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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 #ifdef CONFIG_RCU_TORTURE_TEST
 51 extern int rcutorture_runnable; /* for sysctl */
 52 #endif /* #ifdef CONFIG_RCU_TORTURE_TEST */
 53 
 54 enum rcutorture_type {
 55         RCU_FLAVOR,
 56         RCU_BH_FLAVOR,
 57         RCU_SCHED_FLAVOR,
 58         SRCU_FLAVOR,
 59         INVALID_RCU_FLAVOR
 60 };
 61 
 62 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
 63 void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
 64                             unsigned long *gpnum, unsigned long *completed);
 65 void rcutorture_record_test_transition(void);
 66 void rcutorture_record_progress(unsigned long vernum);
 67 void do_trace_rcu_torture_read(const char *rcutorturename,
 68                                struct rcu_head *rhp,
 69                                unsigned long secs,
 70                                unsigned long c_old,
 71                                unsigned long c);
 72 #else
 73 static inline void rcutorture_get_gp_data(enum rcutorture_type test_type,
 74                                           int *flags,
 75                                           unsigned long *gpnum,
 76                                           unsigned long *completed)
 77 {
 78         *flags = 0;
 79         *gpnum = 0;
 80         *completed = 0;
 81 }
 82 static inline void rcutorture_record_test_transition(void)
 83 {
 84 }
 85 static inline void rcutorture_record_progress(unsigned long vernum)
 86 {
 87 }
 88 #ifdef CONFIG_RCU_TRACE
 89 void do_trace_rcu_torture_read(const char *rcutorturename,
 90                                struct rcu_head *rhp,
 91                                unsigned long secs,
 92                                unsigned long c_old,
 93                                unsigned long c);
 94 #else
 95 #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
 96         do { } while (0)
 97 #endif
 98 #endif
 99 
100 #define UINT_CMP_GE(a, b)       (UINT_MAX / 2 >= (a) - (b))
101 #define UINT_CMP_LT(a, b)       (UINT_MAX / 2 < (a) - (b))
102 #define ULONG_CMP_GE(a, b)      (ULONG_MAX / 2 >= (a) - (b))
103 #define ULONG_CMP_LT(a, b)      (ULONG_MAX / 2 < (a) - (b))
104 #define ulong2long(a)           (*(long *)(&(a)))
105 
106 /* Exported common interfaces */
107 
108 #ifdef CONFIG_PREEMPT_RCU
109 
110 /**
111  * call_rcu() - Queue an RCU callback for invocation after a grace period.
112  * @head: structure to be used for queueing the RCU updates.
113  * @func: actual callback function to be invoked after the grace period
114  *
115  * The callback function will be invoked some time after a full grace
116  * period elapses, in other words after all pre-existing RCU read-side
117  * critical sections have completed.  However, the callback function
118  * might well execute concurrently with RCU read-side critical sections
119  * that started after call_rcu() was invoked.  RCU read-side critical
120  * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
121  * and may be nested.
122  *
123  * Note that all CPUs must agree that the grace period extended beyond
124  * all pre-existing RCU read-side critical section.  On systems with more
125  * than one CPU, this means that when "func()" is invoked, each CPU is
126  * guaranteed to have executed a full memory barrier since the end of its
127  * last RCU read-side critical section whose beginning preceded the call
128  * to call_rcu().  It also means that each CPU executing an RCU read-side
129  * critical section that continues beyond the start of "func()" must have
130  * executed a memory barrier after the call_rcu() but before the beginning
131  * of that RCU read-side critical section.  Note that these guarantees
132  * include CPUs that are offline, idle, or executing in user mode, as
133  * well as CPUs that are executing in the kernel.
134  *
135  * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
136  * resulting RCU callback function "func()", then both CPU A and CPU B are
137  * guaranteed to execute a full memory barrier during the time interval
138  * between the call to call_rcu() and the invocation of "func()" -- even
139  * if CPU A and CPU B are the same CPU (but again only if the system has
140  * more than one CPU).
141  */
142 void call_rcu(struct rcu_head *head,
143               void (*func)(struct rcu_head *head));
144 
145 #else /* #ifdef CONFIG_PREEMPT_RCU */
146 
147 /* In classic RCU, call_rcu() is just call_rcu_sched(). */
148 #define call_rcu        call_rcu_sched
149 
150 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
151 
152 /**
153  * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
154  * @head: structure to be used for queueing the RCU updates.
155  * @func: actual callback function to be invoked after the grace period
156  *
157  * The callback function will be invoked some time after a full grace
158  * period elapses, in other words after all currently executing RCU
159  * read-side critical sections have completed. call_rcu_bh() assumes
160  * that the read-side critical sections end on completion of a softirq
161  * handler. This means that read-side critical sections in process
162  * context must not be interrupted by softirqs. This interface is to be
163  * used when most of the read-side critical sections are in softirq context.
164  * RCU read-side critical sections are delimited by :
165  *  - rcu_read_lock() and  rcu_read_unlock(), if in interrupt context.
