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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 #include <linux/irqflags.h>
 49 
 50 #include <asm/barrier.h>
 51 
 52 #ifndef CONFIG_TINY_RCU
 53 extern int rcu_expedited; /* for sysctl */
 54 extern int rcu_normal;    /* also for sysctl */
 55 #endif /* #ifndef CONFIG_TINY_RCU */
 56 
 57 #ifdef CONFIG_TINY_RCU
 58 /* Tiny RCU doesn't expedite, as its purpose in life is instead to be tiny. */
 59 static inline bool rcu_gp_is_normal(void)  /* Internal RCU use. */
 60 {
 61         return true;
 62 }
 63 static inline bool rcu_gp_is_expedited(void)  /* Internal RCU use. */
 64 {
 65         return false;
 66 }
 67 
 68 static inline void rcu_expedite_gp(void)
 69 {
 70 }
 71 
 72 static inline void rcu_unexpedite_gp(void)
 73 {
 74 }
 75 #else /* #ifdef CONFIG_TINY_RCU */
 76 bool rcu_gp_is_normal(void);     /* Internal RCU use. */
 77 bool rcu_gp_is_expedited(void);  /* Internal RCU use. */
 78 void rcu_expedite_gp(void);
 79 void rcu_unexpedite_gp(void);
 80 #endif /* #else #ifdef CONFIG_TINY_RCU */
 81 
 82 enum rcutorture_type {
 83         RCU_FLAVOR,
 84         RCU_BH_FLAVOR,
 85         RCU_SCHED_FLAVOR,
 86         RCU_TASKS_FLAVOR,
 87         SRCU_FLAVOR,
 88         INVALID_RCU_FLAVOR
 89 };
 90 
 91 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
 92 void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
 93                             unsigned long *gpnum, unsigned long *completed);
 94 void rcutorture_record_test_transition(void);
 95 void rcutorture_record_progress(unsigned long vernum);
 96 void do_trace_rcu_torture_read(const char *rcutorturename,
 97                                struct rcu_head *rhp,
 98                                unsigned long secs,
 99                                unsigned long c_old,
100                                unsigned long c);
101 #else
102 static inline void rcutorture_get_gp_data(enum rcutorture_type test_type,
103                                           int *flags,
104                                           unsigned long *gpnum,
105                                           unsigned long *completed)
106 {
107         *flags = 0;
108         *gpnum = 0;
109         *completed = 0;
110 }
111 static inline void rcutorture_record_test_transition(void)
112 {
113 }
114 static inline void rcutorture_record_progress(unsigned long vernum)
115 {
116 }
117 #ifdef CONFIG_RCU_TRACE
118 void do_trace_rcu_torture_read(const char *rcutorturename,
119                                struct rcu_head *rhp,
120                                unsigned long secs,
121                                unsigned long c_old,
122                                unsigned long c);
123 #else
124 #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
125         do { } while (0)
126 #endif
127 #endif
128 
129 #define UINT_CMP_GE(a, b)       (UINT_MAX / 2 >= (a) - (b))
130 #define UINT_CMP_LT(a, b)       (UINT_MAX / 2 < (a) - (b))
131 #define ULONG_CMP_GE(a, b)      (ULONG_MAX / 2 >= (a) - (b))
132 #define ULONG_CMP_LT(a, b)      (ULONG_MAX / 2 < (a) - (b))
133 #define ulong2long(a)           (*(long *)(&(a)))
134 
135 /* Exported common interfaces */
136 
137 #ifdef CONFIG_PREEMPT_RCU
138 
139 /**
140  * call_rcu() - Queue an RCU callback for invocation after a grace period.
141  * @head: structure to be used for queueing the RCU updates.
142  * @func: actual callback function to be invoked after the grace period
143  *
144  * The callback function will be invoked some time after a full grace
145  * period elapses, in other words after all pre-existing RCU read-side
146  * critical sections have completed.  However, the callback function
147  * might well execute concurrently with RCU read-side critical sections
148  * that started after call_rcu() was invoked.  RCU read-side critical
149  * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
150  * and may be nested.
151  *
152  * Note that all CPUs must agree that the grace period extended beyond
153  * all pre-existing RCU read-side critical section.  On systems with more
154  * than one CPU, this means that when "func()" is invoked, each CPU is
155  * guaranteed to have executed a full memory barrier since the end of its
156  * last RCU read-side critical section whose beginning preceded the call
157  * to call_rcu().  It also means that each CPU executing an RCU read-side
158  * critical section that continues beyond the start of "func()" must have
159  * executed a memory barrier after the call_rcu() but before the beginning
160  * of that RCU read-side critical section.  Note that these guarantees
161  * include CPUs that are offline, idle, or executing in user mode, as
162  * well as CPUs that are executing in the kernel.
163  *
164  * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
165  * resulting RCU callback function "func()", then both CPU A and CPU B are
166  * guaranteed to execute a full memory barrier during the time interval
167  * between the call to call_rcu() and the invocation of "func()" -- even
168  * if CPU A and CPU B are the same CPU (but again only if the system has
169  * more than one CPU).
170  */
171 void call_rcu(struct rcu_head *head,
172               rcu_callback_t func);
173 
174 #else /* #ifdef CONFIG_PREEMPT_RCU */
175 
176 /* In classic RCU, call_rcu() is just call_rcu_sched(). */
177 #define call_rcu        call_rcu_sched
178 
179 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
180 
181 /**
182  * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
183  * @head: structure to be used for queueing the RCU updates.
