_TINY_RCU */
 55 
 56 #ifdef CONFIG_TINY_RCU
 57 /* Tiny RCU doesn't expedite, as its purpose in life is instead to be tiny. */
 58 static inline bool rcu_gp_is_normal(void)  /* Internal RCU use. */
 59 {
 60         return true;
 61 }
 62 static inline bool rcu_gp_is_expedited(void)  /* Internal RCU use. */
 63 {
 64         return false;
 65 }
 66 
 67 static inline void rcu_expedite_gp(void)
 68 {
 69 }
 70 
 71 static inline void rcu_unexpedite_gp(void)
 72 {
 73 }
 74 #else /* #ifdef CONFIG_TINY_RCU */
 75 bool rcu_gp_is_normal(void);     /* Internal RCU use. */
 76 bool rcu_gp_is_expedited(void);  /* Internal RCU use. */
 77 void rcu_expedite_gp(void);
 78 void rcu_unexpedite_gp(void);
 79 #endif /* #else #ifdef CONFIG_TINY_RCU */
 80 
 81 enum rcutorture_type {
 82         RCU_FLAVOR,
 83         RCU_BH_FLAVOR,
 84         RCU_SCHED_FLAVOR,
 85         RCU_TASKS_FLAVOR,
 86         SRCU_FLAVOR,
 87         INVALID_RCU_FLAVOR
 88 };
 89 
 90 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
 91 void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
 92                             unsigned long *gpnum, unsigned long *completed);
 93 void rcutorture_record_test_transition(void);
 94 void rcutorture_record_progress(unsigned long vernum);
 95 void do_trace_rcu_torture_read(const char *rcutorturename,
 96                                struct rcu_head *rhp,
 97                                unsigned long secs,
 98                                unsigned long c_old,
 99                                unsigned long c);
100 #else
101 static inline void rcutorture_get_gp_data(enum rcutorture_type test_type,
102                                           int *flags,
103                                           unsigned long *gpnum,
104                                           unsigned long *completed)
105 {
106         *flags = 0;
107         *gpnum = 0;
108         *completed = 0;
109 }
110 static inline void rcutorture_record_test_transition(void)
111 {
112 }
113 static inline void rcutorture_record_progress(unsigned long vernum)
114 {
115 }
116 #ifdef CONFIG_RCU_TRACE
117 void do_trace_rcu_torture_read(const char *rcutorturename,
118                                struct rcu_head *rhp,
119                                unsigned long secs,
120                                unsigned long c_old,
121                                unsigned long c);
122 #else
123 #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
124         do { } while (0)
125 #endif
126 #endif
127 
128 #define UINT_CMP_GE(a, b)       (UINT_MAX / 2 >= (a) - (b))
129 #define UINT_CMP_LT(a, b)       (UINT_MAX / 2 < (a) - (b))
130 #define ULONG_CMP_GE(a, b)      (ULONG_MAX / 2 >= (a) - (b))
131 #define ULONG_CMP_LT(a, b)      (ULONG_MAX / 2 < (a) - (b))
132 #define ulong2long(a)           (*(long *)(&(a)))
133 
134 /* Exported common interfaces */
135 
136 #ifdef CONFIG_PREEMPT_RCU
137 
138 /**
139  * call_rcu() - Queue an RCU callback for invocation after a grace period.
140  * @head: structure to be used for queueing the RCU updates.
141  * @func: actual callback function to be invoked after the grace period
142  *
143  * The callback function will be invoked some time after a full grace
144  * period elapses, in other words after all pre-existing RCU read-side
145  * critical sections have completed.  However, the callback function
146  * might well execute concurrently with RCU read-side critical sections
147  * that started after call_rcu() was invoked.  RCU read-side critical
148  * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
149  * and may be nested.
150  *
151  * Note that all CPUs must agree that the grace period extended beyond
152  * all pre-existing RCU read-side critical section.  On systems with more
153  * than one CPU, this means that when "func()" is invoked, each CPU is
154  * guaranteed to have executed a full memory barrier since the end of its
155  * last RCU read-side critical section whose beginning preceded the call
156  * to call_rcu().  It also means that each CPU executing an RCU read-side
157  * critical section that continues beyond the start of "func()" must have
158  * executed a memory barrier after the call_rcu() but before the beginning
159  * of that RCU read-side critical section.  Note that these guarantees
160  * include CPUs that are offline, idle, or executing in user mode, as
161  * well as CPUs that are executing in the kernel.
162  *
163  * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
164  * resulting RCU callback function "func()", then both CPU A and CPU B are
165  * guaranteed to execute a full memory barrier during the time interval
166  * between the call to call_rcu() and the invocation of "func()" -- even
167  * if CPU A and CPU B are the same CPU (but again only if the system has
168  * more than one CPU).
169  */
170 void call_rcu(struct rcu_head *head,
171               rcu_callback_t func);
172 
173 #else /* #ifdef CONFIG_PREEMPT_RCU */
174 
175 /* In classic RCU, call_rcu() is just call_rcu_sched(). */
176 #define call_rcu        call_rcu_sched
177 
178 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
179 
180 /**
181  * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
182  * @head: structure to be used for queueing the RCU updates.