166  *  OR
167  *  - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
168  *  These may be nested.
169  *
170  * See the description of call_rcu() for more detailed information on
171  * memory ordering guarantees.
172  */
173 void call_rcu_bh(struct rcu_head *head,
174                  void (*func)(struct rcu_head *head));
175 
176 /**
177  * call_rcu_sched() - Queue an RCU for invocation after sched grace period.
178  * @head: structure to be used for queueing the RCU updates.
179  * @func: actual callback function to be invoked after the grace period
180  *
181  * The callback function will be invoked some time after a full grace
182  * period elapses, in other words after all currently executing RCU
183  * read-side critical sections have completed. call_rcu_sched() assumes
184  * that the read-side critical sections end on enabling of preemption
185  * or on voluntary preemption.
186  * RCU read-side critical sections are delimited by :
187  *  - rcu_read_lock_sched() and  rcu_read_unlock_sched(),
188  *  OR
189  *  anything that disables preemption.
190  *  These may be nested.
191  *
192  * See the description of call_rcu() for more detailed information on
193  * memory ordering guarantees.
194  */
195 void call_rcu_sched(struct rcu_head *head,
196                     void (*func)(struct rcu_head *rcu));
197 
198 void synchronize_sched(void);
199 
200 #ifdef CONFIG_PREEMPT_RCU
201 
202 void __rcu_read_lock(void);
203 void __rcu_read_unlock(void);
204 void rcu_read_unlock_special(struct task_struct *t);
205 void synchronize_rcu(void);
206 
207 /*
208  * Defined as a macro as it is a very low level header included from
209  * areas that don't even know about current.  This gives the rcu_read_lock()
210  * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
211  * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
212  */
213 #define rcu_preempt_depth() (current->rcu_read_lock_nesting)
214 
215 #else /* #ifdef CONFIG_PREEMPT_RCU */
216 
217 static inline void __rcu_read_lock(void)
218 {
219         preempt_disable();
220 }
221 
222 static inline void __rcu_read_unlock(void)
223 {
224         preempt_enable();
225 }
226 
227 static inline void synchronize_rcu(void)
228 {
229         synchronize_sched();
230 }
231 
232 static inline int rcu_preempt_depth(void)
233 {
234         return 0;
235 }
236 
237 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
238 
239 /* Internal to kernel */
240 void rcu_init(void);
241 void rcu_sched_qs(int cpu);
242 void rcu_bh_qs(int cpu);
243 void rcu_check_callbacks(int cpu, int user);
244 struct notifier_block;
245 void rcu_idle_enter(void);
246 void rcu_idle_exit(void);
247 void rcu_irq_enter(void);
248 void rcu_irq_exit(void);
249 
250 #ifdef CONFIG_RCU_STALL_COMMON
251 void rcu_sysrq_start(void);
252 void rcu_sysrq_end(void);
253 #else /* #ifdef CONFIG_RCU_STALL_COMMON */
254 static inline void rcu_sysrq_start(void)
255 {
256 }
257 static inline void rcu_sysrq_end(void)
258 {
259 }
260 #endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
261 
262 #ifdef CONFIG_RCU_USER_QS
263 void rcu_user_enter(void);
264 void rcu_user_exit(void);
265 #else
266 static inline void rcu_user_enter(void) { }
267 static inline void rcu_user_exit(void) { }
268 static inline void rcu_user_hooks_switch(struct task_struct *prev,
269                                          struct task_struct *next) { }
270 #endif /* CONFIG_RCU_USER_QS */
271 
272 /**
273  * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
274  * @a: Code that RCU needs to pay attention to.
275  *
276  * RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden
277  * in the inner idle loop, that is, between the rcu_idle_enter() and
278  * the rcu_idle_exit() -- RCU will happily ignore any such read-side
279  * critical sections.  However, things like powertop need tracepoints
280  * in the inner idle loop.
281  *
282  * This macro provides the way out:  RCU_NONIDLE(do_something_with_RCU())
283  * will tell RCU that it needs to pay attending, invoke its argument
284  * (in this example, a call to the do_something_with_RCU() function),
285  * and then tell RCU to go back to ignoring this CPU.  It is permissible
286  * to nest RCU_NONIDLE() wrappers, but the nesting level is currently
287  * quite limited.  If deeper nesting is required, it will be necessary
288  * to adjust DYNTICK_TASK_NESTING_VALUE accordingly.
