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Linux/include/linux/rcupdate.h

  1 /*
  2  * Read-Copy Update mechanism for mutual exclusion
  3  *
  4  * This program is free software; you can redistribute it and/or modify
  5  * it under the terms of the GNU General Public License as published by
  6  * the Free Software Foundation; either version 2 of the License, or
  7  * (at your option) any later version.
  8  *
  9  * This program is distributed in the hope that it will be useful,
 10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
 11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 12  * GNU General Public License for more details.
 13  *
 14  * You should have received a copy of the GNU General Public License
 15  * along with this program; if not, you can access it online at
 16  * http://www.gnu.org/licenses/gpl-2.0.html.
 17  *
 18  * Copyright IBM Corporation, 2001
 19  *
 20  * Author: Dipankar Sarma <dipankar@in.ibm.com>
 21  *
 22  * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
 23  * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
 24  * Papers:
 25  * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
 26  * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
 27  *
 28  * For detailed explanation of Read-Copy Update mechanism see -
 29  *              http://lse.sourceforge.net/locking/rcupdate.html
 30  *
 31  */
 32 
 33 #ifndef __LINUX_RCUPDATE_H
 34 #define __LINUX_RCUPDATE_H
 35 
 36 #include <linux/types.h>
 37 #include <linux/cache.h>
 38 #include <linux/spinlock.h>
 39 #include <linux/threads.h>
 40 #include <linux/cpumask.h>
 41 #include <linux/seqlock.h>
 42 #include <linux/lockdep.h>
 43 #include <linux/completion.h>
 44 #include <linux/debugobjects.h>
 45 #include <linux/bug.h>
 46 #include <linux/compiler.h>
 47 #include <asm/barrier.h>
 48 
 49 extern int rcu_expedited; /* for sysctl */
 50 
 51 #ifdef CONFIG_TINY_RCU
 52 /* Tiny RCU doesn't expedite, as its purpose in life is instead to be tiny. */
 53 static inline bool rcu_gp_is_expedited(void)  /* Internal RCU use. */
 54 {
 55         return false;
 56 }
 57 
 58 static inline void rcu_expedite_gp(void)
 59 {
 60 }
 61 
 62 static inline void rcu_unexpedite_gp(void)
 63 {
 64 }
 65 #else /* #ifdef CONFIG_TINY_RCU */
 66 bool rcu_gp_is_expedited(void);  /* Internal RCU use. */
 67 void rcu_expedite_gp(void);
 68 void rcu_unexpedite_gp(void);
 69 #endif /* #else #ifdef CONFIG_TINY_RCU */
 70 
 71 enum rcutorture_type {
 72         RCU_FLAVOR,
 73         RCU_BH_FLAVOR,
 74         RCU_SCHED_FLAVOR,
 75         RCU_TASKS_FLAVOR,
 76         SRCU_FLAVOR,
 77         INVALID_RCU_FLAVOR
 78 };
 79 
 80 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
 81 void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
 82                             unsigned long *gpnum, unsigned long *completed);
 83 void rcutorture_record_test_transition(void);
 84 void rcutorture_record_progress(unsigned long vernum);
 85 void do_trace_rcu_torture_read(const char *rcutorturename,
 86                                struct rcu_head *rhp,
 87                                unsigned long secs,
 88                                unsigned long c_old,
 89                                unsigned long c);
 90 #else
 91 static inline void rcutorture_get_gp_data(enum rcutorture_type test_type,
 92                                           int *flags,
 93                                           unsigned long *gpnum,
 94                                           unsigned long *completed)
 95 {
 96         *flags = 0;
 97         *gpnum = 0;
 98         *completed = 0;
 99 }
100 static inline void rcutorture_record_test_transition(void)
101 {
102 }
103 static inline void rcutorture_record_progress(unsigned long vernum)
104 {
105 }
106 #ifdef CONFIG_RCU_TRACE
107 void do_trace_rcu_torture_read(const char *rcutorturename,
108                                struct rcu_head *rhp,
109                                unsigned long secs,
110                                unsigned long c_old,
111                                unsigned long c);
112 #else
113 #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
114         do { } while (0)
115 #endif
116 #endif
117 
118 #define UINT_CMP_GE(a, b)       (UINT_MAX / 2 >= (a) - (b))
119 #define UINT_CMP_LT(a, b)       (UINT_MAX / 2 < (a) - (b))
120 #define ULONG_CMP_GE(a, b)      (ULONG_MAX / 2 >= (a) - (b))
121 #define ULONG_CMP_LT(a, b)      (ULONG_MAX / 2 < (a) - (b))
122 #define ulong2long(a)           (*(long *)(&(a)))
123 
124 /* Exported common interfaces */
125 
126 #ifdef CONFIG_PREEMPT_RCU
127 
128 /**
129  * call_rcu() - Queue an RCU callback for invocation after a grace period.
130  * @head: structure to be used for queueing the RCU updates.
131  * @func: actual callback function to be invoked after the grace period
132  *
133  * The callback function will be invoked some time after a full grace
134  * period elapses, in other words after all pre-existing RCU read-side
135  * critical sections have completed.  However, the callback function
136  * might well execute concurrently with RCU read-side critical sections
137  * that started after call_rcu() was invoked.  RCU read-side critical
138  * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
139  * and may be nested.
140  *
141  * Note that all CPUs must agree that the grace period extended beyond
142  * all pre-existing RCU read-side critical section.  On systems with more
143  * than one CPU, this means that when "func()" is invoked, each CPU is
144  * guaranteed to have executed a full memory barrier since the end of its
145  * last RCU read-side critical section whose beginning preceded the call
146  * to call_rcu().  It also means that each CPU executing an RCU read-side
147  * critical section that continues beyond the start of "func()" must have
148  * executed a memory barrier after the call_rcu() but before the beginning
149  * of that RCU read-side critical section.  Note that these guarantees
150  * include CPUs that are offline, idle, or executing in user mode, as
151  * well as CPUs that are executing in the kernel.