183  * @func: actual callback function to be invoked after the grace period
184  *
185  * The callback function will be invoked some time after a full grace
186  * period elapses, in other words after all currently executing RCU
187  * read-side critical sections have completed. call_rcu_bh() assumes
188  * that the read-side critical sections end on completion of a softirq
189  * handler. This means that read-side critical sections in process
190  * context must not be interrupted by softirqs. This interface is to be
191  * used when most of the read-side critical sections are in softirq context.
192  * RCU read-side critical sections are delimited by :
193  *  - rcu_read_lock() and  rcu_read_unlock(), if in interrupt context.
194  *  OR
195  *  - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
196  *  These may be nested.
197  *
198  * See the description of call_rcu() for more detailed information on
199  * memory ordering guarantees.
200  */
201 void call_rcu_bh(struct rcu_head *head,
202                  rcu_callback_t func);
203 
204 /**
205  * call_rcu_sched() - Queue an RCU for invocation after sched grace period.
206  * @head: structure to be used for queueing the RCU updates.
207  * @func: actual callback function to be invoked after the grace period
208  *
209  * The callback function will be invoked some time after a full grace
210  * period elapses, in other words after all currently executing RCU
211  * read-side critical sections have completed. call_rcu_sched() assumes
212  * that the read-side critical sections end on enabling of preemption
213  * or on voluntary preemption.
214  * RCU read-side critical sections are delimited by :
215  *  - rcu_read_lock_sched() and  rcu_read_unlock_sched(),
216  *  OR
217  *  anything that disables preemption.
218  *  These may be nested.
219  *
220  * See the description of call_rcu() for more detailed information on
221  * memory ordering guarantees.
222  */
223 void call_rcu_sched(struct rcu_head *head,
224                     rcu_callback_t func);
225 
226 void synchronize_sched(void);
227 
228 /*
229  * Structure allowing asynchronous waiting on RCU.
230  */
231 struct rcu_synchronize {
232         struct rcu_head head;
233         struct completion completion;
234 };
235 void wakeme_after_rcu(struct rcu_head *head);
236 
237 void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
238                    struct rcu_synchronize *rs_array);
239 
240 #define _wait_rcu_gp(checktiny, ...) \
241 do {                                                                    \
242         call_rcu_func_t __crcu_array[] = { __VA_ARGS__ };               \
243         struct rcu_synchronize __rs_array[ARRAY_SIZE(__crcu_array)];    \
244         __wait_rcu_gp(checktiny, ARRAY_SIZE(__crcu_array),              \
245                         __crcu_array, __rs_array);                      \
246 } while (0)
247 
248 #define wait_rcu_gp(...) _wait_rcu_gp(false, __VA_ARGS__)
249 
250 /**
251  * synchronize_rcu_mult - Wait concurrently for multiple grace periods
252  * @...: List of call_rcu() functions for the flavors to wait on.
253  *
254  * This macro waits concurrently for multiple flavors of RCU grace periods.
255  * For example, synchronize_rcu_mult(call_rcu, call_rcu_bh) would wait
256  * on concurrent RCU and RCU-bh grace periods.  Waiting on a give SRCU
257  * domain requires you to write a wrapper function for that SRCU domain's
258  * call_srcu() function, supplying the corresponding srcu_struct.
259  *
260  * If Tiny RCU, tell _wait_rcu_gp() not to bother waiting for RCU
261  * or RCU-bh, given that anywhere synchronize_rcu_mult() can be called
262  * is automatically a grace period.
263  */
264 #define synchronize_rcu_mult(...) \
265         _wait_rcu_gp(IS_ENABLED(CONFIG_TINY_RCU), __VA_ARGS__)
266 
267 /**
268  * call_rcu_tasks() - Queue an RCU for invocation task-based grace period
269  * @head: structure to be used for queueing the RCU updates.
270  * @func: actual callback function to be invoked after the grace period
271  *
272  * The callback function will be invoked some time after a full grace
273  * period elapses, in other words after all currently executing RCU
274  * read-side critical sections have completed. call_rcu_tasks() assumes
275  * that the read-side critical sections end at a voluntary context
276  * switch (not a preemption!), entry into idle, or transition to usermode
277  * execution.  As such, there are no read-side primitives analogous to
278  * rcu_read_lock() and rcu_read_unlock() because this primitive is intended
279  * to determine that all tasks have passed through a safe state, not so
280  * much for data-strcuture synchronization.
281  *
282  * See the description of call_rcu() for more detailed information on
283  * memory ordering guarantees.