289  */
290 #define RCU_NONIDLE(a) \
291         do { \
292                 rcu_irq_enter(); \
293                 do { a; } while (0); \
294                 rcu_irq_exit(); \
295         } while (0)
296 
297 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP)
298 bool __rcu_is_watching(void);
299 #endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP) */
300 
301 /*
302  * Infrastructure to implement the synchronize_() primitives in
303  * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
304  */
305 
306 typedef void call_rcu_func_t(struct rcu_head *head,
307                              void (*func)(struct rcu_head *head));
308 void wait_rcu_gp(call_rcu_func_t crf);
309 
310 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
311 #include <linux/rcutree.h>
312 #elif defined(CONFIG_TINY_RCU)
313 #include <linux/rcutiny.h>
314 #else
315 #error "Unknown RCU implementation specified to kernel configuration"
316 #endif
317 
318 /*
319  * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic
320  * initialization and destruction of rcu_head on the stack. rcu_head structures
321  * allocated dynamically in the heap or defined statically don't need any
322  * initialization.
323  */
324 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
325 void init_rcu_head(struct rcu_head *head);
326 void destroy_rcu_head(struct rcu_head *head);
327 void init_rcu_head_on_stack(struct rcu_head *head);
328 void destroy_rcu_head_on_stack(struct rcu_head *head);
329 #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
330 static inline void init_rcu_head(struct rcu_head *head)
331 {
332 }
333 
334 static inline void destroy_rcu_head(struct rcu_head *head)
335 {
336 }
337 
338 static inline void init_rcu_head_on_stack(struct rcu_head *head)
339 {
340 }
341 
342 static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
343 {
344 }
345 #endif  /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
346 
347 #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
348 bool rcu_lockdep_current_cpu_online(void);
349 #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
350 static inline bool rcu_lockdep_current_cpu_online(void)
351 {
352         return 1;
353 }
354 #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
355 
356 #ifdef CONFIG_DEBUG_LOCK_ALLOC
357 
358 static inline void rcu_lock_acquire(struct lockdep_map *map)
359 {
360         lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
361 }
362 
363 static inline void rcu_lock_release(struct lockdep_map *map)
364 {
365         lock_release(map, 1, _THIS_IP_);
366 }
367 
368 extern struct lockdep_map rcu_lock_map;
369 extern struct lockdep_map rcu_bh_lock_map;
370 extern struct lockdep_map rcu_sched_lock_map;
371 extern struct lockdep_map rcu_callback_map;
372 int debug_lockdep_rcu_enabled(void);
373 
374 /**
375  * rcu_read_lock_held() - might we be in RCU read-side critical section?
376  *
377  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
378  * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
379  * this assumes we are in an RCU read-side critical section unless it can
380  * prove otherwise.  This is useful for debug checks in functions that
381  * require that they be called within an RCU read-side critical section.
382  *
383  * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
384  * and while lockdep is disabled.
385  *
386  * Note that rcu_read_lock() and the matching rcu_read_unlock() must
387  * occur in the same context, for example, it is illegal to invoke
388  * rcu_read_unlock() in process context if the matching rcu_read_lock()
389  * was invoked from within an irq handler.
390  *
391  * Note that rcu_read_lock() is disallowed if the CPU is either idle or
392  * offline from an RCU perspective, so check for those as well.
393  */
394 static inline int rcu_read_lock_held(void)
395 {
396         if (!debug_lockdep_rcu_enabled())
397                 return 1;
398         if (!rcu_is_watching())
399                 return 0;
400         if (!rcu_lockdep_current_cpu_online())
401                 return 0;
402         return lock_is_held(&rcu_lock_map);
403 }
404 
405 /*
406  * rcu_read_lock_bh_held() is defined out of line to avoid #include-file
407  * hell.
408  */
409 int rcu_read_lock_bh_held(void);
410 
411 /**
412  * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
413  *
414  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
415  * RCU-sched read-side critical section.  In absence of
416  * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
417  * critical section unless it can prove otherwise.  Note that disabling
418  * of preemption (including disabling irqs) counts as an RCU-sched
419  * read-side critical section.  This is useful for debug checks in functions
420  * that required that they be called within an RCU-sched read-side
421  * critical section.
422  *
423  * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
424  * and while lockdep is disabled.
425  *
426  * Note that if the CPU is in the idle loop from an RCU point of
427  * view (ie: that we are in the section between rcu_idle_enter() and
428  * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
429  * did an rcu_read_lock().  The reason for this is that RCU ignores CPUs
430  * that are in such a section, considering these as in extended quiescent
431  * state, so such a CPU is effectively never in an RCU read-side critical
432  * section regardless of what RCU primitives it invokes.  This state of
433  * affairs is required --- we need to keep an RCU-free window in idle
434  * where the CPU may possibly enter into low power mode. This way we can
435  * notice an extended quiescent state to other CPUs that started a grace
436  * period. Otherwise we would delay any grace period as long as we run in
437  * the idle task.
438  *
439  * Similarly, we avoid claiming an SRCU read lock held if the current
440  * CPU is offline.