184  * @func: actual callback function to be invoked after the grace period
185  *
186  * The callback function will be invoked some time after a full grace
187  * period elapses, in other words after all currently executing RCU
188  * read-side critical sections have completed. call_rcu_bh() assumes
189  * that the read-side critical sections end on completion of a softirq
190  * handler. This means that read-side critical sections in process
191  * context must not be interrupted by softirqs. This interface is to be
192  * used when most of the read-side critical sections are in softirq context.
193  * RCU read-side critical sections are delimited by :
194  *  - rcu_read_lock() and  rcu_read_unlock(), if in interrupt context.
195  *  OR
196  *  - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
197  *  These may be nested.
198  *
199  * See the description of call_rcu() for more detailed information on
200  * memory ordering guarantees.
201  */
202 void call_rcu_bh(struct rcu_head *head,
203                  rcu_callback_t func);
204 
205 /**
206  * call_rcu_sched() - Queue an RCU for invocation after sched grace period.
207  * @head: structure to be used for queueing the RCU updates.
208  * @func: actual callback function to be invoked after the grace period
209  *
210  * The callback function will be invoked some time after a full grace
211  * period elapses, in other words after all currently executing RCU
212  * read-side critical sections have completed. call_rcu_sched() assumes
213  * that the read-side critical sections end on enabling of preemption
214  * or on voluntary preemption.
215  * RCU read-side critical sections are delimited by :
216  *  - rcu_read_lock_sched() and  rcu_read_unlock_sched(),
217  *  OR
218  *  anything that disables preemption.
219  *  These may be nested.
220  *
221  * See the description of call_rcu() for more detailed information on
222  * memory ordering guarantees.
223  */
224 void call_rcu_sched(struct rcu_head *head,
225                     rcu_callback_t func);
226 
227 void synchronize_sched(void);
228 
229 /*
230  * Structure allowing asynchronous waiting on RCU.
231  */
232 struct rcu_synchronize {
233         struct rcu_head head;
234         struct completion completion;
235 };
236 void wakeme_after_rcu(struct rcu_head *head);
237 
238 void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
239                    struct rcu_synchronize *rs_array);
240 
241 #define _wait_rcu_gp(checktiny, ...) \
242 do {                                                                    \
243         call_rcu_func_t __crcu_array[] = { __VA_ARGS__ };               \
244         struct rcu_synchronize __rs_array[ARRAY_SIZE(__crcu_array)];    \
245         __wait_rcu_gp(checktiny, ARRAY_SIZE(__crcu_array),              \
246                         __crcu_array, __rs_array);                      \
247 } while (0)
248 
249 #define wait_rcu_gp(...) _wait_rcu_gp(false, __VA_ARGS__)
250 
251 /**
252  * synchronize_rcu_mult - Wait concurrently for multiple grace periods
253  * @...: List of call_rcu() functions for the flavors to wait on.
254  *
255  * This macro waits concurrently for multiple flavors of RCU grace periods.
256  * For example, synchronize_rcu_mult(call_rcu, call_rcu_bh) would wait
257  * on concurrent RCU and RCU-bh grace periods.  Waiting on a give SRCU
258  * domain requires you to write a wrapper function for that SRCU domain's
259  * call_srcu() function, supplying the corresponding srcu_struct.
260  *
261  * If Tiny RCU, tell _wait_rcu_gp() not to bother waiting for RCU
262  * or RCU-bh, given that anywhere synchronize_rcu_mult() can be called
263  * is automatically a grace period.
264  */
265 #define synchronize_rcu_mult(...) \
266         _wait_rcu_gp(IS_ENABLED(CONFIG_TINY_RCU), __VA_ARGS__)
267 
268 /**
269  * call_rcu_tasks() - Queue an RCU for invocation task-based grace period
270  * @head: structure to be used for queueing the RCU updates.
271  * @func: actual callback function to be invoked after the grace period
272  *
273  * The callback function will be invoked some time after a full grace
274  * period elapses, in other words after all currently executing RCU
275  * read-side critical sections have completed. call_rcu_tasks() assumes
276  * that the read-side critical sections end at a voluntary context
277  * switch (not a preemption!), entry into idle, or transition to usermode
278  * execution.  As such, there are no read-side primitives analogous to
279  * rcu_read_lock() and rcu_read_unlock() because this primitive is intended
280  * to determine that all tasks have passed through a safe state, not so
281  * much for data-strcuture synchronization.
282  *
283  * See the description of call_rcu() for more detailed information on
284  * memory ordering guarantees.
