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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 <asm/barrier.h>
 48 
 49 extern int rcu_expedited; /* for sysctl */
 50 
 51 enum rcutorture_type {
 52         RCU_FLAVOR,
 53         RCU_BH_FLAVOR,
 54         RCU_SCHED_FLAVOR,
 55         RCU_TASKS_FLAVOR,
 56         SRCU_FLAVOR,
 57         INVALID_RCU_FLAVOR
 58 };
 59 
 60 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
 61 void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
 62                             unsigned long *gpnum, unsigned long *completed);
 63 void rcutorture_record_test_transition(void);
 64 void rcutorture_record_progress(unsigned long vernum);
 65 void do_trace_rcu_torture_read(const char *rcutorturename,
 66                                struct rcu_head *rhp,
 67                                unsigned long secs,
 68                                unsigned long c_old,
 69                                unsigned long c);
 70 #else
 71 static inline void rcutorture_get_gp_data(enum rcutorture_type test_type,
 72                                           int *flags,
 73                                           unsigned long *gpnum,
 74                                           unsigned long *completed)
 75 {
 76         *flags = 0;
 77         *gpnum = 0;
 78         *completed = 0;
 79 }
 80 static inline void rcutorture_record_test_transition(void)
 81 {
 82 }
 83 static inline void rcutorture_record_progress(unsigned long vernum)
 84 {
 85 }
 86 #ifdef CONFIG_RCU_TRACE
 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 #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
 94         do { } while (0)
 95 #endif
 96 #endif
 97 
 98 #define UINT_CMP_GE(a, b)       (UINT_MAX / 2 >= (a) - (b))
 99 #define UINT_CMP_LT(a, b)       (UINT_MAX / 2 < (a) - (b))
100 #define ULONG_CMP_GE(a, b)      (ULONG_MAX / 2 >= (a) - (b))
101 #define ULONG_CMP_LT(a, b)      (ULONG_MAX / 2 < (a) - (b))
102 #define ulong2long(a)           (*(long *)(&(a)))
103 
104 /* Exported common interfaces */
105 
106 #ifdef CONFIG_PREEMPT_RCU
107 
108 /**
109  * call_rcu() - Queue an RCU callback for invocation after a grace period.
110  * @head: structure to be used for queueing the RCU updates.
111  * @func: actual callback function to be invoked after the grace period
112  *
113  * The callback function will be invoked some time after a full grace
114  * period elapses, in other words after all pre-existing RCU read-side
115  * critical sections have completed.  However, the callback function
116  * might well execute concurrently with RCU read-side critical sections
117  * that started after call_rcu() was invoked.  RCU read-side critical
118  * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
119  * and may be nested.
120  *
121  * Note that all CPUs must agree that the grace period extended beyond
122  * all pre-existing RCU read-side critical section.  On systems with more
123  * than one CPU, this means that when "func()" is invoked, each CPU is
124  * guaranteed to have executed a full memory barrier since the end of its
125  * last RCU read-side critical section whose beginning preceded the call
126  * to call_rcu().  It also means that each CPU executing an RCU read-side
127  * critical section that continues beyond the start of "func()" must have
128  * executed a memory barrier after the call_rcu() but before the beginning
129  * of that RCU read-side critical section.  Note that these guarantees
130  * include CPUs that are offline, idle, or executing in user mode, as
131  * well as CPUs that are executing in the kernel.
132  *
133  * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
134  * resulting RCU callback function "func()", then both CPU A and CPU B are
135  * guaranteed to execute a full memory barrier during the time interval
136  * between the call to call_rcu() and the invocation of "func()" -- even
137  * if CPU A and CPU B are the same CPU (but again only if the system has
138  * more than one CPU).
139  */
140 void call_rcu(struct rcu_head *head,
141               void (*func)(struct rcu_head *head));
142 
143 #else /* #ifdef CONFIG_PREEMPT_RCU */
144 
145 /* In classic RCU, call_rcu() is just call_rcu_sched(). */
146 #define call_rcu        call_rcu_sched
147 
148 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
149 
150 /**
151  * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
152  * @head: structure to be used for queueing the RCU updates.
153  * @func: actual callback function to be invoked after the grace period
154  *
155  * The callback function will be invoked some time after a full grace
156  * period elapses, in other words after all currently executing RCU
157  * read-side critical sections have completed. call_rcu_bh() assumes
158  * that the read-side critical sections end on completion of a softirq
159  * handler. This means that read-side critical sections in process
160  * context must not be interrupted by softirqs. This interface is to be
161  * used when most of the read-side critical sections are in softirq context.
162  * RCU read-side critical sections are delimited by :
163  *  - rcu_read_lock() and  rcu_read_unlock(), if in interrupt context.
164  *  OR
165  *  - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
166  *  These may be nested.
167  *
168  * See the description of call_rcu() for more detailed information on
169  * memory ordering guarantees.
170  */
171 void call_rcu_bh(struct rcu_head *head,
172                  void (*func)(struct rcu_head *head));
173 
174 /**
175  * call_rcu_sched() - Queue an RCU for invocation after sched grace period.
176  * @head: structure to be used for queueing the RCU updates.
177  * @func: actual callback function to be invoked after the grace period
178  *
179  * The callback function will be invoked some time after a full grace
180  * period elapses, in other words after all currently executing RCU
181  * read-side critical sections have completed. call_rcu_sched() assumes
182  * that the read-side critical sections end on enabling of preemption
183  * or on voluntary preemption.