441  */
442 #ifdef CONFIG_PREEMPT_COUNT
443 static inline int rcu_read_lock_sched_held(void)
444 {
445         int lockdep_opinion = 0;
446 
447         if (!debug_lockdep_rcu_enabled())
448                 return 1;
449         if (!rcu_is_watching())
450                 return 0;
451         if (!rcu_lockdep_current_cpu_online())
452                 return 0;
453         if (debug_locks)
454                 lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
455         return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
456 }
457 #else /* #ifdef CONFIG_PREEMPT_COUNT */
458 static inline int rcu_read_lock_sched_held(void)
459 {
460         return 1;
461 }
462 #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
463 
464 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
465 
466 # define rcu_lock_acquire(a)            do { } while (0)
467 # define rcu_lock_release(a)            do { } while (0)
468 
469 static inline int rcu_read_lock_held(void)
470 {
471         return 1;
472 }
473 
474 static inline int rcu_read_lock_bh_held(void)
475 {
476         return 1;
477 }
478 
479 #ifdef CONFIG_PREEMPT_COUNT
480 static inline int rcu_read_lock_sched_held(void)
481 {
482         return preempt_count() != 0 || irqs_disabled();
483 }
484 #else /* #ifdef CONFIG_PREEMPT_COUNT */
485 static inline int rcu_read_lock_sched_held(void)
486 {
487         return 1;
488 }
489 #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
490 
491 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
492 
493 #ifdef CONFIG_PROVE_RCU
494 
495 /**
496  * rcu_lockdep_assert - emit lockdep splat if specified condition not met
497  * @c: condition to check
498  * @s: informative message
499  */
500 #define rcu_lockdep_assert(c, s)                                        \
501         do {                                                            \
502                 static bool __section(.data.unlikely) __warned;         \
503                 if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
504                         __warned = true;                                \
505                         lockdep_rcu_suspicious(__FILE__, __LINE__, s);  \
506                 }                                                       \
507         } while (0)
508 
509 #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
510 static inline void rcu_preempt_sleep_check(void)
511 {
512         rcu_lockdep_assert(!lock_is_held(&rcu_lock_map),
513                            "Illegal context switch in RCU read-side critical section");
514 }
515 #else /* #ifdef CONFIG_PROVE_RCU */
516 static inline void rcu_preempt_sleep_check(void)
517 {
518 }
519 #endif /* #else #ifdef CONFIG_PROVE_RCU */
520 
521 #define rcu_sleep_check()                                               \
522         do {                                                            \
523                 rcu_preempt_sleep_check();                              \
524                 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map),     \
525                                    "Illegal context switch in RCU-bh read-side critical section"); \
526                 rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map),  \
527                                    "Illegal context switch in RCU-sched read-side critical section"); \
528         } while (0)
529 
530 #else /* #ifdef CONFIG_PROVE_RCU */
531 
532 #define rcu_lockdep_assert(c, s) do { } while (0)
533 #define rcu_sleep_check() do { } while (0)
534 
535 #endif /* #else #ifdef CONFIG_PROVE_RCU */
536 
537 /*
538  * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
539  * and rcu_assign_pointer().  Some of these could be folded into their
540  * callers, but they are left separate in order to ease introduction of
541  * multiple flavors of pointers to match the multiple flavors of RCU
542  * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in
543  * the future.
544  */
545 
546 #ifdef __CHECKER__
547 #define rcu_dereference_sparse(p, space) \
548         ((void)(((typeof(*p) space *)p) == p))
549 #else /* #ifdef __CHECKER__ */
550 #define rcu_dereference_sparse(p, space)
551 #endif /* #else #ifdef __CHECKER__ */
552 
553 #define __rcu_access_pointer(p, space) \
554 ({ \
555         typeof(*p) *_________p1 = (typeof(*p) *__force)ACCESS_ONCE(p); \
556         rcu_dereference_sparse(p, space); \
557         ((typeof(*p) __force __kernel *)(_________p1)); \
558 })
559 #define __rcu_dereference_check(p, c, space) \
560 ({ \
561         typeof(*p) *_________p1 = (typeof(*p) *__force)ACCESS_ONCE(p); \
562         rcu_lockdep_assert(c, "suspicious rcu_dereference_check() usage"); \
563         rcu_dereference_sparse(p, space); \
564         smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
565         ((typeof(*p) __force __kernel *)(_________p1)); \
566 })
567 #define __rcu_dereference_protected(p, c, space) \
568 ({ \
569         rcu_lockdep_assert(c, "suspicious rcu_dereference_protected() usage"); \
570         rcu_dereference_sparse(p, space); \
571         ((typeof(*p) __force __kernel *)(p)); \
572 })
573 
574 #define __rcu_access_index(p, space) \
575 ({ \
576         typeof(p) _________p1 = ACCESS_ONCE(p); \
577         rcu_dereference_sparse(p, space); \
578         (_________p1); \
579 })
580 #define __rcu_dereference_index_check(p, c) \
581 ({ \
582         typeof(p) _________p1 = ACCESS_ONCE(p); \
583         rcu_lockdep_assert(c, \
584                            "suspicious rcu_dereference_index_check() usage"); \
585         smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
586         (_________p1); \
587 })
588 
589 /**
590  * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
591  * @v: The value to statically initialize with.