152  *
153  * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
154  * resulting RCU callback function "func()", then both CPU A and CPU B are
155  * guaranteed to execute a full memory barrier during the time interval
156  * between the call to call_rcu() and the invocation of "func()" -- even
157  * if CPU A and CPU B are the same CPU (but again only if the system has
158  * more than one CPU).
159  */
160 void call_rcu(struct rcu_head *head,
161               void (*func)(struct rcu_head *head));
162 
163 #else /* #ifdef CONFIG_PREEMPT_RCU */
164 
165 /* In classic RCU, call_rcu() is just call_rcu_sched(). */
166 #define call_rcu        call_rcu_sched
167 
168 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
169 
170 /**
171  * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
172  * @head: structure to be used for queueing the RCU updates.
173  * @func: actual callback function to be invoked after the grace period
174  *
175  * The callback function will be invoked some time after a full grace
176  * period elapses, in other words after all currently executing RCU
177  * read-side critical sections have completed. call_rcu_bh() assumes
178  * that the read-side critical sections end on completion of a softirq
179  * handler. This means that read-side critical sections in process
180  * context must not be interrupted by softirqs. This interface is to be
181  * used when most of the read-side critical sections are in softirq context.
182  * RCU read-side critical sections are delimited by :
183  *  - rcu_read_lock() and  rcu_read_unlock(), if in interrupt context.
184  *  OR
185  *  - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
186  *  These may be nested.
187  *
188  * See the description of call_rcu() for more detailed information on
189  * memory ordering guarantees.
190  */
191 void call_rcu_bh(struct rcu_head *head,
192                  void (*func)(struct rcu_head *head));
193 
194 /**
195  * call_rcu_sched() - Queue an RCU for invocation after sched grace period.
196  * @head: structure to be used for queueing the RCU updates.
197  * @func: actual callback function to be invoked after the grace period
198  *
199  * The callback function will be invoked some time after a full grace
200  * period elapses, in other words after all currently executing RCU
201  * read-side critical sections have completed. call_rcu_sched() assumes
202  * that the read-side critical sections end on enabling of preemption
203  * or on voluntary preemption.
204  * RCU read-side critical sections are delimited by :
205  *  - rcu_read_lock_sched() and  rcu_read_unlock_sched(),
206  *  OR
207  *  anything that disables preemption.
208  *  These may be nested.
209  *
210  * See the description of call_rcu() for more detailed information on
211  * memory ordering guarantees.
212  */
213 void call_rcu_sched(struct rcu_head *head,
214                     void (*func)(struct rcu_head *rcu));
215 
216 void synchronize_sched(void);
217 
218 /*
219  * Structure allowing asynchronous waiting on RCU.
220  */
221 struct rcu_synchronize {
222         struct rcu_head head;
223         struct completion completion;
224 };
225 void wakeme_after_rcu(struct rcu_head *head);
226 
227 /**
228  * call_rcu_tasks() - Queue an RCU for invocation task-based grace period
229  * @head: structure to be used for queueing the RCU updates.
230  * @func: actual callback function to be invoked after the grace period
231  *
232  * The callback function will be invoked some time after a full grace
233  * period elapses, in other words after all currently executing RCU
234  * read-side critical sections have completed. call_rcu_tasks() assumes
235  * that the read-side critical sections end at a voluntary context
236  * switch (not a preemption!), entry into idle, or transition to usermode
237  * execution.  As such, there are no read-side primitives analogous to
238  * rcu_read_lock() and rcu_read_unlock() because this primitive is intended
239  * to determine that all tasks have passed through a safe state, not so
240  * much for data-strcuture synchronization.
241  *
242  * See the description of call_rcu() for more detailed information on
243  * memory ordering guarantees.
244  */
245 void call_rcu_tasks(struct rcu_head *head, void (*func)(struct rcu_head *head));
246 void synchronize_rcu_tasks(void);
247 void rcu_barrier_tasks(void);
248 
249 #ifdef CONFIG_PREEMPT_RCU
250 
251 void __rcu_read_lock(void);
252 void __rcu_read_unlock(void);
253 void rcu_read_unlock_special(struct task_struct *t);
254 void synchronize_rcu(void);
255 
256 /*
257  * Defined as a macro as it is a very low level header included from
258  * areas that don't even know about current.  This gives the rcu_read_lock()
259  * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
260  * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
261  */
262 #define rcu_preempt_depth() (current->rcu_read_lock_nesting)
263 
264 #else /* #ifdef CONFIG_PREEMPT_RCU */
265 
266 static inline void __rcu_read_lock(void)
267 {
268         preempt_disable();
269 }
270 
271 static inline void __rcu_read_unlock(void)
272 {
273         preempt_enable();
274 }
275 
276 static inline void synchronize_rcu(void)
277 {
278         synchronize_sched();
279 }
280 
281 static inline int rcu_preempt_depth(void)
282 {
283         return 0;
284 }
285 
286 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
287 
288 /* Internal to kernel */
289 void rcu_init(void);
290 void rcu_end_inkernel_boot(void);
291 void rcu_sched_qs(void);
292 void rcu_bh_qs(void);
293 void rcu_check_callbacks(int user);
294 struct notifier_block;
295 void rcu_idle_enter(void);
296 void rcu_idle_exit(void);
297 void rcu_irq_enter(void);
298 void rcu_irq_exit(void);
299 int rcu_cpu_notify(struct notifier_block *self,
300                    unsigned long action, void *hcpu);
301 
302 #ifdef CONFIG_RCU_STALL_COMMON
303 void rcu_sysrq_start(void);
304 void rcu_sysrq_end(void);
305 #else /* #ifdef CONFIG_RCU_STALL_COMMON */
306 static inline void rcu_sysrq_start(void)
307 {
308 }
309 static inline void rcu_sysrq_end(void)
310 {
311 }
312 #endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
313 
314 #ifdef CONFIG_RCU_USER_QS
315 void rcu_user_enter(void);
316 void rcu_user_exit(void);
317 #else
318 static inline void rcu_user_enter(void) { }
319 static inline void rcu_user_exit(void) { }
320 static inline void rcu_user_hooks_switch(struct task_struct *prev,
321                                          struct task_struct *next) { }
322 #endif /* CONFIG_RCU_USER_QS */
323 
324 #ifdef CONFIG_RCU_NOCB_CPU
325 void rcu_init_nohz(void);
326 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
327 static inline void rcu_init_nohz(void)
328 {
329 }
330 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
331 
332 /**
333  * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
334  * @a: Code that RCU needs to pay attention to.