184  * RCU read-side critical sections are delimited by :
185  *  - rcu_read_lock_sched() and  rcu_read_unlock_sched(),
186  *  OR
187  *  anything that disables preemption.
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_sched(struct rcu_head *head,
194                     void (*func)(struct rcu_head *rcu));
195 
196 void synchronize_sched(void);
197 
198 /**
199  * call_rcu_tasks() - Queue an RCU for invocation task-based grace period
200  * @head: structure to be used for queueing the RCU updates.
201  * @func: actual callback function to be invoked after the grace period
202  *
203  * The callback function will be invoked some time after a full grace
204  * period elapses, in other words after all currently executing RCU
205  * read-side critical sections have completed. call_rcu_tasks() assumes
206  * that the read-side critical sections end at a voluntary context
207  * switch (not a preemption!), entry into idle, or transition to usermode
208  * execution.  As such, there are no read-side primitives analogous to
209  * rcu_read_lock() and rcu_read_unlock() because this primitive is intended
210  * to determine that all tasks have passed through a safe state, not so
211  * much for data-strcuture synchronization.
212  *
213  * See the description of call_rcu() for more detailed information on
214  * memory ordering guarantees.
215  */
216 void call_rcu_tasks(struct rcu_head *head, void (*func)(struct rcu_head *head));
217 void synchronize_rcu_tasks(void);
218 void rcu_barrier_tasks(void);
219 
220 #ifdef CONFIG_PREEMPT_RCU
221 
222 void __rcu_read_lock(void);
223 void __rcu_read_unlock(void);
224 void rcu_read_unlock_special(struct task_struct *t);
225 void synchronize_rcu(void);
226 
227 /*
228  * Defined as a macro as it is a very low level header included from
229  * areas that don't even know about current.  This gives the rcu_read_lock()
230  * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
231  * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
232  */
233 #define rcu_preempt_depth() (current->rcu_read_lock_nesting)
234 
235 #else /* #ifdef CONFIG_PREEMPT_RCU */
236 
237 static inline void __rcu_read_lock(void)
238 {
239         preempt_disable();
240 }
241 
242 static inline void __rcu_read_unlock(void)
243 {
244         preempt_enable();
245 }
246 
247 static inline void synchronize_rcu(void)
248 {
249         synchronize_sched();
250 }
251 
252 static inline int rcu_preempt_depth(void)
253 {
254         return 0;
255 }
256 
257 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
258 
259 /* Internal to kernel */
260 void rcu_init(void);
261 void rcu_sched_qs(void);
262 void rcu_bh_qs(void);
263 void rcu_check_callbacks(int user);
264 struct notifier_block;
265 void rcu_idle_enter(void);
266 void rcu_idle_exit(void);
267 void rcu_irq_enter(void);
268 void rcu_irq_exit(void);
269 
270 #ifdef CONFIG_RCU_STALL_COMMON
271 void rcu_sysrq_start(void);
272 void rcu_sysrq_end(void);
273 #else /* #ifdef CONFIG_RCU_STALL_COMMON */
274 static inline void rcu_sysrq_start(void)
275 {
276 }
277 static inline void rcu_sysrq_end(void)
278 {
279 }
280 #endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
281 
282 #ifdef CONFIG_RCU_USER_QS
283 void rcu_user_enter(void);
284 void rcu_user_exit(void);
285 #else
286 static inline void rcu_user_enter(void) { }
287 static inline void rcu_user_exit(void) { }
288 static inline void rcu_user_hooks_switch(struct task_struct *prev,
289                                          struct task_struct *next) { }
290 #endif /* CONFIG_RCU_USER_QS */
291 
292 #ifdef CONFIG_RCU_NOCB_CPU
293 void rcu_init_nohz(void);
294 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
295 static inline void rcu_init_nohz(void)
296 {
297 }
298 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
299 
300 /**
301  * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
302  * @a: Code that RCU needs to pay attention to.
303  *
304  * RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden
305  * in the inner idle loop, that is, between the rcu_idle_enter() and
306  * the rcu_idle_exit() -- RCU will happily ignore any such read-side
307  * critical sections.  However, things like powertop need tracepoints
308  * in the inner idle loop.
309  *
310  * This macro provides the way out:  RCU_NONIDLE(do_something_with_RCU())
311  * will tell RCU that it needs to pay attending, invoke its argument
312  * (in this example, a call to the do_something_with_RCU() function),
313  * and then tell RCU to go back to ignoring this CPU.  It is permissible
314  * to nest RCU_NONIDLE() wrappers, but the nesting level is currently
315  * quite limited.  If deeper nesting is required, it will be necessary
316  * to adjust DYNTICK_TASK_NESTING_VALUE accordingly.
317  */
318 #define RCU_NONIDLE(a) \
319         do { \
320                 rcu_irq_enter(); \
321                 do { a; } while (0); \
322                 rcu_irq_exit(); \
323         } while (0)
324 
325 /*
326  * Note a voluntary context switch for RCU-tasks benefit.  This is a
327  * macro rather than an inline function to avoid #include hell.