592  */
593 #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
594 
595 /**
596  * rcu_assign_pointer() - assign to RCU-protected pointer
597  * @p: pointer to assign to
598  * @v: value to assign (publish)
599  *
600  * Assigns the specified value to the specified RCU-protected
601  * pointer, ensuring that any concurrent RCU readers will see
602  * any prior initialization.
603  *
604  * Inserts memory barriers on architectures that require them
605  * (which is most of them), and also prevents the compiler from
606  * reordering the code that initializes the structure after the pointer
607  * assignment.  More importantly, this call documents which pointers
608  * will be dereferenced by RCU read-side code.
609  *
610  * In some special cases, you may use RCU_INIT_POINTER() instead
611  * of rcu_assign_pointer().  RCU_INIT_POINTER() is a bit faster due
612  * to the fact that it does not constrain either the CPU or the compiler.
613  * That said, using RCU_INIT_POINTER() when you should have used
614  * rcu_assign_pointer() is a very bad thing that results in
615  * impossible-to-diagnose memory corruption.  So please be careful.
616  * See the RCU_INIT_POINTER() comment header for details.
617  *
618  * Note that rcu_assign_pointer() evaluates each of its arguments only
619  * once, appearances notwithstanding.  One of the "extra" evaluations
620  * is in typeof() and the other visible only to sparse (__CHECKER__),
621  * neither of which actually execute the argument.  As with most cpp
622  * macros, this execute-arguments-only-once property is important, so
623  * please be careful when making changes to rcu_assign_pointer() and the
624  * other macros that it invokes.
625  */
626 #define rcu_assign_pointer(p, v) smp_store_release(&p, RCU_INITIALIZER(v))
627 
628 /**
629  * rcu_access_pointer() - fetch RCU pointer with no dereferencing
630  * @p: The pointer to read
631  *
632  * Return the value of the specified RCU-protected pointer, but omit the
633  * smp_read_barrier_depends() and keep the ACCESS_ONCE().  This is useful
634  * when the value of this pointer is accessed, but the pointer is not
635  * dereferenced, for example, when testing an RCU-protected pointer against
636  * NULL.  Although rcu_access_pointer() may also be used in cases where
637  * update-side locks prevent the value of the pointer from changing, you
638  * should instead use rcu_dereference_protected() for this use case.
639  *
640  * It is also permissible to use rcu_access_pointer() when read-side
641  * access to the pointer was removed at least one grace period ago, as
642  * is the case in the context of the RCU callback that is freeing up
643  * the data, or after a synchronize_rcu() returns.  This can be useful
644  * when tearing down multi-linked structures after a grace period
645  * has elapsed.
646  */
647 #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
648 
649 /**
650  * rcu_dereference_check() - rcu_dereference with debug checking
651  * @p: The pointer to read, prior to dereferencing
652  * @c: The conditions under which the dereference will take place
653  *
654  * Do an rcu_dereference(), but check that the conditions under which the
655  * dereference will take place are correct.  Typically the conditions
656  * indicate the various locking conditions that should be held at that
657  * point.  The check should return true if the conditions are satisfied.
658  * An implicit check for being in an RCU read-side critical section
659  * (rcu_read_lock()) is included.
660  *
661  * For example:
662  *
663  *      bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
664  *
665  * could be used to indicate to lockdep that foo->bar may only be dereferenced
666  * if either rcu_read_lock() is held, or that the lock required to replace
667  * the bar struct at foo->bar is held.
668  *
669  * Note that the list of conditions may also include indications of when a lock
670  * need not be held, for example during initialisation or destruction of the
671  * target struct:
672  *
673  *      bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
674  *                                            atomic_read(&foo->usage) == 0);
675  *
676  * Inserts memory barriers on architectures that require them
677  * (currently only the Alpha), prevents the compiler from refetching
678  * (and from merging fetches), and, more importantly, documents exactly
679  * which pointers are protected by RCU and checks that the pointer is
680  * annotated as __rcu.
681  */
682 #define rcu_dereference_check(p, c) \
683         __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)
684 
685 /**
686  * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
687  * @p: The pointer to read, prior to dereferencing
688  * @c: The conditions under which the dereference will take place
689  *
690  * This is the RCU-bh counterpart to rcu_dereference_check().
691  */
692 #define rcu_dereference_bh_check(p, c) \
693         __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu)
694 
695 /**
696  * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
697  * @p: The pointer to read, prior to dereferencing
698  * @c: The conditions under which the dereference will take place
699  *
700  * This is the RCU-sched counterpart to rcu_dereference_check().
701  */
702 #define rcu_dereference_sched_check(p, c) \
703         __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \
704                                 __rcu)
705 
706 #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/
707 
708 /*
709  * The tracing infrastructure traces RCU (we want that), but unfortunately
710  * some of the RCU checks causes tracing to lock up the system.
711  *
712  * The tracing version of rcu_dereference_raw() must not call
713  * rcu_read_lock_held().