335  *
336  * RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden
337  * in the inner idle loop, that is, between the rcu_idle_enter() and
338  * the rcu_idle_exit() -- RCU will happily ignore any such read-side
339  * critical sections.  However, things like powertop need tracepoints
340  * in the inner idle loop.
341  *
342  * This macro provides the way out:  RCU_NONIDLE(do_something_with_RCU())
343  * will tell RCU that it needs to pay attending, invoke its argument
344  * (in this example, a call to the do_something_with_RCU() function),
345  * and then tell RCU to go back to ignoring this CPU.  It is permissible
346  * to nest RCU_NONIDLE() wrappers, but the nesting level is currently
347  * quite limited.  If deeper nesting is required, it will be necessary
348  * to adjust DYNTICK_TASK_NESTING_VALUE accordingly.
349  */
350 #define RCU_NONIDLE(a) \
351         do { \
352                 rcu_irq_enter(); \
353                 do { a; } while (0); \
354                 rcu_irq_exit(); \
355         } while (0)
356 
357 /*
358  * Note a voluntary context switch for RCU-tasks benefit.  This is a
359  * macro rather than an inline function to avoid #include hell.
360  */
361 #ifdef CONFIG_TASKS_RCU
362 #define TASKS_RCU(x) x
363 extern struct srcu_struct tasks_rcu_exit_srcu;
364 #define rcu_note_voluntary_context_switch(t) \
365         do { \
366                 rcu_all_qs(); \
367                 if (ACCESS_ONCE((t)->rcu_tasks_holdout)) \
368                         ACCESS_ONCE((t)->rcu_tasks_holdout) = false; \
369         } while (0)
370 #else /* #ifdef CONFIG_TASKS_RCU */
371 #define TASKS_RCU(x) do { } while (0)
372 #define rcu_note_voluntary_context_switch(t)    rcu_all_qs()
373 #endif /* #else #ifdef CONFIG_TASKS_RCU */
374 
375 /**
376  * cond_resched_rcu_qs - Report potential quiescent states to RCU
377  *
378  * This macro resembles cond_resched(), except that it is defined to
379  * report potential quiescent states to RCU-tasks even if the cond_resched()
380  * machinery were to be shut off, as some advocate for PREEMPT kernels.
381  */
382 #define cond_resched_rcu_qs() \
383 do { \
384         if (!cond_resched()) \
385                 rcu_note_voluntary_context_switch(current); \
386 } while (0)
387 
388 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP)
389 bool __rcu_is_watching(void);
390 #endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP) */
391 
392 /*
393  * Infrastructure to implement the synchronize_() primitives in
394  * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
395  */
396 
397 typedef void call_rcu_func_t(struct rcu_head *head,
398                              void (*func)(struct rcu_head *head));
399 void wait_rcu_gp(call_rcu_func_t crf);
400 
401 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
402 #include <linux/rcutree.h>
403 #elif defined(CONFIG_TINY_RCU)
404 #include <linux/rcutiny.h>
405 #else
406 #error "Unknown RCU implementation specified to kernel configuration"
407 #endif
408 
409 /*
410  * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic
411  * initialization and destruction of rcu_head on the stack. rcu_head structures
412  * allocated dynamically in the heap or defined statically don't need any
413  * initialization.
414  */
415 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
416 void init_rcu_head(struct rcu_head *head);
417 void destroy_rcu_head(struct rcu_head *head);
418 void init_rcu_head_on_stack(struct rcu_head *head);
419 void destroy_rcu_head_on_stack(struct rcu_head *head);
420 #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
421 static inline void init_rcu_head(struct rcu_head *head)
422 {
423 }
424 
425 static inline void destroy_rcu_head(struct rcu_head *head)
426 {
427 }
428 
429 static inline void init_rcu_head_on_stack(struct rcu_head *head)
430 {
431 }
432 
433 static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
434 {
435 }
436 #endif  /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
437 
438 #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
439 bool rcu_lockdep_current_cpu_online(void);
440 #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
441 static inline bool rcu_lockdep_current_cpu_online(void)
442 {
443         return true;
444 }
445 #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
446 
447 #ifdef CONFIG_DEBUG_LOCK_ALLOC
448 
449 static inline void rcu_lock_acquire(struct lockdep_map *map)
450 {
451         lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
452 }
453 
454 static inline void rcu_lock_release(struct lockdep_map *map)
455 {
456         lock_release(map, 1, _THIS_IP_);
457 }
458 
459 extern struct lockdep_map rcu_lock_map;
460 extern struct lockdep_map rcu_bh_lock_map;
461 extern struct lockdep_map rcu_sched_lock_map;
462 extern struct lockdep_map rcu_callback_map;
463 int debug_lockdep_rcu_enabled(void);
464 
465 int rcu_read_lock_held(void);
466 int rcu_read_lock_bh_held(void);
467 
468 /**
469  * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
470  *
471  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
472  * RCU-sched read-side critical section.  In absence of
473  * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
474  * critical section unless it can prove otherwise.  Note that disabling
475  * of preemption (including disabling irqs) counts as an RCU-sched
476  * read-side critical section.  This is useful for debug checks in functions
477  * that required that they be called within an RCU-sched read-side
478  * critical section.