328  */
329 #ifdef CONFIG_TASKS_RCU
330 #define TASKS_RCU(x) x
331 extern struct srcu_struct tasks_rcu_exit_srcu;
332 #define rcu_note_voluntary_context_switch(t) \
333         do { \
334                 rcu_all_qs(); \
335                 if (ACCESS_ONCE((t)->rcu_tasks_holdout)) \
336                         ACCESS_ONCE((t)->rcu_tasks_holdout) = false; \
337         } while (0)
338 #else /* #ifdef CONFIG_TASKS_RCU */
339 #define TASKS_RCU(x) do { } while (0)
340 #define rcu_note_voluntary_context_switch(t)    rcu_all_qs()
341 #endif /* #else #ifdef CONFIG_TASKS_RCU */
342 
343 /**
344  * cond_resched_rcu_qs - Report potential quiescent states to RCU
345  *
346  * This macro resembles cond_resched(), except that it is defined to
347  * report potential quiescent states to RCU-tasks even if the cond_resched()
348  * machinery were to be shut off, as some advocate for PREEMPT kernels.
349  */
350 #define cond_resched_rcu_qs() \
351 do { \
352         if (!cond_resched()) \
353                 rcu_note_voluntary_context_switch(current); \
354 } while (0)
355 
356 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP)
357 bool __rcu_is_watching(void);
358 #endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP) */
359 
360 /*
361  * Infrastructure to implement the synchronize_() primitives in
362  * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
363  */
364 
365 typedef void call_rcu_func_t(struct rcu_head *head,
366                              void (*func)(struct rcu_head *head));
367 void wait_rcu_gp(call_rcu_func_t crf);
368 
369 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
370 #include <linux/rcutree.h>
371 #elif defined(CONFIG_TINY_RCU)
372 #include <linux/rcutiny.h>
373 #else
374 #error "Unknown RCU implementation specified to kernel configuration"
375 #endif
376 
377 /*
378  * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic
379  * initialization and destruction of rcu_head on the stack. rcu_head structures
380  * allocated dynamically in the heap or defined statically don't need any
381  * initialization.
382  */
383 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
384 void init_rcu_head(struct rcu_head *head);
385 void destroy_rcu_head(struct rcu_head *head);
386 void init_rcu_head_on_stack(struct rcu_head *head);
387 void destroy_rcu_head_on_stack(struct rcu_head *head);
388 #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
389 static inline void init_rcu_head(struct rcu_head *head)
390 {
391 }
392 
393 static inline void destroy_rcu_head(struct rcu_head *head)
394 {
395 }
396 
397 static inline void init_rcu_head_on_stack(struct rcu_head *head)
398 {
399 }
400 
401 static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
402 {
403 }
404 #endif  /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
405 
406 #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
407 bool rcu_lockdep_current_cpu_online(void);
408 #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
409 static inline bool rcu_lockdep_current_cpu_online(void)
410 {
411         return true;
412 }
413 #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
414 
415 #ifdef CONFIG_DEBUG_LOCK_ALLOC
416 
417 static inline void rcu_lock_acquire(struct lockdep_map *map)
418 {
419         lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
420 }
421 
422 static inline void rcu_lock_release(struct lockdep_map *map)
423 {
424         lock_release(map, 1, _THIS_IP_);
425 }
426 
427 extern struct lockdep_map rcu_lock_map;
428 extern struct lockdep_map rcu_bh_lock_map;
429 extern struct lockdep_map rcu_sched_lock_map;
430 extern struct lockdep_map rcu_callback_map;
431 int debug_lockdep_rcu_enabled(void);
432 
433 int rcu_read_lock_held(void);
434 int rcu_read_lock_bh_held(void);
435 
436 /**
437  * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
438  *
439  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
440  * RCU-sched read-side critical section.  In absence of
441  * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
442  * critical section unless it can prove otherwise.  Note that disabling
443  * of preemption (including disabling irqs) counts as an RCU-sched
444  * read-side critical section.  This is useful for debug checks in functions
445  * that required that they be called within an RCU-sched read-side
446  * critical section.
447  *
448  * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
449  * and while lockdep is disabled.
450  *
451  * Note that if the CPU is in the idle loop from an RCU point of
452  * view (ie: that we are in the section between rcu_idle_enter() and
453  * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
454  * did an rcu_read_lock().  The reason for this is that RCU ignores CPUs
455  * that are in such a section, considering these as in extended quiescent
456  * state, so such a CPU is effectively never in an RCU read-side critical
457  * section regardless of what RCU primitives it invokes.  This state of
458  * affairs is required --- we need to keep an RCU-free window in idle
459  * where the CPU may possibly enter into low power mode. This way we can
460  * notice an extended quiescent state to other CPUs that started a grace
461  * period. Otherwise we would delay any grace period as long as we run in
462  * the idle task.
463  *
464  * Similarly, we avoid claiming an SRCU read lock held if the current
465  * CPU is offline.