714  */
715 #define rcu_dereference_raw_notrace(p) __rcu_dereference_check((p), 1, __rcu)
716 
717 /**
718  * rcu_access_index() - fetch RCU index with no dereferencing
719  * @p: The index to read
720  *
721  * Return the value of the specified RCU-protected index, but omit the
722  * smp_read_barrier_depends() and keep the ACCESS_ONCE().  This is useful
723  * when the value of this index is accessed, but the index is not
724  * dereferenced, for example, when testing an RCU-protected index against
725  * -1.  Although rcu_access_index() may also be used in cases where
726  * update-side locks prevent the value of the index from changing, you
727  * should instead use rcu_dereference_index_protected() for this use case.
728  */
729 #define rcu_access_index(p) __rcu_access_index((p), __rcu)
730 
731 /**
732  * rcu_dereference_index_check() - rcu_dereference for indices with debug checking
733  * @p: The pointer to read, prior to dereferencing
734  * @c: The conditions under which the dereference will take place
735  *
736  * Similar to rcu_dereference_check(), but omits the sparse checking.
737  * This allows rcu_dereference_index_check() to be used on integers,
738  * which can then be used as array indices.  Attempting to use
739  * rcu_dereference_check() on an integer will give compiler warnings
740  * because the sparse address-space mechanism relies on dereferencing
741  * the RCU-protected pointer.  Dereferencing integers is not something
742  * that even gcc will put up with.
743  *
744  * Note that this function does not implicitly check for RCU read-side
745  * critical sections.  If this function gains lots of uses, it might
746  * make sense to provide versions for each flavor of RCU, but it does
747  * not make sense as of early 2010.
748  */
749 #define rcu_dereference_index_check(p, c) \
750         __rcu_dereference_index_check((p), (c))
751 
752 /**
753  * rcu_dereference_protected() - fetch RCU pointer when updates prevented
754  * @p: The pointer to read, prior to dereferencing
755  * @c: The conditions under which the dereference will take place
756  *
757  * Return the value of the specified RCU-protected pointer, but omit
758  * both the smp_read_barrier_depends() and the ACCESS_ONCE().  This
759  * is useful in cases where update-side locks prevent the value of the
760  * pointer from changing.  Please note that this primitive does -not-
761  * prevent the compiler from repeating this reference or combining it
762  * with other references, so it should not be used without protection
763  * of appropriate locks.
764  *
765  * This function is only for update-side use.  Using this function
766  * when protected only by rcu_read_lock() will result in infrequent
767  * but very ugly failures.
768  */
769 #define rcu_dereference_protected(p, c) \
770         __rcu_dereference_protected((p), (c), __rcu)
771 
772 
773 /**
774  * rcu_dereference() - fetch RCU-protected pointer for dereferencing
775  * @p: The pointer to read, prior to dereferencing
776  *
777  * This is a simple wrapper around rcu_dereference_check().
778  */
779 #define rcu_dereference(p) rcu_dereference_check(p, 0)
780 
781 /**
782  * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
783  * @p: The pointer to read, prior to dereferencing
784  *
785  * Makes rcu_dereference_check() do the dirty work.
786  */
787 #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
788 
789 /**
790  * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
791  * @p: The pointer to read, prior to dereferencing
792  *
793  * Makes rcu_dereference_check() do the dirty work.
794  */
795 #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
796 
797 /**
798  * rcu_read_lock() - mark the beginning of an RCU read-side critical section
799  *
800  * When synchronize_rcu() is invoked on one CPU while other CPUs
801  * are within RCU read-side critical sections, then the
802  * synchronize_rcu() is guaranteed to block until after all the other
803  * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
804  * on one CPU while other CPUs are within RCU read-side critical
805  * sections, invocation of the corresponding RCU callback is deferred
806  * until after the all the other CPUs exit their critical sections.
807  *
808  * Note, however, that RCU callbacks are permitted to run concurrently
809  * with new RCU read-side critical sections.  One way that this can happen
810  * is via the following sequence of events: (1) CPU 0 enters an RCU
811  * read-side critical section, (2) CPU 1 invokes call_rcu() to register
812  * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
813  * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
814  * callback is invoked.  This is legal, because the RCU read-side critical
815  * section that was running concurrently with the call_rcu() (and which
816  * therefore might be referencing something that the corresponding RCU
817  * callback would free up) has completed before the corresponding
818  * RCU callback is invoked.
819  *
820  * RCU read-side critical sections may be nested.  Any deferred actions
821  * will be deferred until the outermost RCU read-side critical section
822  * completes.
823  *
824  * You can avoid reading and understanding the next paragraph by
825  * following this rule: don't put anything in an rcu_read_lock() RCU
826  * read-side critical section that would block in a !PREEMPT kernel.
827  * But if you want the full story, read on!