284  */
285 void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
286 void synchronize_rcu_tasks(void);
287 void rcu_barrier_tasks(void);
288 
289 #ifdef CONFIG_PREEMPT_RCU
290 
291 void __rcu_read_lock(void);
292 void __rcu_read_unlock(void);
293 void rcu_read_unlock_special(struct task_struct *t);
294 void synchronize_rcu(void);
295 
296 /*
297  * Defined as a macro as it is a very low level header included from
298  * areas that don't even know about current.  This gives the rcu_read_lock()
299  * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
300  * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
301  */
302 #define rcu_preempt_depth() (current->rcu_read_lock_nesting)
303 
304 #else /* #ifdef CONFIG_PREEMPT_RCU */
305 
306 static inline void __rcu_read_lock(void)
307 {
308         if (IS_ENABLED(CONFIG_PREEMPT_COUNT))
309                 preempt_disable();
310 }
311 
312 static inline void __rcu_read_unlock(void)
313 {
314         if (IS_ENABLED(CONFIG_PREEMPT_COUNT))
315                 preempt_enable();
316 }
317 
318 static inline void synchronize_rcu(void)
319 {
320         synchronize_sched();
321 }
322 
323 static inline int rcu_preempt_depth(void)
324 {
325         return 0;
326 }
327 
328 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
329 
330 /* Internal to kernel */
331 void rcu_init(void);
332 void rcu_sched_qs(void);
333 void rcu_bh_qs(void);
334 void rcu_check_callbacks(int user);
335 struct notifier_block;
336 int rcu_cpu_notify(struct notifier_block *self,
337                    unsigned long action, void *hcpu);
338 
339 #ifndef CONFIG_TINY_RCU
340 void rcu_end_inkernel_boot(void);
341 #else /* #ifndef CONFIG_TINY_RCU */
342 static inline void rcu_end_inkernel_boot(void) { }
343 #endif /* #ifndef CONFIG_TINY_RCU */
344 
345 #ifdef CONFIG_RCU_STALL_COMMON
346 void rcu_sysrq_start(void);
347 void rcu_sysrq_end(void);
348 #else /* #ifdef CONFIG_RCU_STALL_COMMON */
349 static inline void rcu_sysrq_start(void)
350 {
351 }
352 static inline void rcu_sysrq_end(void)
353 {
354 }
355 #endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
356 
357 #ifdef CONFIG_NO_HZ_FULL
358 void rcu_user_enter(void);
359 void rcu_user_exit(void);
360 #else
361 static inline void rcu_user_enter(void) { }
362 static inline void rcu_user_exit(void) { }
363 static inline void rcu_user_hooks_switch(struct task_struct *prev,
364                                          struct task_struct *next) { }
365 #endif /* CONFIG_NO_HZ_FULL */
366 
367 #ifdef CONFIG_RCU_NOCB_CPU
368 void rcu_init_nohz(void);
369 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
370 static inline void rcu_init_nohz(void)
371 {
372 }
373 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
374 
375 /**
376  * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
377  * @a: Code that RCU needs to pay attention to.
378  *
379  * RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden
380  * in the inner idle loop, that is, between the rcu_idle_enter() and
381  * the rcu_idle_exit() -- RCU will happily ignore any such read-side
382  * critical sections.  However, things like powertop need tracepoints
383  * in the inner idle loop.
384  *
385  * This macro provides the way out:  RCU_NONIDLE(do_something_with_RCU())
386  * will tell RCU that it needs to pay attending, invoke its argument
387  * (in this example, a call to the do_something_with_RCU() function),
388  * and then tell RCU to go back to ignoring this CPU.  It is permissible
389  * to nest RCU_NONIDLE() wrappers, but the nesting level is currently
390  * quite limited.  If deeper nesting is required, it will be necessary
391  * to adjust DYNTICK_TASK_NESTING_VALUE accordingly.
392  */
393 #define RCU_NONIDLE(a) \
394         do { \
395                 rcu_irq_enter_irqson(); \
396                 do { a; } while (0); \
397                 rcu_irq_exit_irqson(); \
398         } while (0)
399 
400 /*
401  * Note a voluntary context switch for RCU-tasks benefit.  This is a
402  * macro rather than an inline function to avoid #include hell.
403  */
404 #ifdef CONFIG_TASKS_RCU
405 #define TASKS_RCU(x) x
406 extern struct srcu_struct tasks_rcu_exit_srcu;
407 #define rcu_note_voluntary_context_switch(t) \
408         do { \
409                 rcu_all_qs(); \
410                 if (READ_ONCE((t)->rcu_tasks_holdout)) \
411                         WRITE_ONCE((t)->rcu_tasks_holdout, false); \
412         } while (0)
413 #else /* #ifdef CONFIG_TASKS_RCU */
414 #define TASKS_RCU(x) do { } while (0)
415 #define rcu_note_voluntary_context_switch(t)    rcu_all_qs()
416 #endif /* #else #ifdef CONFIG_TASKS_RCU */
417 
418 /**
419  * cond_resched_rcu_qs - Report potential quiescent states to RCU
420  *
421  * This macro resembles cond_resched(), except that it is defined to
422  * report potential quiescent states to RCU-tasks even if the cond_resched()
423  * machinery were to be shut off, as some advocate for PREEMPT kernels.
424  */
425 #define cond_resched_rcu_qs() \
426 do { \
427         if (!cond_resched()) \
428                 rcu_note_voluntary_context_switch(current); \
429 } while (0)
430 
431 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP)
432 bool __rcu_is_watching(void);
433 #endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP) */
434 
435 /*
436  * Infrastructure to implement the synchronize_() primitives in
437  * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
438  */
439 
440 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
441 #include <linux/rcutree.h>
442 #elif defined(CONFIG_TINY_RCU)
443 #include <linux/rcutiny.h>
444 #else
445 #error "Unknown RCU implementation specified to kernel configuration"
446 #endif
447 
448 /*
449  * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic
450  * initialization and destruction of rcu_head on the stack. rcu_head structures
451  * allocated dynamically in the heap or defined statically don't need any
452  * initialization.