466  */
467 #ifdef CONFIG_PREEMPT_COUNT
468 static inline int rcu_read_lock_sched_held(void)
469 {
470         int lockdep_opinion = 0;
471 
472         if (!debug_lockdep_rcu_enabled())
473                 return 1;
474         if (!rcu_is_watching())
475                 return 0;
476         if (!rcu_lockdep_current_cpu_online())
477                 return 0;
478         if (debug_locks)
479                 lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
480         return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
481 }
482 #else /* #ifdef CONFIG_PREEMPT_COUNT */
483 static inline int rcu_read_lock_sched_held(void)
484 {
485         return 1;
486 }
487 #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
488 
489 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
490 
491 # define rcu_lock_acquire(a)            do { } while (0)
492 # define rcu_lock_release(a)            do { } while (0)
493 
494 static inline int rcu_read_lock_held(void)
495 {
496         return 1;
497 }
498 
499 static inline int rcu_read_lock_bh_held(void)
500 {
501         return 1;
502 }
503 
504 #ifdef CONFIG_PREEMPT_COUNT
505 static inline int rcu_read_lock_sched_held(void)
506 {
507         return preempt_count() != 0 || irqs_disabled();
508 }
509 #else /* #ifdef CONFIG_PREEMPT_COUNT */
510 static inline int rcu_read_lock_sched_held(void)
511 {
512         return 1;
513 }
514 #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
515 
516 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
517 
518 #ifdef CONFIG_PROVE_RCU
519 
520 /**
521  * rcu_lockdep_assert - emit lockdep splat if specified condition not met
522  * @c: condition to check
523  * @s: informative message
524  */
525 #define rcu_lockdep_assert(c, s)                                        \
526         do {                                                            \
527                 static bool __section(.data.unlikely) __warned;         \
528                 if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
529                         __warned = true;                                \
530                         lockdep_rcu_suspicious(__FILE__, __LINE__, s);  \
531                 }                                                       \
532         } while (0)
533 
534 #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
535 static inline void rcu_preempt_sleep_check(void)
536 {
537         rcu_lockdep_assert(!lock_is_held(&rcu_lock_map),
538                            "Illegal context switch in RCU read-side critical section");
539 }
540 #else /* #ifdef CONFIG_PROVE_RCU */
541 static inline void rcu_preempt_sleep_check(void)
542 {
543 }
544 #endif /* #else #ifdef CONFIG_PROVE_RCU */
545 
546 #define rcu_sleep_check()                                               \
547         do {                                                            \
548                 rcu_preempt_sleep_check();                              \
549                 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map),     \
550                                    "Illegal context switch in RCU-bh read-side critical section"); \
551                 rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map),  \
552                                    "Illegal context switch in RCU-sched read-side critical section"); \
553         } while (0)
554 
555 #else /* #ifdef CONFIG_PROVE_RCU */
556 
557 #define rcu_lockdep_assert(c, s) do { } while (0)
558 #define rcu_sleep_check() do { } while (0)
559 
560 #endif /* #else #ifdef CONFIG_PROVE_RCU */
561 
562 /*
563  * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
564  * and rcu_assign_pointer().  Some of these could be folded into their
565  * callers, but they are left separate in order to ease introduction of
566  * multiple flavors of pointers to match the multiple flavors of RCU
567  * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in
568  * the future.
569  */
570 
571 #ifdef __CHECKER__
572 #define rcu_dereference_sparse(p, space) \
573         ((void)(((typeof(*p) space *)p) == p))
574 #else /* #ifdef __CHECKER__ */
575 #define rcu_dereference_sparse(p, space)
576 #endif /* #else #ifdef __CHECKER__ */
577 
578 #define __rcu_access_pointer(p, space) \
579 ({ \
580         typeof(*p) *_________p1 = (typeof(*p) *__force)ACCESS_ONCE(p); \
581         rcu_dereference_sparse(p, space); \
582         ((typeof(*p) __force __kernel *)(_________p1)); \
583 })
584 #define __rcu_dereference_check(p, c, space) \
585 ({ \
586         /* Dependency order vs. p above. */ \
587         typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \
588         rcu_lockdep_assert(c, "suspicious rcu_dereference_check() usage"); \
589         rcu_dereference_sparse(p, space); \
590         ((typeof(*p) __force __kernel *)(________p1)); \
591 })
592 #define __rcu_dereference_protected(p, c, space) \
593 ({ \
594         rcu_lockdep_assert(c, "suspicious rcu_dereference_protected() usage"); \
595         rcu_dereference_sparse(p, space); \
596         ((typeof(*p) __force __kernel *)(p)); \
597 })
598 
599 #define __rcu_access_index(p, space) \
600 ({ \
601         typeof(p) _________p1 = ACCESS_ONCE(p); \
602         rcu_dereference_sparse(p, space); \
603         (_________p1); \
604 })
605 #define __rcu_dereference_index_check(p, c) \
606 ({ \
607         /* Dependency order vs. p above. */ \
608         typeof(p) _________p1 = lockless_dereference(p); \
609         rcu_lockdep_assert(c, \
610                            "suspicious rcu_dereference_index_check() usage"); \
611         (_________p1); \
612 })
613 
614 /**
615  * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
616  * @v: The value to statically initialize with.
617  */
618 #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
619 
620 /**
621  * lockless_dereference() - safely load a pointer for later dereference
622  * @p: The pointer to load
623  *
624  * Similar to rcu_dereference(), but for situations where the pointed-to
625  * object's lifetime is managed by something other than RCU.  That
626  * "something other" might be reference counting or simple immortality.
627  */
628 #define lockless_dereference(p) \
629 ({ \
630         typeof(p) _________p1 = ACCESS_ONCE(p); \
631         smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
632         (_________p1); \
633 })
634 
635 /**
636  * rcu_assign_pointer() - assign to RCU-protected pointer
637  * @p: pointer to assign to
638  * @v: value to assign (publish)
639  *
640  * Assigns the specified value to the specified RCU-protected
641  * pointer, ensuring that any concurrent RCU readers will see
642  * any prior initialization.
