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TOMOYO Linux Cross Reference
Linux/include/linux/rcupdate.h

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

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