285  */
286 void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
287 void synchronize_rcu_tasks(void);
288 void rcu_barrier_tasks(void);
289 
290 #ifdef CONFIG_PREEMPT_RCU
291 
292 void __rcu_read_lock(void);
293 void __rcu_read_unlock(void);
294 void rcu_read_unlock_special(struct task_struct *t);
295 void synchronize_rcu(void);
296 
297 /*
298  * Defined as a macro as it is a very low level header included from
299  * areas that don't even know about current.  This gives the rcu_read_lock()
300  * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
301  * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
302  */
303 #define rcu_preempt_depth() (current->rcu_read_lock_nesting)
304 
305 #else /* #ifdef CONFIG_PREEMPT_RCU */
306 
307 static inline void __rcu_read_lock(void)
308 {
309         if (IS_ENABLED(CONFIG_PREEMPT_COUNT))
310                 preempt_disable();
311 }
312 
313 static inline void __rcu_read_unlock(void)
314 {
315         if (IS_ENABLED(CONFIG_PREEMPT_COUNT))
316                 preempt_enable();
317 }
318 
319 static inline void synchronize_rcu(void)
320 {
321         synchronize_sched();
322 }
323 
324 static inline int rcu_preempt_depth(void)
325 {
326         return 0;
327 }
328 
329 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
330 
331 /* Internal to kernel */
332 void rcu_init(void);
333 void rcu_sched_qs(void);
334 void rcu_bh_qs(void);
335 void rcu_check_callbacks(int user);
336 void rcu_report_dead(unsigned int cpu);
337 void rcu_cpu_starting(unsigned int cpu);
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 #endif /* CONFIG_NO_HZ_FULL */
364 
365 #ifdef CONFIG_RCU_NOCB_CPU
366 void rcu_init_nohz(void);
367 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
368 static inline void rcu_init_nohz(void)
369 {
370 }
371 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
372 
373 /**
374  * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
375  * @a: Code that RCU needs to pay attention to.
376  *
377  * RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden
378  * in the inner idle loop, that is, between the rcu_idle_enter() and
379  * the rcu_idle_exit() -- RCU will happily ignore any such read-side
380  * critical sections.  However, things like powertop need tracepoints
381  * in the inner idle loop.
382  *
383  * This macro provides the way out:  RCU_NONIDLE(do_something_with_RCU())
384  * will tell RCU that it needs to pay attention, invoke its argument
385  * (in this example, calling the do_something_with_RCU() function),
386  * and then tell RCU to go back to ignoring this CPU.  It is permissible
387  * to nest RCU_NONIDLE() wrappers, but not indefinitely (but the limit is
388  * on the order of a million or so, even on 32-bit systems).  It is
389  * not legal to block within RCU_NONIDLE(), nor is it permissible to
390  * transfer control either into or out of RCU_NONIDLE()'s statement.
391  */
392 #define RCU_NONIDLE(a) \
393         do { \
394                 rcu_irq_enter_irqson(); \
395                 do { a; } while (0); \
396                 rcu_irq_exit_irqson(); \
397         } while (0)
398 
399 /*
400  * Note a voluntary context switch for RCU-tasks benefit.  This is a
401  * macro rather than an inline function to avoid #include hell.
402  */
403 #ifdef CONFIG_TASKS_RCU
404 #define TASKS_RCU(x) x
405 extern struct srcu_struct tasks_rcu_exit_srcu;
406 #define rcu_note_voluntary_context_switch(t) \
407         do { \
408                 rcu_all_qs(); \
409                 if (READ_ONCE((t)->rcu_tasks_holdout)) \
410                         WRITE_ONCE((t)->rcu_tasks_holdout, false); \
411         } while (0)
412 #else /* #ifdef CONFIG_TASKS_RCU */
413 #define TASKS_RCU(x) do { } while (0)
414 #define rcu_note_voluntary_context_switch(t)    rcu_all_qs()
415 #endif /* #else #ifdef CONFIG_TASKS_RCU */
416 
417 /**
418  * cond_resched_rcu_qs - Report potential quiescent states to RCU
419  *
420  * This macro resembles cond_resched(), except that it is defined to
421  * report potential quiescent states to RCU-tasks even if the cond_resched()
422  * machinery were to be shut off, as some advocate for PREEMPT kernels.
423  */
424 #define cond_resched_rcu_qs() \
425 do { \
426         if (!cond_resched()) \
427                 rcu_note_voluntary_context_switch(current); \
428 } while (0)
429 
430 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP)
431 bool __rcu_is_watching(void);
432 #endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP) */
433 
434 /*
435  * Infrastructure to implement the synchronize_() primitives in
436  * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
437  */
438 
439 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
440 #include <linux/rcutree.h>
441 #elif defined(CONFIG_TINY_RCU)
442 #include <linux/rcutiny.h>
443 #else
444 #error "Unknown RCU implementation specified to kernel configuration"
445 #endif
446 
447 #define RCU_SCHEDULER_INACTIVE  0
448 #define RCU_SCHEDULER_INIT      1
449 #define RCU_SCHEDULER_RUNNING   2
450 
451 /*
452  * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic
453  * initialization and destruction of rcu_head on the stack. rcu_head structures
454  * allocated dynamically in the heap or defined statically don't need any
455  * initialization.