643  *
644  * Inserts memory barriers on architectures that require them
645  * (which is most of them), and also prevents the compiler from
646  * reordering the code that initializes the structure after the pointer
647  * assignment.  More importantly, this call documents which pointers
648  * will be dereferenced by RCU read-side code.
649  *
650  * In some special cases, you may use RCU_INIT_POINTER() instead
651  * of rcu_assign_pointer().  RCU_INIT_POINTER() is a bit faster due
652  * to the fact that it does not constrain either the CPU or the compiler.
653  * That said, using RCU_INIT_POINTER() when you should have used
654  * rcu_assign_pointer() is a very bad thing that results in
655  * impossible-to-diagnose memory corruption.  So please be careful.
656  * See the RCU_INIT_POINTER() comment header for details.
657  *
658  * Note that rcu_assign_pointer() evaluates each of its arguments only
659  * once, appearances notwithstanding.  One of the "extra" evaluations
660  * is in typeof() and the other visible only to sparse (__CHECKER__),
661  * neither of which actually execute the argument.  As with most cpp
662  * macros, this execute-arguments-only-once property is important, so
663  * please be careful when making changes to rcu_assign_pointer() and the
664  * other macros that it invokes.
665  */
666 #define rcu_assign_pointer(p, v) smp_store_release(&p, RCU_INITIALIZER(v))
667 
668 /**
669  * rcu_access_pointer() - fetch RCU pointer with no dereferencing
670  * @p: The pointer to read
671  *
672  * Return the value of the specified RCU-protected pointer, but omit the
673  * smp_read_barrier_depends() and keep the ACCESS_ONCE().  This is useful
674  * when the value of this pointer is accessed, but the pointer is not
675  * dereferenced, for example, when testing an RCU-protected pointer against
676  * NULL.  Although rcu_access_pointer() may also be used in cases where
677  * update-side locks prevent the value of the pointer from changing, you
678  * should instead use rcu_dereference_protected() for this use case.
679  *
680  * It is also permissible to use rcu_access_pointer() when read-side
681  * access to the pointer was removed at least one grace period ago, as
682  * is the case in the context of the RCU callback that is freeing up
683  * the data, or after a synchronize_rcu() returns.  This can be useful
684  * when tearing down multi-linked structures after a grace period
685  * has elapsed.
686  */
687 #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
688 
689 /**
690  * rcu_dereference_check() - rcu_dereference with debug checking
691  * @p: The pointer to read, prior to dereferencing
692  * @c: The conditions under which the dereference will take place
693  *
694  * Do an rcu_dereference(), but check that the conditions under which the
695  * dereference will take place are correct.  Typically the conditions
696  * indicate the various locking conditions that should be held at that
697  * point.  The check should return true if the conditions are satisfied.
698  * An implicit check for being in an RCU read-side critical section
699  * (rcu_read_lock()) is included.
700  *
701  * For example:
702  *
703  *      bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
704  *
705  * could be used to indicate to lockdep that foo->bar may only be dereferenced
706  * if either rcu_read_lock() is held, or that the lock required to replace
707  * the bar struct at foo->bar is held.
708  *
709  * Note that the list of conditions may also include indications of when a lock
710  * need not be held, for example during initialisation or destruction of the
711  * target struct:
712  *
713  *      bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
714  *                                            atomic_read(&foo->usage) == 0);
715  *
716  * Inserts memory barriers on architectures that require them
717  * (currently only the Alpha), prevents the compiler from refetching
718  * (and from merging fetches), and, more importantly, documents exactly
719  * which pointers are protected by RCU and checks that the pointer is
720  * annotated as __rcu.
721  */
722 #define rcu_dereference_check(p, c) \
723         __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)
724 
725 /**
726  * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
727  * @p: The pointer to read, prior to dereferencing
728  * @c: The conditions under which the dereference will take place
729  *
730  * This is the RCU-bh counterpart to rcu_dereference_check().
731  */
732 #define rcu_dereference_bh_check(p, c) \
733         __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu)
734 
735 /**
736  * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
737  * @p: The pointer to read, prior to dereferencing
738  * @c: The conditions under which the dereference will take place
739  *
740  * This is the RCU-sched counterpart to rcu_dereference_check().
741  */
742 #define rcu_dereference_sched_check(p, c) \
743         __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \
744                                 __rcu)
745 
746 #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/
747 
748 /*
749  * The tracing infrastructure traces RCU (we want that), but unfortunately
750  * some of the RCU checks causes tracing to lock up the system.
751  *
752  * The tracing version of rcu_dereference_raw() must not call
753  * rcu_read_lock_held().
754  */
755 #define rcu_dereference_raw_notrace(p) __rcu_dereference_check((p), 1, __rcu)
756 
757 /**
758  * rcu_access_index() - fetch RCU index with no dereferencing
759  * @p: The index to read
760  *
761  * Return the value of the specified RCU-protected index, but omit the
762  * smp_read_barrier_depends() and keep the ACCESS_ONCE().  This is useful
763  * when the value of this index is accessed, but the index is not
764  * dereferenced, for example, when testing an RCU-protected index against
765  * -1.  Although rcu_access_index() may also be used in cases where
766  * update-side locks prevent the value of the index from changing, you
767  * should instead use rcu_dereference_index_protected() for this use case.