453  */
454 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
455 void init_rcu_head(struct rcu_head *head);
456 void destroy_rcu_head(struct rcu_head *head);
457 void init_rcu_head_on_stack(struct rcu_head *head);
458 void destroy_rcu_head_on_stack(struct rcu_head *head);
459 #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
460 static inline void init_rcu_head(struct rcu_head *head)
461 {
462 }
463 
464 static inline void destroy_rcu_head(struct rcu_head *head)
465 {
466 }
467 
468 static inline void init_rcu_head_on_stack(struct rcu_head *head)
469 {
470 }
471 
472 static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
473 {
474 }
475 #endif  /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
476 
477 #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
478 bool rcu_lockdep_current_cpu_online(void);
479 #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
480 static inline bool rcu_lockdep_current_cpu_online(void)
481 {
482         return true;
483 }
484 #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
485 
486 #ifdef CONFIG_DEBUG_LOCK_ALLOC
487 
488 static inline void rcu_lock_acquire(struct lockdep_map *map)
489 {
490         lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
491 }
492 
493 static inline void rcu_lock_release(struct lockdep_map *map)
494 {
495         lock_release(map, 1, _THIS_IP_);
496 }
497 
498 extern struct lockdep_map rcu_lock_map;
499 extern struct lockdep_map rcu_bh_lock_map;
500 extern struct lockdep_map rcu_sched_lock_map;
501 extern struct lockdep_map rcu_callback_map;
502 int debug_lockdep_rcu_enabled(void);
503 
504 int rcu_read_lock_held(void);
505 int rcu_read_lock_bh_held(void);
506 
507 /**
508  * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
509  *
510  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
511  * RCU-sched read-side critical section.  In absence of
512  * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
513  * critical section unless it can prove otherwise.
514  */
515 #ifdef CONFIG_PREEMPT_COUNT
516 int rcu_read_lock_sched_held(void);
517 #else /* #ifdef CONFIG_PREEMPT_COUNT */
518 static inline int rcu_read_lock_sched_held(void)
519 {
520         return 1;
521 }
522 #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
523 
524 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
525 
526 # define rcu_lock_acquire(a)            do { } while (0)
527 # define rcu_lock_release(a)            do { } while (0)
528 
529 static inline int rcu_read_lock_held(void)
530 {
531         return 1;
532 }
533 
534 static inline int rcu_read_lock_bh_held(void)
535 {
536         return 1;
537 }
538 
539 #ifdef CONFIG_PREEMPT_COUNT
540 static inline int rcu_read_lock_sched_held(void)
541 {
542         return preempt_count() != 0 || irqs_disabled();
543 }
544 #else /* #ifdef CONFIG_PREEMPT_COUNT */
545 static inline int rcu_read_lock_sched_held(void)
546 {
547         return 1;
548 }
549 #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
550 
551 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
552 
553 #ifdef CONFIG_PROVE_RCU
554 
555 /**
556  * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met
557  * @c: condition to check
558  * @s: informative message
559  */
560 #define RCU_LOCKDEP_WARN(c, s)                                          \
561         do {                                                            \
562                 static bool __section(.data.unlikely) __warned;         \
563                 if (debug_lockdep_rcu_enabled() && !__warned && (c)) {  \
564                         __warned = true;                                \
565                         lockdep_rcu_suspicious(__FILE__, __LINE__, s);  \
566                 }                                                       \
567         } while (0)
568 
569 #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
570 static inline void rcu_preempt_sleep_check(void)
571 {
572         RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
573                          "Illegal context switch in RCU read-side critical section");
574 }
575 #else /* #ifdef CONFIG_PROVE_RCU */
576 static inline void rcu_preempt_sleep_check(void)
577 {
578 }
579 #endif /* #else #ifdef CONFIG_PROVE_RCU */
580 
581 #define rcu_sleep_check()                                               \
582         do {                                                            \
583                 rcu_preempt_sleep_check();                              \
584                 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map),        \
585                                  "Illegal context switch in RCU-bh read-side critical section"); \
586                 RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map),     \
587                                  "Illegal context switch in RCU-sched read-side critical section"); \
588         } while (0)
589 
590 #else /* #ifdef CONFIG_PROVE_RCU */
591 
592 #define RCU_LOCKDEP_WARN(c, s) do { } while (0)
593 #define rcu_sleep_check() do { } while (0)
594 
595 #endif /* #else #ifdef CONFIG_PROVE_RCU */
596 
597 /*
598  * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
599  * and rcu_assign_pointer().  Some of these could be folded into their
600  * callers, but they are left separate in order to ease introduction of
601  * multiple flavors of pointers to match the multiple flavors of RCU
602  * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in
603  * the future.
604  */
605 
606 #ifdef __CHECKER__
607 #define rcu_dereference_sparse(p, space) \
608         ((void)(((typeof(*p) space *)p) == p))
609 #else /* #ifdef __CHECKER__ */
610 #define rcu_dereference_sparse(p, space)
611 #endif /* #else #ifdef __CHECKER__ */
612 
613 #define __rcu_access_pointer(p, space) \
614 ({ \
615         typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \
616         rcu_dereference_sparse(p, space); \
617         ((typeof(*p) __force __kernel *)(_________p1)); \
618 })
619 #define __rcu_dereference_check(p, c, space) \
620 ({ \
621         /* Dependency order vs. p above. */ \
622         typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \
623         RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
624         rcu_dereference_sparse(p, space); \
625         ((typeof(*p) __force __kernel *)(________p1)); \
626 })
627 #define __rcu_dereference_protected(p, c, space) \
628 ({ \
629         RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
630         rcu_dereference_sparse(p, space); \
631         ((typeof(*p) __force __kernel *)(p)); \
632 })
633 
634 /**
635  * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
636  * @v: The value to statically initialize with.