456  */
457 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
458 void init_rcu_head(struct rcu_head *head);
459 void destroy_rcu_head(struct rcu_head *head);
460 void init_rcu_head_on_stack(struct rcu_head *head);
461 void destroy_rcu_head_on_stack(struct rcu_head *head);
462 #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
463 static inline void init_rcu_head(struct rcu_head *head)
464 {
465 }
466 
467 static inline void destroy_rcu_head(struct rcu_head *head)
468 {
469 }
470 
471 static inline void init_rcu_head_on_stack(struct rcu_head *head)
472 {
473 }
474 
475 static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
476 {
477 }
478 #endif  /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
479 
480 #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
481 bool rcu_lockdep_current_cpu_online(void);
482 #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
483 static inline bool rcu_lockdep_current_cpu_online(void)
484 {
485         return true;
486 }
487 #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
488 
489 #ifdef CONFIG_DEBUG_LOCK_ALLOC
490 
491 static inline void rcu_lock_acquire(struct lockdep_map *map)
492 {
493         lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
494 }
495 
496 static inline void rcu_lock_release(struct lockdep_map *map)
497 {
498         lock_release(map, 1, _THIS_IP_);
499 }
500 
501 extern struct lockdep_map rcu_lock_map;
502 extern struct lockdep_map rcu_bh_lock_map;
503 extern struct lockdep_map rcu_sched_lock_map;
504 extern struct lockdep_map rcu_callback_map;
505 int debug_lockdep_rcu_enabled(void);
506 
507 int rcu_read_lock_held(void);
508 int rcu_read_lock_bh_held(void);
509 
510 /**
511  * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
512  *
513  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
514  * RCU-sched read-side critical section.  In absence of
515  * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
516  * critical section unless it can prove otherwise.
517  */
518 int rcu_read_lock_sched_held(void);
519 
520 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
521 
522 # define rcu_lock_acquire(a)            do { } while (0)
523 # define rcu_lock_release(a)            do { } while (0)
524 
525 static inline int rcu_read_lock_held(void)
526 {
527         return 1;
528 }
529 
530 static inline int rcu_read_lock_bh_held(void)
531 {
532         return 1;
533 }
534 
535 static inline int rcu_read_lock_sched_held(void)
536 {
537         return !preemptible();
538 }
539 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
540 
541 #ifdef CONFIG_PROVE_RCU
542 
543 /**
544  * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met
545  * @c: condition to check
546  * @s: informative message
547  */
548 #define RCU_LOCKDEP_WARN(c, s)                                          \
549         do {                                                            \
550                 static bool __section(.data.unlikely) __warned;         \
551                 if (debug_lockdep_rcu_enabled() && !__warned && (c)) {  \
552                         __warned = true;                                \
553                         lockdep_rcu_suspicious(__FILE__, __LINE__, s);  \
554                 }                                                       \
555         } while (0)
556 
557 #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
558 static inline void rcu_preempt_sleep_check(void)
559 {
560         RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
561                          "Illegal context switch in RCU read-side critical section");
562 }
563 #else /* #ifdef CONFIG_PROVE_RCU */
564 static inline void rcu_preempt_sleep_check(void)
565 {
566 }
567 #endif /* #else #ifdef CONFIG_PROVE_RCU */
568 
569 #define rcu_sleep_check()                                               \
570         do {                                                            \
571                 rcu_preempt_sleep_check();                              \
572                 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map),        \
573                                  "Illegal context switch in RCU-bh read-side critical section"); \
574                 RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map),     \
575                                  "Illegal context switch in RCU-sched read-side critical section"); \
576         } while (0)
577 
578 #else /* #ifdef CONFIG_PROVE_RCU */
579 
580 #define RCU_LOCKDEP_WARN(c, s) do { } while (0)
581 #define rcu_sleep_check() do { } while (0)
582 
583 #endif /* #else #ifdef CONFIG_PROVE_RCU */
584 
585 /*
586  * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
587  * and rcu_assign_pointer().  Some of these could be folded into their
588  * callers, but they are left separate in order to ease introduction of
589  * multiple flavors of pointers to match the multiple flavors of RCU
590  * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in
591  * the future.
592  */
593 
594 #ifdef __CHECKER__
595 #define rcu_dereference_sparse(p, space) \
596         ((void)(((typeof(*p) space *)p) == p))
597 #else /* #ifdef __CHECKER__ */
598 #define rcu_dereference_sparse(p, space)
599 #endif /* #else #ifdef __CHECKER__ */
600 
601 #define __rcu_access_pointer(p, space) \
602 ({ \
603         typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \
604         rcu_dereference_sparse(p, space); \
605         ((typeof(*p) __force __kernel *)(_________p1)); \
606 })
607 #define __rcu_dereference_check(p, c, space) \
608 ({ \
609         /* Dependency order vs. p above. */ \
610         typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \
611         RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
612         rcu_dereference_sparse(p, space); \
613         ((typeof(*p) __force __kernel *)(________p1)); \
614 })
615 #define __rcu_dereference_protected(p, c, space) \
616 ({ \
617         RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
618         rcu_dereference_sparse(p, space); \
619         ((typeof(*p) __force __kernel *)(p)); \
620 })
621 #define rcu_dereference_raw(p) \
622 ({ \
623         /* Dependency order vs. p above. */ \
624         typeof(p) ________p1 = lockless_dereference(p); \
625         ((typeof(*p) __force __kernel *)(________p1)); \
626 })
627 
628 /**
629  * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
630  * @v: The value to statically initialize with.
631  */
632 #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
633 
634 /**
635  * rcu_assign_pointer() - assign to RCU-protected pointer
636  * @p: pointer to assign to
637  * @v: value to assign (publish)
638  *
639  * Assigns the specified value to the specified RCU-protected
640  * pointer, ensuring that any concurrent RCU readers will see
641  * any prior initialization.