768  */
769 #define rcu_access_index(p) __rcu_access_index((p), __rcu)
770 
771 /**
772  * rcu_dereference_index_check() - rcu_dereference for indices with debug checking
773  * @p: The pointer to read, prior to dereferencing
774  * @c: The conditions under which the dereference will take place
775  *
776  * Similar to rcu_dereference_check(), but omits the sparse checking.
777  * This allows rcu_dereference_index_check() to be used on integers,
778  * which can then be used as array indices.  Attempting to use
779  * rcu_dereference_check() on an integer will give compiler warnings
780  * because the sparse address-space mechanism relies on dereferencing
781  * the RCU-protected pointer.  Dereferencing integers is not something
782  * that even gcc will put up with.
783  *
784  * Note that this function does not implicitly check for RCU read-side
785  * critical sections.  If this function gains lots of uses, it might
786  * make sense to provide versions for each flavor of RCU, but it does
787  * not make sense as of early 2010.
788  */
789 #define rcu_dereference_index_check(p, c) \
790         __rcu_dereference_index_check((p), (c))
791 
792 /**
793  * rcu_dereference_protected() - fetch RCU pointer when updates prevented
794  * @p: The pointer to read, prior to dereferencing
795  * @c: The conditions under which the dereference will take place
796  *
797  * Return the value of the specified RCU-protected pointer, but omit
798  * both the smp_read_barrier_depends() and the ACCESS_ONCE().  This
799  * is useful in cases where update-side locks prevent the value of the
800  * pointer from changing.  Please note that this primitive does -not-
801  * prevent the compiler from repeating this reference or combining it
802  * with other references, so it should not be used without protection
803  * of appropriate locks.
804  *
805  * This function is only for update-side use.  Using this function
806  * when protected only by rcu_read_lock() will result in infrequent
807  * but very ugly failures.
808  */
809 #define rcu_dereference_protected(p, c) \
810         __rcu_dereference_protected((p), (c), __rcu)
811 
812 
813 /**
814  * rcu_dereference() - fetch RCU-protected pointer for dereferencing
815  * @p: The pointer to read, prior to dereferencing
816  *
817  * This is a simple wrapper around rcu_dereference_check().
818  */
819 #define rcu_dereference(p) rcu_dereference_check(p, 0)
820 
821 /**
822  * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
823  * @p: The pointer to read, prior to dereferencing
824  *
825  * Makes rcu_dereference_check() do the dirty work.
826  */
827 #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
828 
829 /**
830  * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
831  * @p: The pointer to read, prior to dereferencing
832  *
833  * Makes rcu_dereference_check() do the dirty work.
834  */
835 #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
836 
837 /**
838  * rcu_read_lock() - mark the beginning of an RCU read-side critical section
839  *
840  * When synchronize_rcu() is invoked on one CPU while other CPUs
841  * are within RCU read-side critical sections, then the
842  * synchronize_rcu() is guaranteed to block until after all the other
843  * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
844  * on one CPU while other CPUs are within RCU read-side critical
845  * sections, invocation of the corresponding RCU callback is deferred
846  * until after the all the other CPUs exit their critical sections.
847  *
848  * Note, however, that RCU callbacks are permitted to run concurrently
849  * with new RCU read-side critical sections.  One way that this can happen
850  * is via the following sequence of events: (1) CPU 0 enters an RCU
851  * read-side critical section, (2) CPU 1 invokes call_rcu() to register
852  * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
853  * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
854  * callback is invoked.  This is legal, because the RCU read-side critical
855  * section that was running concurrently with the call_rcu() (and which
856  * therefore might be referencing something that the corresponding RCU
857  * callback would free up) has completed before the corresponding
858  * RCU callback is invoked.
859  *
860  * RCU read-side critical sections may be nested.  Any deferred actions
861  * will be deferred until the outermost RCU read-side critical section
862  * completes.
863  *
864  * You can avoid reading and understanding the next paragraph by
865  * following this rule: don't put anything in an rcu_read_lock() RCU
866  * read-side critical section that would block in a !PREEMPT kernel.
867  * But if you want the full story, read on!
868  *
869  * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU),
870  * it is illegal to block while in an RCU read-side critical section.
871  * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPT
872  * kernel builds, RCU read-side critical sections may be preempted,
873  * but explicit blocking is illegal.  Finally, in preemptible RCU
874  * implementations in real-time (with -rt patchset) kernel builds, RCU
875  * read-side critical sections may be preempted and they may also block, but
876  * only when acquiring spinlocks that are subject to priority inheritance.
877  */
878 static inline void rcu_read_lock(void)
879 {
880         __rcu_read_lock();
881         __acquire(RCU);
882         rcu_lock_acquire(&rcu_lock_map);
883         rcu_lockdep_assert(rcu_is_watching(),
884                            "rcu_read_lock() used illegally while idle");
885 }
886 
887 /*
888  * So where is rcu_write_lock()?  It does not exist, as there is no
889  * way for writers to lock out RCU readers.  This is a feature, not
890  * a bug -- this property is what provides RCU's performance benefits.
891  * Of course, writers must coordinate with each other.  The normal
892  * spinlock primitives work well for this, but any other technique may be
893  * used as well.  RCU does not care how the writers keep out of each
894  * others' way, as long as they do so.
895  */
896 
897 /**
898  * rcu_read_unlock() - marks the end of an RCU read-side critical section.