828  *
829  * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it
830  * is illegal to block while in an RCU read-side critical section.  In
831  * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU)
832  * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may
833  * be preempted, but explicit blocking is illegal.  Finally, in preemptible
834  * RCU implementations in real-time (with -rt patchset) kernel builds,
835  * RCU read-side critical sections may be preempted and they may also
836  * block, but only when acquiring spinlocks that are subject to priority
837  * inheritance.
838  */
839 static inline void rcu_read_lock(void)
840 {
841         __rcu_read_lock();
842         __acquire(RCU);
843         rcu_lock_acquire(&rcu_lock_map);
844         rcu_lockdep_assert(rcu_is_watching(),
845                            "rcu_read_lock() used illegally while idle");
846 }
847 
848 /*
849  * So where is rcu_write_lock()?  It does not exist, as there is no
850  * way for writers to lock out RCU readers.  This is a feature, not
851  * a bug -- this property is what provides RCU's performance benefits.
852  * Of course, writers must coordinate with each other.  The normal
853  * spinlock primitives work well for this, but any other technique may be
854  * used as well.  RCU does not care how the writers keep out of each
855  * others' way, as long as they do so.
856  */
857 
858 /**
859  * rcu_read_unlock() - marks the end of an RCU read-side critical section.
860  *
861  * See rcu_read_lock() for more information.
862  */
863 static inline void rcu_read_unlock(void)
864 {
865         rcu_lockdep_assert(rcu_is_watching(),
866                            "rcu_read_unlock() used illegally while idle");
867         rcu_lock_release(&rcu_lock_map);
868         __release(RCU);
869         __rcu_read_unlock();
870 }
871 
872 /**
873  * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
874  *
875  * This is equivalent of rcu_read_lock(), but to be used when updates
876  * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since
877  * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a
878  * softirq handler to be a quiescent state, a process in RCU read-side
879  * critical section must be protected by disabling softirqs. Read-side
880  * critical sections in interrupt context can use just rcu_read_lock(),
881  * though this should at least be commented to avoid confusing people
882  * reading the code.
883  *
884  * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
885  * must occur in the same context, for example, it is illegal to invoke
886  * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
887  * was invoked from some other task.
888  */
889 static inline void rcu_read_lock_bh(void)
890 {
891         local_bh_disable();
892         __acquire(RCU_BH);
893         rcu_lock_acquire(&rcu_bh_lock_map);
894         rcu_lockdep_assert(rcu_is_watching(),
895                            "rcu_read_lock_bh() used illegally while idle");
896 }
897 
898 /*
899  * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
900  *
901  * See rcu_read_lock_bh() for more information.
902  */
903 static inline void rcu_read_unlock_bh(void)
904 {
905         rcu_lockdep_assert(rcu_is_watching(),
906                            "rcu_read_unlock_bh() used illegally while idle");
907         rcu_lock_release(&rcu_bh_lock_map);
908         __release(RCU_BH);
909         local_bh_enable();
910 }
911 
912 /**
913  * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
914  *
915  * This is equivalent of rcu_read_lock(), but to be used when updates
916  * are being done using call_rcu_sched() or synchronize_rcu_sched().
917  * Read-side critical sections can also be introduced by anything that
918  * disables preemption, including local_irq_disable() and friends.
919  *
920  * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
921  * must occur in the same context, for example, it is illegal to invoke
922  * rcu_read_unlock_sched() from process context if the matching
923  * rcu_read_lock_sched() was invoked from an NMI handler.
924  */
925 static inline void rcu_read_lock_sched(void)
926 {
927         preempt_disable();
928         __acquire(RCU_SCHED);
929         rcu_lock_acquire(&rcu_sched_lock_map);
930         rcu_lockdep_assert(rcu_is_watching(),
931                            "rcu_read_lock_sched() used illegally while idle");
932 }
933 
934 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
935 static inline notrace void rcu_read_lock_sched_notrace(void)
936 {
937         preempt_disable_notrace();
938         __acquire(RCU_SCHED);
939 }
940 
941 /*
942  * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
943  *
944  * See rcu_read_lock_sched for more information.
945  */
946 static inline void rcu_read_unlock_sched(void)
947 {
948         rcu_lockdep_assert(rcu_is_watching(),
949                            "rcu_read_unlock_sched() used illegally while idle");
950         rcu_lock_release(&rcu_sched_lock_map);
951         __release(RCU_SCHED);
952         preempt_enable();
953 }
954 
955 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
956 static inline notrace void rcu_read_unlock_sched_notrace(void)
957 {
958         __release(RCU_SCHED);
959         preempt_enable_notrace();
960 }
961 
962 /**
963  * RCU_INIT_POINTER() - initialize an RCU protected pointer
964  *
965  * Initialize an RCU-protected pointer in special cases where readers
966  * do not need ordering constraints on the CPU or the compiler.  These
967  * special cases are:
968  *
969  * 1.   This use of RCU_INIT_POINTER() is NULLing out the pointer -or-
970  * 2.   The caller has taken whatever steps are required to prevent
971  *      RCU readers from concurrently accessing this pointer -or-
972  * 3.   The referenced data structure has already been exposed to
973  *      readers either at compile time or via rcu_assign_pointer() -and-
974  *      a.      You have not made -any- reader-visible changes to
975  *              this structure since then -or-
976  *      b.      It is OK for readers accessing this structure from its
977  *              new location to see the old state of the structure.  (For
978  *              example, the changes were to statistical counters or to
979  *              other state where exact synchronization is not required.)