642  *
643  * Inserts memory barriers on architectures that require them
644  * (which is most of them), and also prevents the compiler from
645  * reordering the code that initializes the structure after the pointer
646  * assignment.  More importantly, this call documents which pointers
647  * will be dereferenced by RCU read-side code.
648  *
649  * In some special cases, you may use RCU_INIT_POINTER() instead
650  * of rcu_assign_pointer().  RCU_INIT_POINTER() is a bit faster due
651  * to the fact that it does not constrain either the CPU or the compiler.
652  * That said, using RCU_INIT_POINTER() when you should have used
653  * rcu_assign_pointer() is a very bad thing that results in
654  * impossible-to-diagnose memory corruption.  So please be careful.
655  * See the RCU_INIT_POINTER() comment header for details.
656  *
657  * Note that rcu_assign_pointer() evaluates each of its arguments only
658  * once, appearances notwithstanding.  One of the "extra" evaluations
659  * is in typeof() and the other visible only to sparse (__CHECKER__),
660  * neither of which actually execute the argument.  As with most cpp
661  * macros, this execute-arguments-only-once property is important, so
662  * please be careful when making changes to rcu_assign_pointer() and the
663  * other macros that it invokes.
664  */
665 #define rcu_assign_pointer(p, v)                                              \
666 ({                                                                            \
667         uintptr_t _r_a_p__v = (uintptr_t)(v);                                 \
668                                                                               \
669         if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL)        \
670                 WRITE_ONCE((p), (typeof(p))(_r_a_p__v));                      \
671         else                                                                  \
672                 smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \
673         _r_a_p__v;                                                            \
674 })
675 
676 /**
677  * rcu_access_pointer() - fetch RCU pointer with no dereferencing
678  * @p: The pointer to read
679  *
680  * Return the value of the specified RCU-protected pointer, but omit the
681  * smp_read_barrier_depends() and keep the READ_ONCE().  This is useful
682  * when the value of this pointer is accessed, but the pointer is not
683  * dereferenced, for example, when testing an RCU-protected pointer against
684  * NULL.  Although rcu_access_pointer() may also be used in cases where
685  * update-side locks prevent the value of the pointer from changing, you
686  * should instead use rcu_dereference_protected() for this use case.
687  *
688  * It is also permissible to use rcu_access_pointer() when read-side
689  * access to the pointer was removed at least one grace period ago, as
690  * is the case in the context of the RCU callback that is freeing up
691  * the data, or after a synchronize_rcu() returns.  This can be useful
692  * when tearing down multi-linked structures after a grace period
693  * has elapsed.
694  */
695 #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
696 
697 /**
698  * rcu_dereference_check() - rcu_dereference with debug checking
699  * @p: The pointer to read, prior to dereferencing
700  * @c: The conditions under which the dereference will take place
701  *
702  * Do an rcu_dereference(), but check that the conditions under which the
703  * dereference will take place are correct.  Typically the conditions
704  * indicate the various locking conditions that should be held at that
705  * point.  The check should return true if the conditions are satisfied.
706  * An implicit check for being in an RCU read-side critical section
707  * (rcu_read_lock()) is included.
708  *
709  * For example:
710  *
711  *      bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
712  *
713  * could be used to indicate to lockdep that foo->bar may only be dereferenced
714  * if either rcu_read_lock() is held, or that the lock required to replace
715  * the bar struct at foo->bar is held.
716  *
717  * Note that the list of conditions may also include indications of when a lock
718  * need not be held, for example during initialisation or destruction of the
719  * target struct:
720  *
721  *      bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
722  *                                            atomic_read(&foo->usage) == 0);
723  *
724  * Inserts memory barriers on architectures that require them
725  * (currently only the Alpha), prevents the compiler from refetching
726  * (and from merging fetches), and, more importantly, documents exactly
727  * which pointers are protected by RCU and checks that the pointer is
728  * annotated as __rcu.
729  */
730 #define rcu_dereference_check(p, c) \
731         __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
732 
733 /**
734  * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
735  * @p: The pointer to read, prior to dereferencing
736  * @c: The conditions under which the dereference will take place
737  *
738  * This is the RCU-bh counterpart to rcu_dereference_check().
739  */
740 #define rcu_dereference_bh_check(p, c) \
741         __rcu_dereference_check((p), (c) || rcu_read_lock_bh_held(), __rcu)
742 
743 /**
744  * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
745  * @p: The pointer to read, prior to dereferencing
746  * @c: The conditions under which the dereference will take place
747  *
748  * This is the RCU-sched counterpart to rcu_dereference_check().
749  */
750 #define rcu_dereference_sched_check(p, c) \
751         __rcu_dereference_check((p), (c) || rcu_read_lock_sched_held(), \
752                                 __rcu)
753 
754 /*
755  * The tracing infrastructure traces RCU (we want that), but unfortunately
756  * some of the RCU checks causes tracing to lock up the system.
757  *
758  * The no-tracing version of rcu_dereference_raw() must not call
759  * rcu_read_lock_held().
760  */
761 #define rcu_dereference_raw_notrace(p) __rcu_dereference_check((p), 1, __rcu)
762 
763 /**
764  * rcu_dereference_protected() - fetch RCU pointer when updates prevented
765  * @p: The pointer to read, prior to dereferencing
766  * @c: The conditions under which the dereference will take place
767  *
768  * Return the value of the specified RCU-protected pointer, but omit
769  * both the smp_read_barrier_depends() and the READ_ONCE().  This
770  * is useful in cases where update-side locks prevent the value of the
771  * pointer from changing.  Please note that this primitive does -not-
772  * prevent the compiler from repeating this reference or combining it
773  * with other references, so it should not be used without protection
774  * of appropriate locks.