637  */
638 #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
639 
640 /**
641  * rcu_assign_pointer() - assign to RCU-protected pointer
642  * @p: pointer to assign to
643  * @v: value to assign (publish)
644  *
645  * Assigns the specified value to the specified RCU-protected
646  * pointer, ensuring that any concurrent RCU readers will see
647  * any prior initialization.
648  *
649  * Inserts memory barriers on architectures that require them
650  * (which is most of them), and also prevents the compiler from
651  * reordering the code that initializes the structure after the pointer
652  * assignment.  More importantly, this call documents which pointers
653  * will be dereferenced by RCU read-side code.
654  *
655  * In some special cases, you may use RCU_INIT_POINTER() instead
656  * of rcu_assign_pointer().  RCU_INIT_POINTER() is a bit faster due
657  * to the fact that it does not constrain either the CPU or the compiler.
658  * That said, using RCU_INIT_POINTER() when you should have used
659  * rcu_assign_pointer() is a very bad thing that results in
660  * impossible-to-diagnose memory corruption.  So please be careful.
661  * See the RCU_INIT_POINTER() comment header for details.
662  *
663  * Note that rcu_assign_pointer() evaluates each of its arguments only
664  * once, appearances notwithstanding.  One of the "extra" evaluations
665  * is in typeof() and the other visible only to sparse (__CHECKER__),
666  * neither of which actually execute the argument.  As with most cpp
667  * macros, this execute-arguments-only-once property is important, so
668  * please be careful when making changes to rcu_assign_pointer() and the
669  * other macros that it invokes.
670  */
671 #define rcu_assign_pointer(p, v) smp_store_release(&p, RCU_INITIALIZER(v))
672 
673 /**
674  * rcu_access_pointer() - fetch RCU pointer with no dereferencing
675  * @p: The pointer to read
676  *
677  * Return the value of the specified RCU-protected pointer, but omit the
678  * smp_read_barrier_depends() and keep the READ_ONCE().  This is useful
679  * when the value of this pointer is accessed, but the pointer is not
680  * dereferenced, for example, when testing an RCU-protected pointer against
681  * NULL.  Although rcu_access_pointer() may also be used in cases where
682  * update-side locks prevent the value of the pointer from changing, you
683  * should instead use rcu_dereference_protected() for this use case.
684  *
685  * It is also permissible to use rcu_access_pointer() when read-side
686  * access to the pointer was removed at least one grace period ago, as
687  * is the case in the context of the RCU callback that is freeing up
688  * the data, or after a synchronize_rcu() returns.  This can be useful
689  * when tearing down multi-linked structures after a grace period
690  * has elapsed.
691  */
692 #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
693 
694 /**
695  * rcu_dereference_check() - rcu_dereference with debug checking
696  * @p: The pointer to read, prior to dereferencing
697  * @c: The conditions under which the dereference will take place
698  *
699  * Do an rcu_dereference(), but check that the conditions under which the
700  * dereference will take place are correct.  Typically the conditions
701  * indicate the various locking conditions that should be held at that
702  * point.  The check should return true if the conditions are satisfied.
703  * An implicit check for being in an RCU read-side critical section
704  * (rcu_read_lock()) is included.
705  *
706  * For example:
707  *
708  *      bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
709  *
710  * could be used to indicate to lockdep that foo->bar may only be dereferenced
711  * if either rcu_read_lock() is held, or that the lock required to replace
712  * the bar struct at foo->bar is held.
713  *
714  * Note that the list of conditions may also include indications of when a lock
715  * need not be held, for example during initialisation or destruction of the
716  * target struct:
717  *
718  *      bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
719  *                                            atomic_read(&foo->usage) == 0);
720  *
721  * Inserts memory barriers on architectures that require them
722  * (currently only the Alpha), prevents the compiler from refetching
723  * (and from merging fetches), and, more importantly, documents exactly
724  * which pointers are protected by RCU and checks that the pointer is
725  * annotated as __rcu.
726  */
727 #define rcu_dereference_check(p, c) \
728         __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
729 
730 /**
731  * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
732  * @p: The pointer to read, prior to dereferencing
733  * @c: The conditions under which the dereference will take place
734  *
735  * This is the RCU-bh counterpart to rcu_dereference_check().
736  */
737 #define rcu_dereference_bh_check(p, c) \
738         __rcu_dereference_check((p), (c) || rcu_read_lock_bh_held(), __rcu)
739 
740 /**
741  * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
742  * @p: The pointer to read, prior to dereferencing
743  * @c: The conditions under which the dereference will take place
744  *
745  * This is the RCU-sched counterpart to rcu_dereference_check().
746  */
747 #define rcu_dereference_sched_check(p, c) \
748         __rcu_dereference_check((p), (c) || rcu_read_lock_sched_held(), \
749                                 __rcu)
750 
751 #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/
752 
753 /*
754  * The tracing infrastructure traces RCU (we want that), but unfortunately
755  * some of the RCU checks causes tracing to lock up the system.
