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

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