775  *
776  * This function is only for update-side use.  Using this function
777  * when protected only by rcu_read_lock() will result in infrequent
778  * but very ugly failures.
779  */
780 #define rcu_dereference_protected(p, c) \
781         __rcu_dereference_protected((p), (c), __rcu)
782 
783 
784 /**
785  * rcu_dereference() - fetch RCU-protected pointer for dereferencing
786  * @p: The pointer to read, prior to dereferencing
787  *
788  * This is a simple wrapper around rcu_dereference_check().
789  */
790 #define rcu_dereference(p) rcu_dereference_check(p, 0)
791 
792 /**
793  * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
794  * @p: The pointer to read, prior to dereferencing
795  *
796  * Makes rcu_dereference_check() do the dirty work.
797  */
798 #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
799 
800 /**
801  * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
802  * @p: The pointer to read, prior to dereferencing
803  *
804  * Makes rcu_dereference_check() do the dirty work.
805  */
806 #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
807 
808 /**
809  * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism
810  * @p: The pointer to hand off
811  *
812  * This is simply an identity function, but it documents where a pointer
813  * is handed off from RCU to some other synchronization mechanism, for
814  * example, reference counting or locking.  In C11, it would map to
815  * kill_dependency().  It could be used as follows:
816  *
817  *      rcu_read_lock();
818  *      p = rcu_dereference(gp);
819  *      long_lived = is_long_lived(p);
820  *      if (long_lived) {
821  *              if (!atomic_inc_not_zero(p->refcnt))
822  *                      long_lived = false;
823  *              else
824  *                      p = rcu_pointer_handoff(p);
825  *      }
826  *      rcu_read_unlock();
827  */
828 #define rcu_pointer_handoff(p) (p)
829 
830 /**
831  * rcu_read_lock() - mark the beginning of an RCU read-side critical section
832  *
833  * When synchronize_rcu() is invoked on one CPU while other CPUs
834  * are within RCU read-side critical sections, then the
835  * synchronize_rcu() is guaranteed to block until after all the other
836  * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
837  * on one CPU while other CPUs are within RCU read-side critical
838  * sections, invocation of the corresponding RCU callback is deferred
839  * until after the all the other CPUs exit their critical sections.
840  *
841  * Note, however, that RCU callbacks are permitted to run concurrently
842  * with new RCU read-side critical sections.  One way that this can happen
843  * is via the following sequence of events: (1) CPU 0 enters an RCU
844  * read-side critical section, (2) CPU 1 invokes call_rcu() to register
845  * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
846  * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
847  * callback is invoked.  This is legal, because the RCU read-side critical
848  * section that was running concurrently with the call_rcu() (and which
849  * therefore might be referencing something that the corresponding RCU
850  * callback would free up) has completed before the corresponding
851  * RCU callback is invoked.
852  *
853  * RCU read-side critical sections may be nested.  Any deferred actions
854  * will be deferred until the outermost RCU read-side critical section
855  * completes.
856  *
857  * You can avoid reading and understanding the next paragraph by
858  * following this rule: don't put anything in an rcu_read_lock() RCU
859  * read-side critical section that would block in a !PREEMPT kernel.
860  * But if you want the full story, read on!
861  *
862  * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU),
863  * it is illegal to block while in an RCU read-side critical section.
864  * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPT
865  * kernel builds, RCU read-side critical sections may be preempted,
866  * but explicit blocking is illegal.  Finally, in preemptible RCU
867  * implementations in real-time (with -rt patchset) kernel builds, RCU
868  * read-side critical sections may be preempted and they may also block, but
869  * only when acquiring spinlocks that are subject to priority inheritance.
870  */
871 static inline void rcu_read_lock(void)
872 {
873         __rcu_read_lock();
874         __acquire(RCU);
875         rcu_lock_acquire(&rcu_lock_map);
876         RCU_LOCKDEP_WARN(!rcu_is_watching(),
877                          "rcu_read_lock() used illegally while idle");
878 }
879 
880 /*
881  * So where is rcu_write_lock()?  It does not exist, as there is no
882  * way for writers to lock out RCU readers.  This is a feature, not
883  * a bug -- this property is what provides RCU's performance benefits.
884  * Of course, writers must coordinate with each other.  The normal
885  * spinlock primitives work well for this, but any other technique may be
886  * used as well.  RCU does not care how the writers keep out of each
887  * others' way, as long as they do so.
888  */
889 
890 /**
891  * rcu_read_unlock() - marks the end of an RCU read-side critical section.
892  *
893  * In most situations, rcu_read_unlock() is immune from deadlock.
894  * However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock()
895  * is responsible for deboosting, which it does via rt_mutex_unlock().
896  * Unfortunately, this function acquires the scheduler's runqueue and
897  * priority-inheritance spinlocks.  This means that deadlock could result
898  * if the caller of rcu_read_unlock() already holds one of these locks or
899  * any lock that is ever acquired while holding them; or any lock which
900  * can be taken from interrupt context because rcu_boost()->rt_mutex_lock()
901  * does not disable irqs while taking ->wait_lock.