479  *
480  * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
481  * and while lockdep is disabled.
482  *
483  * Note that if the CPU is in the idle loop from an RCU point of
484  * view (ie: that we are in the section between rcu_idle_enter() and
485  * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
486  * did an rcu_read_lock().  The reason for this is that RCU ignores CPUs
487  * that are in such a section, considering these as in extended quiescent
488  * state, so such a CPU is effectively never in an RCU read-side critical
489  * section regardless of what RCU primitives it invokes.  This state of
490  * affairs is required --- we need to keep an RCU-free window in idle
491  * where the CPU may possibly enter into low power mode. This way we can
492  * notice an extended quiescent state to other CPUs that started a grace
493  * period. Otherwise we would delay any grace period as long as we run in
494  * the idle task.
495  *
496  * Similarly, we avoid claiming an SRCU read lock held if the current
497  * CPU is offline.
498  */
499 #ifdef CONFIG_PREEMPT_COUNT
500 static inline int rcu_read_lock_sched_held(void)
501 {
502         int lockdep_opinion = 0;
503 
504         if (!debug_lockdep_rcu_enabled())
505                 return 1;
506         if (!rcu_is_watching())
507                 return 0;
508         if (!rcu_lockdep_current_cpu_online())
509                 return 0;
510         if (debug_locks)
511                 lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
512         return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
513 }
514 #else /* #ifdef CONFIG_PREEMPT_COUNT */
515 static inline int rcu_read_lock_sched_held(void)
516 {
517         return 1;
518 }
519 #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
520 
521 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
522 
523 # define rcu_lock_acquire(a)            do { } while (0)
524 # define rcu_lock_release(a)            do { } while (0)
525 
526 static inline int rcu_read_lock_held(void)
527 {
528         return 1;
529 }
530 
531 static inline int rcu_read_lock_bh_held(void)
532 {
533         return 1;
534 }
535 
536 #ifdef CONFIG_PREEMPT_COUNT
537 static inline int rcu_read_lock_sched_held(void)
538 {
539         return preempt_count() != 0 || irqs_disabled();
540 }
541 #else /* #ifdef CONFIG_PREEMPT_COUNT */
542 static inline int rcu_read_lock_sched_held(void)
543 {
544         return 1;
545 }
546 #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
547 
548 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
549 
550 #ifdef CONFIG_PROVE_RCU
551 
552 /**
553  * rcu_lockdep_assert - emit lockdep splat if specified condition not met
554  * @c: condition to check
555  * @s: informative message
556  */
557 #define rcu_lockdep_assert(c, s)                                        \
558         do {                                                            \
559                 static bool __section(.data.unlikely) __warned;         \
560                 if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
561                         __warned = true;                                \
562                         lockdep_rcu_suspicious(__FILE__, __LINE__, s);  \
563                 }                                                       \
564         } while (0)
565 
566 #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
567 static inline void rcu_preempt_sleep_check(void)
568 {
569         rcu_lockdep_assert(!lock_is_held(&rcu_lock_map),
570                            "Illegal context switch in RCU read-side critical section");
571 }
572 #else /* #ifdef CONFIG_PROVE_RCU */
573 static inline void rcu_preempt_sleep_check(void)
574 {
575 }
576 #endif /* #else #ifdef CONFIG_PROVE_RCU */
577 
578 #define rcu_sleep_check()                                               \
579         do {                                                            \
580                 rcu_preempt_sleep_check();                              \
581                 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map),     \
582                                    "Illegal context switch in RCU-bh read-side critical section"); \
583                 rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map),  \
584                                    "Illegal context switch in RCU-sched read-side critical section"); \
585         } while (0)
586 
587 #else /* #ifdef CONFIG_PROVE_RCU */
588 
589 #define rcu_lockdep_assert(c, s) do { } while (0)
590 #define rcu_sleep_check() do { } while (0)
591 
592 #endif /* #else #ifdef CONFIG_PROVE_RCU */
593 
594 /*
595  * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
596  * and rcu_assign_pointer().  Some of these could be folded into their
597  * callers, but they are left separate in order to ease introduction of
598  * multiple flavors of pointers to match the multiple flavors of RCU
599  * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in
600  * the future.
601  */
602 
603 #ifdef __CHECKER__
604 #define rcu_dereference_sparse(p, space) \
605         ((void)(((typeof(*p) space *)p) == p))
606 #else /* #ifdef __CHECKER__ */
607 #define rcu_dereference_sparse(p, space)
608 #endif /* #else #ifdef __CHECKER__ */
609 
610 #define __rcu_access_pointer(p, space) \
611 ({ \
612         typeof(*p) *_________p1 = (typeof(*p) *__force)ACCESS_ONCE(p); \
613         rcu_dereference_sparse(p, space); \
614         ((typeof(*p) __force __kernel *)(_________p1)); \
615 })
616 #define __rcu_dereference_check(p, c, space) \
617 ({ \
618         /* Dependency order vs. p above. */ \
619         typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \
620         rcu_lockdep_assert(c, "suspicious rcu_dereference_check() usage"); \
621         rcu_dereference_sparse(p, space); \
622         ((typeof(*p) __force __kernel *)(________p1)); \
623 })
624 #define __rcu_dereference_protected(p, c, space) \
625 ({ \
626         rcu_lockdep_assert(c, "suspicious rcu_dereference_protected() usage"); \
627         rcu_dereference_sparse(p, space); \
628         ((typeof(*p) __force __kernel *)(p)); \
629 })
630 
631 #define __rcu_access_index(p, space) \
632 ({ \
633         typeof(p) _________p1 = ACCESS_ONCE(p); \
634         rcu_dereference_sparse(p, space); \
635         (_________p1); \
636 })
637 #define __rcu_dereference_index_check(p, c) \
638 ({ \
639         /* Dependency order vs. p above. */ \
640         typeof(p) _________p1 = lockless_dereference(p); \
641         rcu_lockdep_assert(c, \
642                            "suspicious rcu_dereference_index_check() usage"); \
643         (_________p1); \
644 })
645 
646 /**
647  * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
648  * @v: The value to statically initialize with.