899  *
900  * In most situations, rcu_read_unlock() is immune from deadlock.
901  * However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock()
902  * is responsible for deboosting, which it does via rt_mutex_unlock().
903  * Unfortunately, this function acquires the scheduler's runqueue and
904  * priority-inheritance spinlocks.  This means that deadlock could result
905  * if the caller of rcu_read_unlock() already holds one of these locks or
906  * any lock that is ever acquired while holding them; or any lock which
907  * can be taken from interrupt context because rcu_boost()->rt_mutex_lock()
908  * does not disable irqs while taking ->wait_lock.
909  *
910  * That said, RCU readers are never priority boosted unless they were
911  * preempted.  Therefore, one way to avoid deadlock is to make sure
912  * that preemption never happens within any RCU read-side critical
913  * section whose outermost rcu_read_unlock() is called with one of
914  * rt_mutex_unlock()'s locks held.  Such preemption can be avoided in
915  * a number of ways, for example, by invoking preempt_disable() before
916  * critical section's outermost rcu_read_lock().
917  *
918  * Given that the set of locks acquired by rt_mutex_unlock() might change
919  * at any time, a somewhat more future-proofed approach is to make sure
920  * that that preemption never happens within any RCU read-side critical
921  * section whose outermost rcu_read_unlock() is called with irqs disabled.
922  * This approach relies on the fact that rt_mutex_unlock() currently only
923  * acquires irq-disabled locks.
924  *
925  * The second of these two approaches is best in most situations,
926  * however, the first approach can also be useful, at least to those
927  * developers willing to keep abreast of the set of locks acquired by
928  * rt_mutex_unlock().
929  *
930  * See rcu_read_lock() for more information.
931  */
932 static inline void rcu_read_unlock(void)
933 {
934         rcu_lockdep_assert(rcu_is_watching(),
935                            "rcu_read_unlock() used illegally while idle");
936         rcu_lock_release(&rcu_lock_map);
937         __release(RCU);
938         __rcu_read_unlock();
939 }
940 
941 /**
942  * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
943  *
944  * This is equivalent of rcu_read_lock(), but to be used when updates
945  * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since
946  * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a
947  * softirq handler to be a quiescent state, a process in RCU read-side
948  * critical section must be protected by disabling softirqs. Read-side
949  * critical sections in interrupt context can use just rcu_read_lock(),
950  * though this should at least be commented to avoid confusing people
951  * reading the code.
952  *
953  * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
954  * must occur in the same context, for example, it is illegal to invoke
955  * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
956  * was invoked from some other task.
957  */
958 static inline void rcu_read_lock_bh(void)
959 {
960         local_bh_disable();
961         __acquire(RCU_BH);
962         rcu_lock_acquire(&rcu_bh_lock_map);
963         rcu_lockdep_assert(rcu_is_watching(),
964                            "rcu_read_lock_bh() used illegally while idle");
965 }
966 
967 /*
968  * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
969  *
970  * See rcu_read_lock_bh() for more information.
971  */
972 static inline void rcu_read_unlock_bh(void)
973 {
974         rcu_lockdep_assert(rcu_is_watching(),
975                            "rcu_read_unlock_bh() used illegally while idle");
976         rcu_lock_release(&rcu_bh_lock_map);
977         __release(RCU_BH);
978         local_bh_enable();
979 }
980 
981 /**
982  * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
983  *
984  * This is equivalent of rcu_read_lock(), but to be used when updates
985  * are being done using call_rcu_sched() or synchronize_rcu_sched().
986  * Read-side critical sections can also be introduced by anything that
987  * disables preemption, including local_irq_disable() and friends.
988  *
989  * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
990  * must occur in the same context, for example, it is illegal to invoke
991  * rcu_read_unlock_sched() from process context if the matching
992  * rcu_read_lock_sched() was invoked from an NMI handler.
993  */
994 static inline void rcu_read_lock_sched(void)
995 {
996         preempt_disable();
997         __acquire(RCU_SCHED);
998         rcu_lock_acquire(&rcu_sched_lock_map);
999         rcu_lockdep_assert(rcu_is_watching(),
1000                            "rcu_read_lock_sched() used illegally while idle");
1001 }
1002 
1003 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
1004 static inline notrace void rcu_read_lock_sched_notrace(void)
1005 {
1006         preempt_disable_notrace();
1007         __acquire(RCU_SCHED);
1008 }
1009 
1010 /*
1011  * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
1012  *
1013  * See rcu_read_lock_sched for more information.
1014  */
1015 static inline void rcu_read_unlock_sched(void)
1016 {
1017         rcu_lockdep_assert(rcu_is_watching(),
1018                            "rcu_read_unlock_sched() used illegally while idle");
1019         rcu_lock_release(&rcu_sched_lock_map);
1020         __release(RCU_SCHED);
1021         preempt_enable();
1022 }
1023 
1024 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
1025 static inline notrace void rcu_read_unlock_sched_notrace(void)
1026 {
1027         __release(RCU_SCHED);
1028         preempt_enable_notrace();
1029 }
1030 
1031 /**
1032  * RCU_INIT_POINTER() - initialize an RCU protected pointer
1033  *
1034  * Initialize an RCU-protected pointer in special cases where readers
1035  * do not need ordering constraints on the CPU or the compiler.  These
1036  * special cases are:
1037  *
1038  * 1.   This use of RCU_INIT_POINTER() is NULLing out the pointer -or-
1039  * 2.   The caller has taken whatever steps are required to prevent
1040  *      RCU readers from concurrently accessing this pointer -or-
1041  * 3.   The referenced data structure has already been exposed to
1042  *      readers either at compile time or via rcu_assign_pointer() -and-
1043  *      a.      You have not made -any- reader-visible changes to
1044  *              this structure since then -or-
1045  *      b.      It is OK for readers accessing this structure from its
1046  *              new location to see the old state of the structure.  (For
1047  *              example, the changes were to statistical counters or to
1048  *              other state where exact synchronization is not required.)