756  *
757  * The no-tracing version of rcu_dereference_raw() must not call
758  * rcu_read_lock_held().
759  */
760 #define rcu_dereference_raw_notrace(p) __rcu_dereference_check((p), 1, __rcu)
761 
762 /**
763  * rcu_dereference_protected() - fetch RCU pointer when updates prevented
764  * @p: The pointer to read, prior to dereferencing
765  * @c: The conditions under which the dereference will take place
766  *
767  * Return the value of the specified RCU-protected pointer, but omit
768  * both the smp_read_barrier_depends() and the READ_ONCE().  This
769  * is useful in cases where update-side locks prevent the value of the
770  * pointer from changing.  Please note that this primitive does -not-
771  * prevent the compiler from repeating this reference or combining it
772  * with other references, so it should not be used without protection
773  * of appropriate locks.
774  *
775  * This function is only for update-side use.  Using this function
776  * when protected only by rcu_read_lock() will result in infrequent
777  * but very ugly failures.
778  */
779 #define rcu_dereference_protected(p, c) \
780         __rcu_dereference_protected((p), (c), __rcu)
781 
782 
783 /**
784  * rcu_dereference() - fetch RCU-protected pointer for dereferencing
785  * @p: The pointer to read, prior to dereferencing
786  *
787  * This is a simple wrapper around rcu_dereference_check().
788  */
789 #define rcu_dereference(p) rcu_dereference_check(p, 0)
790 
791 /**
792  * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
793  * @p: The pointer to read, prior to dereferencing
794  *
795  * Makes rcu_dereference_check() do the dirty work.
796  */
797 #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
798 
799 /**
800  * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
801  * @p: The pointer to read, prior to dereferencing
802  *
803  * Makes rcu_dereference_check() do the dirty work.
804  */
805 #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
806 
807 /**
808  * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism
809  * @p: The pointer to hand off
810  *
811  * This is simply an identity function, but it documents where a pointer
812  * is handed off from RCU to some other synchronization mechanism, for
813  * example, reference counting or locking.  In C11, it would map to
814  * kill_dependency().  It could be used as follows:
815  *
816  *      rcu_read_lock();
817  *      p = rcu_dereference(gp);
818  *      long_lived = is_long_lived(p);
819  *      if (long_lived) {
820  *              if (!atomic_inc_not_zero(p->refcnt))
821  *                      long_lived = false;
822  *              else
823  *                      p = rcu_pointer_handoff(p);
824  *      }
825  *      rcu_read_unlock();
826  */
827 #define rcu_pointer_handoff(p) (p)
828 
829 /**
830  * rcu_read_lock() - mark the beginning of an RCU read-side critical section
831  *
832  * When synchronize_rcu() is invoked on one CPU while other CPUs
833  * are within RCU read-side critical sections, then the
834  * synchronize_rcu() is guaranteed to block until after all the other
835  * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
836  * on one CPU while other CPUs are within RCU read-side critical
837  * sections, invocation of the corresponding RCU callback is deferred
838  * until after the all the other CPUs exit their critical sections.
839  *
840  * Note, however, that RCU callbacks are permitted to run concurrently
841  * with new RCU read-side critical sections.  One way that this can happen
842  * is via the following sequence of events: (1) CPU 0 enters an RCU
843  * read-side critical section, (2) CPU 1 invokes call_rcu() to register
844  * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
845  * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
846  * callback is invoked.  This is legal, because the RCU read-side critical
847  * section that was running concurrently with the call_rcu() (and which
848  * therefore might be referencing something that the corresponding RCU
849  * callback would free up) has completed before the corresponding
850  * RCU callback is invoked.
851  *
852  * RCU read-side critical sections may be nested.  Any deferred actions
853  * will be deferred until the outermost RCU read-side critical section
854  * completes.
855  *
856  * You can avoid reading and understanding the next paragraph by
857  * following this rule: don't put anything in an rcu_read_lock() RCU
858  * read-side critical section that would block in a !PREEMPT kernel.
859  * But if you want the full story, read on!
860  *
861  * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU),
862  * it is illegal to block while in an RCU read-side critical section.
863  * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPT
864  * kernel builds, RCU read-side critical sections may be preempted,
865  * but explicit blocking is illegal.  Finally, in preemptible RCU
866  * implementations in real-time (with -rt patchset) kernel builds, RCU
867  * read-side critical sections may be preempted and they may also block, but
868  * only when acquiring spinlocks that are subject to priority inheritance.
869  */
870 static inline void rcu_read_lock(void)
871 {
872         __rcu_read_lock();
873         __acquire(RCU);
874         rcu_lock_acquire(&rcu_lock_map);
875         RCU_LOCKDEP_WARN(!rcu_is_watching(),
876                          "rcu_read_lock() used illegally while idle");
877 }
878 
879 /*
880  * So where is rcu_write_lock()?  It does not exist, as there is no
881  * way for writers to lock out RCU readers.  This is a feature, not
882  * a bug -- this property is what provides RCU's performance benefits.
883  * Of course, writers must coordinate with each other.  The normal
884  * spinlock primitives work well for this, but any other technique may be
885  * used as well.  RCU does not care how the writers keep out of each
886  * others' way, as long as they do so.
887  */
888 
889 /**
890  * rcu_read_unlock() - marks the end of an RCU read-side critical section.