649  */
650 #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
651 
652 /**
653  * lockless_dereference() - safely load a pointer for later dereference
654  * @p: The pointer to load
655  *
656  * Similar to rcu_dereference(), but for situations where the pointed-to
657  * object's lifetime is managed by something other than RCU.  That
658  * "something other" might be reference counting or simple immortality.
659  */
660 #define lockless_dereference(p) \
661 ({ \
662         typeof(p) _________p1 = ACCESS_ONCE(p); \
663         smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
664         (_________p1); \
665 })
666 
667 /**
668  * rcu_assign_pointer() - assign to RCU-protected pointer
669  * @p: pointer to assign to
670  * @v: value to assign (publish)
671  *
672  * Assigns the specified value to the specified RCU-protected
673  * pointer, ensuring that any concurrent RCU readers will see
674  * any prior initialization.
675  *
676  * Inserts memory barriers on architectures that require them
677  * (which is most of them), and also prevents the compiler from
678  * reordering the code that initializes the structure after the pointer
679  * assignment.  More importantly, this call documents which pointers
680  * will be dereferenced by RCU read-side code.
681  *
682  * In some special cases, you may use RCU_INIT_POINTER() instead
683  * of rcu_assign_pointer().  RCU_INIT_POINTER() is a bit faster due
684  * to the fact that it does not constrain either the CPU or the compiler.
685  * That said, using RCU_INIT_POINTER() when you should have used
686  * rcu_assign_pointer() is a very bad thing that results in
687  * impossible-to-diagnose memory corruption.  So please be careful.
688  * See the RCU_INIT_POINTER() comment header for details.
689  *
690  * Note that rcu_assign_pointer() evaluates each of its arguments only
691  * once, appearances notwithstanding.  One of the "extra" evaluations
692  * is in typeof() and the other visible only to sparse (__CHECKER__),
693  * neither of which actually execute the argument.  As with most cpp
694  * macros, this execute-arguments-only-once property is important, so
695  * please be careful when making changes to rcu_assign_pointer() and the
696  * other macros that it invokes.
697  */
698 #define rcu_assign_pointer(p, v) smp_store_release(&p, RCU_INITIALIZER(v))
699 
700 /**
701  * rcu_access_pointer() - fetch RCU pointer with no dereferencing
702  * @p: The pointer to read
703  *
704  * Return the value of the specified RCU-protected pointer, but omit the
705  * smp_read_barrier_depends() and keep the ACCESS_ONCE().  This is useful
706  * when the value of this pointer is accessed, but the pointer is not
707  * dereferenced, for example, when testing an RCU-protected pointer against
708  * NULL.  Although rcu_access_pointer() may also be used in cases where
709  * update-side locks prevent the value of the pointer from changing, you
710  * should instead use rcu_dereference_protected() for this use case.
711  *
712  * It is also permissible to use rcu_access_pointer() when read-side
713  * access to the pointer was removed at least one grace period ago, as
714  * is the case in the context of the RCU callback that is freeing up
715  * the data, or after a synchronize_rcu() returns.  This can be useful
716  * when tearing down multi-linked structures after a grace period
717  * has elapsed.
718  */
719 #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
720 
721 /**
722  * rcu_dereference_check() - rcu_dereference with debug checking
723  * @p: The pointer to read, prior to dereferencing
724  * @c: The conditions under which the dereference will take place
725  *
726  * Do an rcu_dereference(), but check that the conditions under which the
727  * dereference will take place are correct.  Typically the conditions
728  * indicate the various locking conditions that should be held at that
729  * point.  The check should return true if the conditions are satisfied.
730  * An implicit check for being in an RCU read-side critical section
731  * (rcu_read_lock()) is included.
732  *
733  * For example:
734  *
735  *      bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
736  *
737  * could be used to indicate to lockdep that foo->bar may only be dereferenced
738  * if either rcu_read_lock() is held, or that the lock required to replace
739  * the bar struct at foo->bar is held.
740  *
741  * Note that the list of conditions may also include indications of when a lock
742  * need not be held, for example during initialisation or destruction of the
743  * target struct:
744  *
745  *      bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
746  *                                            atomic_read(&foo->usage) == 0);
747  *
748  * Inserts memory barriers on architectures that require them
749  * (currently only the Alpha), prevents the compiler from refetching
750  * (and from merging fetches), and, more importantly, documents exactly
751  * which pointers are protected by RCU and checks that the pointer is
752  * annotated as __rcu.
753  */
754 #define rcu_dereference_check(p, c) \
755         __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
756 
757 /**
758  * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
759  * @p: The pointer to read, prior to dereferencing
760  * @c: The conditions under which the dereference will take place
761  *
762  * This is the RCU-bh counterpart to rcu_dereference_check().
763  */
764 #define rcu_dereference_bh_check(p, c) \
765         __rcu_dereference_check((p), (c) || rcu_read_lock_bh_held(), __rcu)
766 
767 /**
768  * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
769  * @p: The pointer to read, prior to dereferencing
770  * @c: The conditions under which the dereference will take place
771  *
772  * This is the RCU-sched counterpart to rcu_dereference_check().