902  *
903  * That said, RCU readers are never priority boosted unless they were
904  * preempted.  Therefore, one way to avoid deadlock is to make sure
905  * that preemption never happens within any RCU read-side critical
906  * section whose outermost rcu_read_unlock() is called with one of
907  * rt_mutex_unlock()'s locks held.  Such preemption can be avoided in
908  * a number of ways, for example, by invoking preempt_disable() before
909  * critical section's outermost rcu_read_lock().
910  *
911  * Given that the set of locks acquired by rt_mutex_unlock() might change
912  * at any time, a somewhat more future-proofed approach is to make sure
913  * that that preemption never happens within any RCU read-side critical
914  * section whose outermost rcu_read_unlock() is called with irqs disabled.
915  * This approach relies on the fact that rt_mutex_unlock() currently only
916  * acquires irq-disabled locks.
917  *
918  * The second of these two approaches is best in most situations,
919  * however, the first approach can also be useful, at least to those
920  * developers willing to keep abreast of the set of locks acquired by
921  * rt_mutex_unlock().
922  *
923  * See rcu_read_lock() for more information.
924  */
925 static inline void rcu_read_unlock(void)
926 {
927         RCU_LOCKDEP_WARN(!rcu_is_watching(),
928                          "rcu_read_unlock() used illegally while idle");
929         __release(RCU);
930         __rcu_read_unlock();
931         rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
932 }
933 
934 /**
935  * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
936  *
937  * This is equivalent of rcu_read_lock(), but to be used when updates
938  * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since
939  * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a
940  * softirq handler to be a quiescent state, a process in RCU read-side
941  * critical section must be protected by disabling softirqs. Read-side
942  * critical sections in interrupt context can use just rcu_read_lock(),
943  * though this should at least be commented to avoid confusing people
944  * reading the code.
945  *
946  * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
947  * must occur in the same context, for example, it is illegal to invoke
948  * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
949  * was invoked from some other task.
950  */
951 static inline void rcu_read_lock_bh(void)
952 {
953         local_bh_disable();
954         __acquire(RCU_BH);
955         rcu_lock_acquire(&rcu_bh_lock_map);
956         RCU_LOCKDEP_WARN(!rcu_is_watching(),
957                          "rcu_read_lock_bh() used illegally while idle");
958 }
959 
960 /*
961  * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
962  *
963  * See rcu_read_lock_bh() for more information.
964  */
965 static inline void rcu_read_unlock_bh(void)
966 {
967         RCU_LOCKDEP_WARN(!rcu_is_watching(),
968                          "rcu_read_unlock_bh() used illegally while idle");
969         rcu_lock_release(&rcu_bh_lock_map);
970         __release(RCU_BH);
971         local_bh_enable();
972 }
973 
974 /**
975  * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
976  *
977  * This is equivalent of rcu_read_lock(), but to be used when updates
978  * are being done using call_rcu_sched() or synchronize_rcu_sched().
979  * Read-side critical sections can also be introduced by anything that
980  * disables preemption, including local_irq_disable() and friends.
981  *
982  * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
983  * must occur in the same context, for example, it is illegal to invoke
984  * rcu_read_unlock_sched() from process context if the matching
985  * rcu_read_lock_sched() was invoked from an NMI handler.
986  */
987 static inline void rcu_read_lock_sched(void)
988 {
989         preempt_disable();
990         __acquire(RCU_SCHED);
991         rcu_lock_acquire(&rcu_sched_lock_map);
992         RCU_LOCKDEP_WARN(!rcu_is_watching(),
993                          "rcu_read_lock_sched() used illegally while idle");
994 }
995 
996 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
997 static inline notrace void rcu_read_lock_sched_notrace(void)
998 {
999         preempt_disable_notrace();
1000         __acquire(RCU_SCHED);
1001 }
1002 
1003 /*
1004  * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
1005  *
1006  * See rcu_read_lock_sched for more information.
1007  */
1008 static inline void rcu_read_unlock_sched(void)
1009 {
1010         RCU_LOCKDEP_WARN(!rcu_is_watching(),
1011                          "rcu_read_unlock_sched() used illegally while idle");
1012         rcu_lock_release(&rcu_sched_lock_map);
1013         __release(RCU_SCHED);
1014         preempt_enable();
1015 }
1016 
1017 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
1018 static inline notrace void rcu_read_unlock_sched_notrace(void)
1019 {
1020         __release(RCU_SCHED);
1021         preempt_enable_notrace();
1022 }
1023 
1024 /**
1025  * RCU_INIT_POINTER() - initialize an RCU protected pointer
1026  *
1027  * Initialize an RCU-protected pointer in special cases where readers
1028  * do not need ordering constraints on the CPU or the compiler.  These
1029  * special cases are:
1030  *
1031  * 1.   This use of RCU_INIT_POINTER() is NULLing out the pointer -or-
1032  * 2.   The caller has taken whatever steps are required to prevent
1033  *      RCU readers from concurrently accessing this pointer -or-
1034  * 3.   The referenced data structure has already been exposed to
1035  *      readers either at compile time or via rcu_assign_pointer() -and-
1036  *      a.      You have not made -any- reader-visible changes to
1037  *              this structure since then -or-
1038  *      b.      It is OK for readers accessing this structure from its
1039  *              new location to see the old state of the structure.  (For
1040  *              example, the changes were to statistical counters or to
1041  *              other state where exact synchronization is not required.)