1049  *
1050  * Failure to follow these rules governing use of RCU_INIT_POINTER() will
1051  * result in impossible-to-diagnose memory corruption.  As in the structures
1052  * will look OK in crash dumps, but any concurrent RCU readers might
1053  * see pre-initialized values of the referenced data structure.  So
1054  * please be very careful how you use RCU_INIT_POINTER()!!!
1055  *
1056  * If you are creating an RCU-protected linked structure that is accessed
1057  * by a single external-to-structure RCU-protected pointer, then you may
1058  * use RCU_INIT_POINTER() to initialize the internal RCU-protected
1059  * pointers, but you must use rcu_assign_pointer() to initialize the
1060  * external-to-structure pointer -after- you have completely initialized
1061  * the reader-accessible portions of the linked structure.
1062  *
1063  * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
1064  * ordering guarantees for either the CPU or the compiler.
1065  */
1066 #define RCU_INIT_POINTER(p, v) \
1067         do { \
1068                 rcu_dereference_sparse(p, __rcu); \
1069                 p = RCU_INITIALIZER(v); \
1070         } while (0)
1071 
1072 /**
1073  * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
1074  *
1075  * GCC-style initialization for an RCU-protected pointer in a structure field.
1076  */
1077 #define RCU_POINTER_INITIALIZER(p, v) \
1078                 .p = RCU_INITIALIZER(v)
1079 
1080 /*
1081  * Does the specified offset indicate that the corresponding rcu_head
1082  * structure can be handled by kfree_rcu()?
1083  */
1084 #define __is_kfree_rcu_offset(offset) ((offset) < 4096)
1085 
1086 /*
1087  * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain.
1088  */
1089 #define __kfree_rcu(head, offset) \
1090         do { \
1091                 BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \
1092                 kfree_call_rcu(head, (void (*)(struct rcu_head *))(unsigned long)(offset)); \
1093         } while (0)
1094 
1095 /**
1096  * kfree_rcu() - kfree an object after a grace period.
1097  * @ptr:        pointer to kfree
1098  * @rcu_head:   the name of the struct rcu_head within the type of @ptr.
1099  *
1100  * Many rcu callbacks functions just call kfree() on the base structure.
1101  * These functions are trivial, but their size adds up, and furthermore
1102  * when they are used in a kernel module, that module must invoke the
1103  * high-latency rcu_barrier() function at module-unload time.
1104  *
1105  * The kfree_rcu() function handles this issue.  Rather than encoding a
1106  * function address in the embedded rcu_head structure, kfree_rcu() instead
1107  * encodes the offset of the rcu_head structure within the base structure.
1108  * Because the functions are not allowed in the low-order 4096 bytes of
1109  * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
1110  * If the offset is larger than 4095 bytes, a compile-time error will
1111  * be generated in __kfree_rcu().  If this error is triggered, you can
1112  * either fall back to use of call_rcu() or rearrange the structure to
1113  * position the rcu_head structure into the first 4096 bytes.
1114  *
1115  * Note that the allowable offset might decrease in the future, for example,
1116  * to allow something like kmem_cache_free_rcu().
1117  *
1118  * The BUILD_BUG_ON check must not involve any function calls, hence the
1119  * checks are done in macros here.
1120  */
1121 #define kfree_rcu(ptr, rcu_head)                                        \
1122         __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
1123 
1124 #if defined(CONFIG_TINY_RCU) || defined(CONFIG_RCU_NOCB_CPU_ALL)
1125 static inline int rcu_needs_cpu(unsigned long *delta_jiffies)
1126 {
1127         *delta_jiffies = ULONG_MAX;
1128         return 0;
1129 }
1130 #endif /* #if defined(CONFIG_TINY_RCU) || defined(CONFIG_RCU_NOCB_CPU_ALL) */
1131 
1132 #if defined(CONFIG_RCU_NOCB_CPU_ALL)
1133 static inline bool rcu_is_nocb_cpu(int cpu) { return true; }
1134 #elif defined(CONFIG_RCU_NOCB_CPU)
1135 bool rcu_is_nocb_cpu(int cpu);
1136 #else
1137 static inline bool rcu_is_nocb_cpu(int cpu) { return false; }
1138 #endif
1139 
1140 
1141 /* Only for use by adaptive-ticks code. */
1142 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
1143 bool rcu_sys_is_idle(void);
1144 void rcu_sysidle_force_exit(void);
1145 #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
1146 
1147 static inline bool rcu_sys_is_idle(void)
1148 {
1149         return false;
1150 }
1151 
1152 static inline void rcu_sysidle_force_exit(void)
1153 {
1154 }
1155 
1156 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
1157 
1158 
1159 #endif /* __LINUX_RCUPDATE_H */
1160 

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