773  */
774 #define rcu_dereference_sched_check(p, c) \
775         __rcu_dereference_check((p), (c) || rcu_read_lock_sched_held(), \
776                                 __rcu)
777 
778 #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/
779 
780 /*
781  * The tracing infrastructure traces RCU (we want that), but unfortunately
782  * some of the RCU checks causes tracing to lock up the system.
783  *
784  * The tracing version of rcu_dereference_raw() must not call
785  * rcu_read_lock_held().
786  */
787 #define rcu_dereference_raw_notrace(p) __rcu_dereference_check((p), 1, __rcu)
788 
789 /**
790  * rcu_access_index() - fetch RCU index with no dereferencing
791  * @p: The index to read
792  *
793  * Return the value of the specified RCU-protected index, but omit the
794  * smp_read_barrier_depends() and keep the ACCESS_ONCE().  This is useful
795  * when the value of this index is accessed, but the index is not
796  * dereferenced, for example, when testing an RCU-protected index against
797  * -1.  Although rcu_access_index() may also be used in cases where
798  * update-side locks prevent the value of the index from changing, you
799  * should instead use rcu_dereference_index_protected() for this use case.
800  */
801 #define rcu_access_index(p) __rcu_access_index((p), __rcu)
802 
803 /**
804  * rcu_dereference_index_check() - rcu_dereference for indices with debug checking
805  * @p: The pointer to read, prior to dereferencing
806  * @c: The conditions under which the dereference will take place
807  *
808  * Similar to rcu_dereference_check(), but omits the sparse checking.
809  * This allows rcu_dereference_index_check() to be used on integers,
810  * which can then be used as array indices.  Attempting to use
811  * rcu_dereference_check() on an integer will give compiler warnings
812  * because the sparse address-space mechanism relies on dereferencing
813  * the RCU-protected pointer.  Dereferencing integers is not something
814  * that even gcc will put up with.
815  *
816  * Note that this function does not implicitly check for RCU read-side
817  * critical sections.  If this function gains lots of uses, it might
818  * make sense to provide versions for each flavor of RCU, but it does
819  * not make sense as of early 2010.
820  */
821 #define rcu_dereference_index_check(p, c) \
822         __rcu_dereference_index_check((p), (c))
823 
824 /**
825  * rcu_dereference_protected() - fetch RCU pointer when updates prevented
826  * @p: The pointer to read, prior to dereferencing
827  * @c: The conditions under which the dereference will take place
828  *
829  * Return the value of the specified RCU-protected pointer, but omit
830  * both the smp_read_barrier_depends() and the ACCESS_ONCE().  This
831  * is useful in cases where update-side locks prevent the value of the
832  * pointer from changing.  Please note that this primitive does -not-
833  * prevent the compiler from repeating this reference or combining it
834  * with other references, so it should not be used without protection
835  * of appropriate locks.
836  *
837  * This function is only for update-side use.  Using this function
838  * when protected only by rcu_read_lock() will result in infrequent
839  * but very ugly failures.
840  */
841 #define rcu_dereference_protected(p, c) \
842         __rcu_dereference_protected((p), (c), __rcu)
843 
844 
845 /**
846  * rcu_dereference() - fetch RCU-protected pointer for dereferencing
847  * @p: The pointer to read, prior to dereferencing
848  *
849  * This is a simple wrapper around rcu_dereference_check().
850  */
851 #define rcu_dereference(p) rcu_dereference_check(p, 0)
852 
853 /**
854  * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
855  * @p: The pointer to read, prior to dereferencing
856  *
857  * Makes rcu_dereference_check() do the dirty work.
858  */
859 #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
860 
861 /**
862  * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
863  * @p: The pointer to read, prior to dereferencing
864  *
865  * Makes rcu_dereference_check() do the dirty work.
866  */
867 #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
868 
869 /**
870  * rcu_read_lock() - mark the beginning of an RCU read-side critical section
871  *
872  * When synchronize_rcu() is invoked on one CPU while other CPUs
873  * are within RCU read-side critical sections, then the
874  * synchronize_rcu() is guaranteed to block until after all the other
875  * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
876  * on one CPU while other CPUs are within RCU read-side critical
877  * sections, invocation of the corresponding RCU callback is deferred
878  * until after the all the other CPUs exit their critical sections.
879  *
880  * Note, however, that RCU callbacks are permitted to run concurrently
881  * with new RCU read-side critical sections.  One way that this can happen
882  * is via the following sequence of events: (1) CPU 0 enters an RCU
883  * read-side critical section, (2) CPU 1 invokes call_rcu() to register
884  * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
885  * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
886  * callback is invoked.  This is legal, because the RCU read-side critical
887  * section that was running concurrently with the call_rcu() (and which
888  * therefore might be referencing something that the corresponding RCU
889  * callback would free up) has completed before the corresponding
890  * RCU callback is invoked.
891  *
892  * RCU read-side critical sections may be nested.  Any deferred actions
893  * will be deferred until the outermost RCU read-side critical section
894  * completes.
895  *
896  * You can avoid reading and understanding the next paragraph by
897  * following this rule: don't put anything in an rcu_read_lock() RCU
898  * read-side critical section that would block in a !PREEMPT kernel.
899  * But if you want the full story, read on!
900  *
901  * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU),
902  * it is illegal to block while in an RCU read-side critical section.
903  * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPT
904  * kernel builds, RCU read-side critical sections may be preempted,
905  * but explicit blocking is illegal.  Finally, in preemptible RCU
906  * implementations in real-time (with -rt patchset) kernel builds, RCU
907  * read-side critical sections may be preempted and they may also block, but
908  * only when acquiring spinlocks that are subject to priority inheritance.