980  *
981  * Failure to follow these rules governing use of RCU_INIT_POINTER() will
982  * result in impossible-to-diagnose memory corruption.  As in the structures
983  * will look OK in crash dumps, but any concurrent RCU readers might
984  * see pre-initialized values of the referenced data structure.  So
985  * please be very careful how you use RCU_INIT_POINTER()!!!
986  *
987  * If you are creating an RCU-protected linked structure that is accessed
988  * by a single external-to-structure RCU-protected pointer, then you may
989  * use RCU_INIT_POINTER() to initialize the internal RCU-protected
990  * pointers, but you must use rcu_assign_pointer() to initialize the
991  * external-to-structure pointer -after- you have completely initialized
992  * the reader-accessible portions of the linked structure.
993  *
994  * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
995  * ordering guarantees for either the CPU or the compiler.
996  */
997 #define RCU_INIT_POINTER(p, v) \
998         do { \
999                 p = RCU_INITIALIZER(v); \
1000         } while (0)
1001 
1002 /**
1003  * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
1004  *
1005  * GCC-style initialization for an RCU-protected pointer in a structure field.
1006  */
1007 #define RCU_POINTER_INITIALIZER(p, v) \
1008                 .p = RCU_INITIALIZER(v)
1009 
1010 /*
1011  * Does the specified offset indicate that the corresponding rcu_head
1012  * structure can be handled by kfree_rcu()?
1013  */
1014 #define __is_kfree_rcu_offset(offset) ((offset) < 4096)
1015 
1016 /*
1017  * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain.
1018  */
1019 #define __kfree_rcu(head, offset) \
1020         do { \
1021                 BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \
1022                 kfree_call_rcu(head, (void (*)(struct rcu_head *))(unsigned long)(offset)); \
1023         } while (0)
1024 
1025 /**
1026  * kfree_rcu() - kfree an object after a grace period.
1027  * @ptr:        pointer to kfree
1028  * @rcu_head:   the name of the struct rcu_head within the type of @ptr.
1029  *
1030  * Many rcu callbacks functions just call kfree() on the base structure.
1031  * These functions are trivial, but their size adds up, and furthermore
1032  * when they are used in a kernel module, that module must invoke the
1033  * high-latency rcu_barrier() function at module-unload time.
1034  *
1035  * The kfree_rcu() function handles this issue.  Rather than encoding a
1036  * function address in the embedded rcu_head structure, kfree_rcu() instead
1037  * encodes the offset of the rcu_head structure within the base structure.
1038  * Because the functions are not allowed in the low-order 4096 bytes of
1039  * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
1040  * If the offset is larger than 4095 bytes, a compile-time error will
1041  * be generated in __kfree_rcu().  If this error is triggered, you can
1042  * either fall back to use of call_rcu() or rearrange the structure to
1043  * position the rcu_head structure into the first 4096 bytes.
1044  *
1045  * Note that the allowable offset might decrease in the future, for example,
1046  * to allow something like kmem_cache_free_rcu().
1047  *
1048  * The BUILD_BUG_ON check must not involve any function calls, hence the
1049  * checks are done in macros here.
1050  */
1051 #define kfree_rcu(ptr, rcu_head)                                        \
1052         __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
1053 
1054 #if defined(CONFIG_TINY_RCU) || defined(CONFIG_RCU_NOCB_CPU_ALL)
1055 static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
1056 {
1057         *delta_jiffies = ULONG_MAX;
1058         return 0;
1059 }
1060 #endif /* #if defined(CONFIG_TINY_RCU) || defined(CONFIG_RCU_NOCB_CPU_ALL) */
1061 
1062 #if defined(CONFIG_RCU_NOCB_CPU_ALL)
1063 static inline bool rcu_is_nocb_cpu(int cpu) { return true; }
1064 #elif defined(CONFIG_RCU_NOCB_CPU)
1065 bool rcu_is_nocb_cpu(int cpu);
1066 #else
1067 static inline bool rcu_is_nocb_cpu(int cpu) { return false; }
1068 #endif
1069 
1070 
1071 /* Only for use by adaptive-ticks code. */
1072 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
1073 bool rcu_sys_is_idle(void);
1074 void rcu_sysidle_force_exit(void);
1075 #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
1076 
1077 static inline bool rcu_sys_is_idle(void)
1078 {
1079         return false;
1080 }
1081 
1082 static inline void rcu_sysidle_force_exit(void)
1083 {
1084 }
1085 
1086 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
1087 
1088 
1089 #endif /* __LINUX_RCUPDATE_H */
1090 

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