1042  *
1043  * Failure to follow these rules governing use of RCU_INIT_POINTER() will
1044  * result in impossible-to-diagnose memory corruption.  As in the structures
1045  * will look OK in crash dumps, but any concurrent RCU readers might
1046  * see pre-initialized values of the referenced data structure.  So
1047  * please be very careful how you use RCU_INIT_POINTER()!!!
1048  *
1049  * If you are creating an RCU-protected linked structure that is accessed
1050  * by a single external-to-structure RCU-protected pointer, then you may
1051  * use RCU_INIT_POINTER() to initialize the internal RCU-protected
1052  * pointers, but you must use rcu_assign_pointer() to initialize the
1053  * external-to-structure pointer -after- you have completely initialized
1054  * the reader-accessible portions of the linked structure.
1055  *
1056  * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
1057  * ordering guarantees for either the CPU or the compiler.
1058  */
1059 #define RCU_INIT_POINTER(p, v) \
1060         do { \
1061                 rcu_dereference_sparse(p, __rcu); \
1062                 WRITE_ONCE(p, RCU_INITIALIZER(v)); \
1063         } while (0)
1064 
1065 /**
1066  * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
1067  *
1068  * GCC-style initialization for an RCU-protected pointer in a structure field.
1069  */
1070 #define RCU_POINTER_INITIALIZER(p, v) \
1071                 .p = RCU_INITIALIZER(v)
1072 
1073 /*
1074  * Does the specified offset indicate that the corresponding rcu_head
1075  * structure can be handled by kfree_rcu()?
1076  */
1077 #define __is_kfree_rcu_offset(offset) ((offset) < 4096)
1078 
1079 /*
1080  * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain.
1081  */
1082 #define __kfree_rcu(head, offset) \
1083         do { \
1084                 BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \
1085                 kfree_call_rcu(head, (rcu_callback_t)(unsigned long)(offset)); \
1086         } while (0)
1087 
1088 /**
1089  * kfree_rcu() - kfree an object after a grace period.
1090  * @ptr:        pointer to kfree
1091  * @rcu_head:   the name of the struct rcu_head within the type of @ptr.
1092  *
1093  * Many rcu callbacks functions just call kfree() on the base structure.
1094  * These functions are trivial, but their size adds up, and furthermore
1095  * when they are used in a kernel module, that module must invoke the
1096  * high-latency rcu_barrier() function at module-unload time.
1097  *
1098  * The kfree_rcu() function handles this issue.  Rather than encoding a
1099  * function address in the embedded rcu_head structure, kfree_rcu() instead
1100  * encodes the offset of the rcu_head structure within the base structure.
1101  * Because the functions are not allowed in the low-order 4096 bytes of
1102  * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
1103  * If the offset is larger than 4095 bytes, a compile-time error will
1104  * be generated in __kfree_rcu().  If this error is triggered, you can
1105  * either fall back to use of call_rcu() or rearrange the structure to
1106  * position the rcu_head structure into the first 4096 bytes.
1107  *
1108  * Note that the allowable offset might decrease in the future, for example,
1109  * to allow something like kmem_cache_free_rcu().
1110  *
1111  * The BUILD_BUG_ON check must not involve any function calls, hence the
1112  * checks are done in macros here.
1113  */
1114 #define kfree_rcu(ptr, rcu_head)                                        \
1115         __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
1116 
1117 #ifdef CONFIG_TINY_RCU
1118 static inline int rcu_needs_cpu(u64 basemono, u64 *nextevt)
1119 {
1120         *nextevt = KTIME_MAX;
1121         return 0;
1122 }
1123 #endif /* #ifdef CONFIG_TINY_RCU */
1124 
1125 #if defined(CONFIG_RCU_NOCB_CPU_ALL)
1126 static inline bool rcu_is_nocb_cpu(int cpu) { return true; }
1127 #elif defined(CONFIG_RCU_NOCB_CPU)
1128 bool rcu_is_nocb_cpu(int cpu);
1129 #else
1130 static inline bool rcu_is_nocb_cpu(int cpu) { return false; }
1131 #endif
1132 
1133 
1134 /* Only for use by adaptive-ticks code. */
1135 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
1136 bool rcu_sys_is_idle(void);
1137 void rcu_sysidle_force_exit(void);
1138 #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
1139 
1140 static inline bool rcu_sys_is_idle(void)
1141 {
1142         return false;
1143 }
1144 
1145 static inline void rcu_sysidle_force_exit(void)
1146 {
1147 }
1148 
1149 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
1150 
1151 
1152 /*
1153  * Dump the ftrace buffer, but only one time per callsite per boot.
1154  */
1155 #define rcu_ftrace_dump(oops_dump_mode) \
1156 do { \
1157         static atomic_t ___rfd_beenhere = ATOMIC_INIT(0); \
1158         \
1159         if (!atomic_read(&___rfd_beenhere) && \
1160             !atomic_xchg(&___rfd_beenhere, 1)) \
1161                 ftrace_dump(oops_dump_mode); \
1162 } while (0)
1163 
1164 
1165 #endif /* __LINUX_RCUPDATE_H */
1166 

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