909  */
910 static inline void rcu_read_lock(void)
911 {
912         __rcu_read_lock();
913         __acquire(RCU);
914         rcu_lock_acquire(&rcu_lock_map);
915         rcu_lockdep_assert(rcu_is_watching(),
916                            "rcu_read_lock() used illegally while idle");
917 }
918 
919 /*
920  * So where is rcu_write_lock()?  It does not exist, as there is no
921  * way for writers to lock out RCU readers.  This is a feature, not
922  * a bug -- this property is what provides RCU's performance benefits.
923  * Of course, writers must coordinate with each other.  The normal
924  * spinlock primitives work well for this, but any other technique may be
925  * used as well.  RCU does not care how the writers keep out of each
926  * others' way, as long as they do so.
927  */
928 
929 /**
930  * rcu_read_unlock() - marks the end of an RCU read-side critical section.
931  *
932  * In most situations, rcu_read_unlock() is immune from deadlock.
933  * However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock()
934  * is responsible for deboosting, which it does via rt_mutex_unlock().
935  * Unfortunately, this function acquires the scheduler's runqueue and
936  * priority-inheritance spinlocks.  This means that deadlock could result
937  * if the caller of rcu_read_unlock() already holds one of these locks or
938  * any lock that is ever acquired while holding them; or any lock which
939  * can be taken from interrupt context because rcu_boost()->rt_mutex_lock()
940  * does not disable irqs while taking ->wait_lock.
941  *
942  * That said, RCU readers are never priority boosted unless they were
943  * preempted.  Therefore, one way to avoid deadlock is to make sure
944  * that preemption never happens within any RCU read-side critical
945  * section whose outermost rcu_read_unlock() is called with one of
946  * rt_mutex_unlock()'s locks held.  Such preemption can be avoided in
947  * a number of ways, for example, by invoking preempt_disable() before
948  * critical section's outermost rcu_read_lock().
949  *
950  * Given that the set of locks acquired by rt_mutex_unlock() might change
951  * at any time, a somewhat more future-proofed approach is to make sure
952  * that that preemption never happens within any RCU read-side critical
953  * section whose outermost rcu_read_unlock() is called with irqs disabled.
954  * This approach relies on the fact that rt_mutex_unlock() currently only
955  * acquires irq-disabled locks.
956  *
957  * The second of these two approaches is best in most situations,
958  * however, the first approach can also be useful, at least to those
959  * developers willing to keep abreast of the set of locks acquired by
960  * rt_mutex_unlock().
961  *
962  * See rcu_read_lock() for more information.
963  */
964 static inline void rcu_read_unlock(void)
965 {
966         rcu_lockdep_assert(rcu_is_watching(),
967                            "rcu_read_unlock() used illegally while idle");
968         __release(RCU);
969         __rcu_read_unlock();
970         rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
971 }
972 
973 /**
974  * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
975  *
976  * This is equivalent of rcu_read_lock(), but to be used when updates
977  * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since
978  * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a
979  * softirq handler to be a quiescent state, a process in RCU read-side
980  * critical section must be protected by disabling softirqs. Read-side
981  * critical sections in interrupt context can use just rcu_read_lock(),
982  * though this should at least be commented to avoid confusing people
983  * reading the code.
984  *
985  * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
986  * must occur in the same context, for example, it is illegal to invoke
987  * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
988  * was invoked from some other task.
989  */
990 static inline void rcu_read_lock_bh(void)
991 {
992         local_bh_disable();
993         __acquire(RCU_BH);
994         rcu_lock_acquire(&rcu_bh_lock_map);
995         rcu_lockdep_assert(rcu_is_watching(),
996                            "rcu_read_lock_bh() used illegally while idle");
997 }
998 
999 /*
1000  * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
1001  *
1002  * See rcu_read_lock_bh() for more information.
1003  */
1004 static inline void rcu_read_unlock_bh(void)
1005 {
1006         rcu_lockdep_assert(rcu_is_watching(),
1007                            "rcu_read_unlock_bh() used illegally while idle");
1008         rcu_lock_release(&rcu_bh_lock_map);
1009         __release(RCU_BH);
1010         local_bh_enable();
1011 }
1012 
1013 /**
1014  * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
1015  *
1016  * This is equivalent of rcu_read_lock(), but to be used when updates
1017  * are being done using call_rcu_sched() or synchronize_rcu_sched().
1018  * Read-side critical sections can also be introduced by anything that
1019  * disables preemption, including local_irq_disable() and friends.
1020  *
1021  * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
1022  * must occur in the same context, for example, it is illegal to invoke
1023  * rcu_read_unlock_sched() from process context if the matching
1024  * rcu_read_lock_sched() was invoked from an NMI handler.
1025  */
1026 static inline void rcu_read_lock_sched(void)
1027 {
1028         preempt_disable();
1029         __acquire(RCU_SCHED);
1030         rcu_lock_acquire(&rcu_sched_lock_map);
1031         rcu_lockdep_assert(rcu_is_watching(),
1032                            "rcu_read_lock_sched() used illegally while idle");
1033 }
1034 
1035 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
1036 static inline notrace void rcu_read_lock_sched_notrace(void)
1037 {
1038         preempt_disable_notrace();
1039         __acquire(RCU_SCHED);
1040 }
1041 
1042 /*
1043  * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
1044  *
1045  * See rcu_read_lock_sched for more information.