891  *
892  * In most situations, rcu_read_unlock() is immune from deadlock.
893  * However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock()
894  * is responsible for deboosting, which it does via rt_mutex_unlock().
895  * Unfortunately, this function acquires the scheduler's runqueue and
896  * priority-inheritance spinlocks.  This means that deadlock could result
897  * if the caller of rcu_read_unlock() already holds one of these locks or
898  * any lock that is ever acquired while holding them; or any lock which
899  * can be taken from interrupt context because rcu_boost()->rt_mutex_lock()
900  * does not disable irqs while taking ->wait_lock.
901  *
902  * That said, RCU readers are never priority boosted unless they were
903  * preempted.  Therefore, one way to avoid deadlock is to make sure
904  * that preemption never happens within any RCU read-side critical
905  * section whose outermost rcu_read_unlock() is called with one of
906  * rt_mutex_unlock()'s locks held.  Such preemption can be avoided in
907  * a number of ways, for example, by invoking preempt_disable() before
908  * critical section's outermost rcu_read_lock().
909  *
910  * Given that the set of locks acquired by rt_mutex_unlock() might change
911  * at any time, a somewhat more future-proofed approach is to make sure
912  * that that preemption never happens within any RCU read-side critical
913  * section whose outermost rcu_read_unlock() is called with irqs disabled.
914  * This approach relies on the fact that rt_mutex_unlock() currently only
915  * acquires irq-disabled locks.
916  *
917  * The second of these two approaches is best in most situations,
918  * however, the first approach can also be useful, at least to those
919  * developers willing to keep abreast of the set of locks acquired by
920  * rt_mutex_unlock().
921  *
922  * See rcu_read_lock() for more information.
923  */
924 static inline void rcu_read_unlock(void)
925 {
926         RCU_LOCKDEP_WARN(!rcu_is_watching(),
927                          "rcu_read_unlock() used illegally while idle");
928         __release(RCU);
929         __rcu_read_unlock();
930         rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
931 }
932 
933 /**
934  * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
935  *
936  * This is equivalent of rcu_read_lock(), but to be used when updates
937  * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since
938  * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a
939  * softirq handler to be a quiescent state, a process in RCU read-side
940  * critical section must be protected by disabling softirqs. Read-side
941  * critical sections in interrupt context can use just rcu_read_lock(),
942  * though this should at least be commented to avoid confusing people
943  * reading the code.
944  *
945  * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
946  * must occur in the same context, for example, it is illegal to invoke
947  * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
948  * was invoked from some other task.
949  */
950 static inline void rcu_read_lock_bh(void)
951 {
952         local_bh_disable();
953         __acquire(RCU_BH);
954         rcu_lock_acquire(&rcu_bh_lock_map);
955         RCU_LOCKDEP_WARN(!rcu_is_watching(),
956                          "rcu_read_lock_bh() used illegally while idle");
957 }
958 
959 /*
960  * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
961  *
962  * See rcu_read_lock_bh() for more information.
963  */
964 static inline void rcu_read_unlock_bh(void)
965 {
966         RCU_LOCKDEP_WARN(!rcu_is_watching(),
967                          "rcu_read_unlock_bh() used illegally while idle");
968         rcu_lock_release(&rcu_bh_lock_map);
969         __release(RCU_BH);
970         local_bh_enable();
971 }
972 
973 /**
974  * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
975  *
976  * This is equivalent of rcu_read_lock(), but to be used when updates
977  * are being done using call_rcu_sched() or synchronize_rcu_sched().
978  * Read-side critical sections can also be introduced by anything that
979  * disables preemption, including local_irq_disable() and friends.
980  *
981  * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
982  * must occur in the same context, for example, it is illegal to invoke
983  * rcu_read_unlock_sched() from process context if the matching
984  * rcu_read_lock_sched() was invoked from an NMI handler.
985  */
986 static inline void rcu_read_lock_sched(void)
987 {
988         preempt_disable();
989         __acquire(RCU_SCHED);
990         rcu_lock_acquire(&rcu_sched_lock_map);
991         RCU_LOCKDEP_WARN(!rcu_is_watching(),
992                          "rcu_read_lock_sched() used illegally while idle");
993 }
994 
995 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
996 static inline notrace void rcu_read_lock_sched_notrace(void)
997 {
998         preempt_disable_notrace();
999         __acquire(RCU_SCHED);
1000 }
1001 
1002 /*
1003  * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
1004  *
1005  * See rcu_read_lock_sched for more information.
1006  */
1007 static inline void rcu_read_unlock_sched(void)
1008 {
1009         RCU_LOCKDEP_WARN(!rcu_is_watching(),
1010                          "rcu_read_unlock_sched() used illegally while idle");
1011         rcu_lock_release(&rcu_sched_lock_map);
1012         __release(RCU_SCHED);
1013         preempt_enable();
1014 }
1015 
1016 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
1017 static inline notrace void rcu_read_unlock_sched_notrace(void)
1018 {
1019         __release(RCU_SCHED);
1020         preempt_enable_notrace();
1021 }
1022 
1023 /**
1024  * RCU_INIT_POINTER() - initialize an RCU protected pointer
1025  *
1026  * Initialize an RCU-protected pointer in special cases where readers
1027  * do not need ordering constraints on the CPU or the compiler.  These
1028  * special cases are:
1029  *
1030  * 1.   This use of RCU_INIT_POINTER() is NULLing out the pointer -or-
1031  * 2.   The caller has taken whatever steps are required to prevent
1032  *      RCU readers from concurrently accessing this pointer -or-
1033  * 3.   The referenced data structure has already been exposed to
1034  *      readers either at compile time or via rcu_assign_pointer() -and-
1035  *      a.      You have not made -any- reader-visible changes to
1036  *              this structure since then -or-
1037  *      b.      It is OK for readers accessing this structure from its
1038  *              new location to see the old state of the structure.  (For
1039  *              example, the changes were to statistical counters or to
1040  *              other state where exact synchronization is not required.)