1046  */
1047 static inline void rcu_read_unlock_sched(void)
1048 {
1049         rcu_lockdep_assert(rcu_is_watching(),
1050                            "rcu_read_unlock_sched() used illegally while idle");
1051         rcu_lock_release(&rcu_sched_lock_map);
1052         __release(RCU_SCHED);
1053         preempt_enable();
1054 }
1055 
1056 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
1057 static inline notrace void rcu_read_unlock_sched_notrace(void)
1058 {
1059         __release(RCU_SCHED);
1060         preempt_enable_notrace();
1061 }
1062 
1063 /**
1064  * RCU_INIT_POINTER() - initialize an RCU protected pointer
1065  *
1066  * Initialize an RCU-protected pointer in special cases where readers
1067  * do not need ordering constraints on the CPU or the compiler.  These
1068  * special cases are:
1069  *
1070  * 1.   This use of RCU_INIT_POINTER() is NULLing out the pointer -or-
1071  * 2.   The caller has taken whatever steps are required to prevent
1072  *      RCU readers from concurrently accessing this pointer -or-
1073  * 3.   The referenced data structure has already been exposed to
1074  *      readers either at compile time or via rcu_assign_pointer() -and-
1075  *      a.      You have not made -any- reader-visible changes to
1076  *              this structure since then -or-
1077  *      b.      It is OK for readers accessing this structure from its
1078  *              new location to see the old state of the structure.  (For
1079  *              example, the changes were to statistical counters or to
1080  *              other state where exact synchronization is not required.)
1081  *
1082  * Failure to follow these rules governing use of RCU_INIT_POINTER() will
1083  * result in impossible-to-diagnose memory corruption.  As in the structures
1084  * will look OK in crash dumps, but any concurrent RCU readers might
1085  * see pre-initialized values of the referenced data structure.  So
1086  * please be very careful how you use RCU_INIT_POINTER()!!!
1087  *
1088  * If you are creating an RCU-protected linked structure that is accessed
1089  * by a single external-to-structure RCU-protected pointer, then you may
1090  * use RCU_INIT_POINTER() to initialize the internal RCU-protected
1091  * pointers, but you must use rcu_assign_pointer() to initialize the
1092  * external-to-structure pointer -after- you have completely initialized
1093  * the reader-accessible portions of the linked structure.
1094  *
1095  * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
1096  * ordering guarantees for either the CPU or the compiler.
1097  */
1098 #define RCU_INIT_POINTER(p, v) \
1099         do { \
1100                 rcu_dereference_sparse(p, __rcu); \
1101                 p = RCU_INITIALIZER(v); \
1102         } while (0)
1103 
1104 /**
1105  * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
1106  *
1107  * GCC-style initialization for an RCU-protected pointer in a structure field.
1108  */
1109 #define RCU_POINTER_INITIALIZER(p, v) \
1110                 .p = RCU_INITIALIZER(v)
1111 
1112 /*
1113  * Does the specified offset indicate that the corresponding rcu_head
1114  * structure can be handled by kfree_rcu()?
1115  */
1116 #define __is_kfree_rcu_offset(offset) ((offset) < 4096)
1117 
1118 /*
1119  * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain.
1120  */
1121 #define __kfree_rcu(head, offset) \
1122         do { \
1123                 BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \
1124                 kfree_call_rcu(head, (void (*)(struct rcu_head *))(unsigned long)(offset)); \
1125         } while (0)
1126 
1127 /**
1128  * kfree_rcu() - kfree an object after a grace period.
1129  * @ptr:        pointer to kfree
1130  * @rcu_head:   the name of the struct rcu_head within the type of @ptr.
1131  *
1132  * Many rcu callbacks functions just call kfree() on the base structure.
1133  * These functions are trivial, but their size adds up, and furthermore
1134  * when they are used in a kernel module, that module must invoke the
1135  * high-latency rcu_barrier() function at module-unload time.
1136  *
1137  * The kfree_rcu() function handles this issue.  Rather than encoding a
1138  * function address in the embedded rcu_head structure, kfree_rcu() instead
1139  * encodes the offset of the rcu_head structure within the base structure.
1140  * Because the functions are not allowed in the low-order 4096 bytes of
1141  * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
1142  * If the offset is larger than 4095 bytes, a compile-time error will
1143  * be generated in __kfree_rcu().  If this error is triggered, you can
1144  * either fall back to use of call_rcu() or rearrange the structure to
1145  * position the rcu_head structure into the first 4096 bytes.
1146  *
1147  * Note that the allowable offset might decrease in the future, for example,
1148  * to allow something like kmem_cache_free_rcu().
1149  *
1150  * The BUILD_BUG_ON check must not involve any function calls, hence the
1151  * checks are done in macros here.
1152  */
1153 #define kfree_rcu(ptr, rcu_head)                                        \
1154         __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
1155 
1156 #if defined(CONFIG_TINY_RCU) || defined(CONFIG_RCU_NOCB_CPU_ALL)
1157 static inline int rcu_needs_cpu(unsigned long *delta_jiffies)
1158 {
1159         *delta_jiffies = ULONG_MAX;
1160         return 0;
1161 }
1162 #endif /* #if defined(CONFIG_TINY_RCU) || defined(CONFIG_RCU_NOCB_CPU_ALL) */
1163 
1164 #if defined(CONFIG_RCU_NOCB_CPU_ALL)
1165 static inline bool rcu_is_nocb_cpu(int cpu) { return true; }
1166 #elif defined(CONFIG_RCU_NOCB_CPU)
1167 bool rcu_is_nocb_cpu(int cpu);
1168 #else
1169 static inline bool rcu_is_nocb_cpu(int cpu) { return false; }
1170 #endif
1171 
1172 
1173 /* Only for use by adaptive-ticks code. */
1174 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
1175 bool rcu_sys_is_idle(void);
1176 void rcu_sysidle_force_exit(void);
1177 #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
1178 
1179 static inline bool rcu_sys_is_idle(void)
1180 {
1181         return false;
1182 }
1183 
1184 static inline void rcu_sysidle_force_exit(void)
1185 {
1186 }
1187 
1188 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
1189 
1190 
1191 #endif /* __LINUX_RCUPDATE_H */
1192 

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