1041  *
1042  * Failure to follow these rules governing use of RCU_INIT_POINTER() will
1043  * result in impossible-to-diagnose memory corruption.  As in the structures
1044  * will look OK in crash dumps, but any concurrent RCU readers might
1045  * see pre-initialized values of the referenced data structure.  So
1046  * please be very careful how you use RCU_INIT_POINTER()!!!
1047  *
1048  * If you are creating an RCU-protected linked structure that is accessed
1049  * by a single external-to-structure RCU-protected pointer, then you may
1050  * use RCU_INIT_POINTER() to initialize the internal RCU-protected
1051  * pointers, but you must use rcu_assign_pointer() to initialize the
1052  * external-to-structure pointer -after- you have completely initialized
1053  * the reader-accessible portions of the linked structure.
1054  *
1055  * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
1056  * ordering guarantees for either the CPU or the compiler.
1057  */
1058 #define RCU_INIT_POINTER(p, v) \
1059         do { \
1060                 rcu_dereference_sparse(p, __rcu); \
1061                 WRITE_ONCE(p, RCU_INITIALIZER(v)); \
1062         } while (0)
1063 
1064 /**
1065  * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
1066  *
1067  * GCC-style initialization for an RCU-protected pointer in a structure field.
1068  */
1069 #define RCU_POINTER_INITIALIZER(p, v) \
1070                 .p = RCU_INITIALIZER(v)
1071 
1072 /*
1073  * Does the specified offset indicate that the corresponding rcu_head
1074  * structure can be handled by kfree_rcu()?
1075  */
1076 #define __is_kfree_rcu_offset(offset) ((offset) < 4096)
1077 
1078 /*
1079  * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain.
1080  */
1081 #define __kfree_rcu(head, offset) \
1082         do { \
1083                 BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \
1084                 kfree_call_rcu(head, (rcu_callback_t)(unsigned long)(offset)); \
1085         } while (0)
1086 
1087 /**
1088  * kfree_rcu() - kfree an object after a grace period.
1089  * @ptr:        pointer to kfree
1090  * @rcu_head:   the name of the struct rcu_head within the type of @ptr.
1091  *
1092  * Many rcu callbacks functions just call kfree() on the base structure.
1093  * These functions are trivial, but their size adds up, and furthermore
1094  * when they are used in a kernel module, that module must invoke the
1095  * high-latency rcu_barrier() function at module-unload time.
1096  *
1097  * The kfree_rcu() function handles this issue.  Rather than encoding a
1098  * function address in the embedded rcu_head structure, kfree_rcu() instead
1099  * encodes the offset of the rcu_head structure within the base structure.
1100  * Because the functions are not allowed in the low-order 4096 bytes of
1101  * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
1102  * If the offset is larger than 4095 bytes, a compile-time error will
1103  * be generated in __kfree_rcu().  If this error is triggered, you can
1104  * either fall back to use of call_rcu() or rearrange the structure to
1105  * position the rcu_head structure into the first 4096 bytes.
1106  *
1107  * Note that the allowable offset might decrease in the future, for example,
1108  * to allow something like kmem_cache_free_rcu().
1109  *
1110  * The BUILD_BUG_ON check must not involve any function calls, hence the
1111  * checks are done in macros here.
1112  */
1113 #define kfree_rcu(ptr, rcu_head)                                        \
1114         __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
1115 
1116 #ifdef CONFIG_TINY_RCU
1117 static inline int rcu_needs_cpu(u64 basemono, u64 *nextevt)
1118 {
1119         *nextevt = KTIME_MAX;
1120         return 0;
1121 }
1122 #endif /* #ifdef CONFIG_TINY_RCU */
1123 
1124 #if defined(CONFIG_RCU_NOCB_CPU_ALL)
1125 static inline bool rcu_is_nocb_cpu(int cpu) { return true; }
1126 #elif defined(CONFIG_RCU_NOCB_CPU)
1127 bool rcu_is_nocb_cpu(int cpu);
1128 #else
1129 static inline bool rcu_is_nocb_cpu(int cpu) { return false; }
1130 #endif
1131 
1132 
1133 /* Only for use by adaptive-ticks code. */
1134 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
1135 bool rcu_sys_is_idle(void);
1136 void rcu_sysidle_force_exit(void);
1137 #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
1138 
1139 static inline bool rcu_sys_is_idle(void)
1140 {
1141         return false;
1142 }
1143 
1144 static inline void rcu_sysidle_force_exit(void)
1145 {
1146 }
1147 
1148 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
1149 
1150 
1151 #endif /* __LINUX_RCUPDATE_H */
1152 

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