Version:  2.6.34 2.6.35 2.6.36 2.6.37 2.6.38 2.6.39 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14

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, write to the Free Software
 16  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 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 
 48 #ifdef CONFIG_RCU_TORTURE_TEST
 49 extern int rcutorture_runnable; /* for sysctl */
 50 #endif /* #ifdef CONFIG_RCU_TORTURE_TEST */
 51 
 52 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
 53 void rcutorture_record_test_transition(void);
 54 void rcutorture_record_progress(unsigned long vernum);
 55 void do_trace_rcu_torture_read(const char *rcutorturename,
 56                                struct rcu_head *rhp,
 57                                unsigned long secs,
 58                                unsigned long c_old,
 59                                unsigned long c);
 60 #else
 61 static inline void rcutorture_record_test_transition(void)
 62 {
 63 }
 64 static inline void rcutorture_record_progress(unsigned long vernum)
 65 {
 66 }
 67 #ifdef CONFIG_RCU_TRACE
 68 void do_trace_rcu_torture_read(const char *rcutorturename,
 69                                struct rcu_head *rhp,
 70                                unsigned long secs,
 71                                unsigned long c_old,
 72                                unsigned long c);
 73 #else
 74 #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
 75         do { } while (0)
 76 #endif
 77 #endif
 78 
 79 #define UINT_CMP_GE(a, b)       (UINT_MAX / 2 >= (a) - (b))
 80 #define UINT_CMP_LT(a, b)       (UINT_MAX / 2 < (a) - (b))
 81 #define ULONG_CMP_GE(a, b)      (ULONG_MAX / 2 >= (a) - (b))
 82 #define ULONG_CMP_LT(a, b)      (ULONG_MAX / 2 < (a) - (b))
 83 #define ulong2long(a)           (*(long *)(&(a)))
 84 
 85 /* Exported common interfaces */
 86 
 87 #ifdef CONFIG_PREEMPT_RCU
 88 
 89 /**
 90  * call_rcu() - Queue an RCU callback for invocation after a grace period.
 91  * @head: structure to be used for queueing the RCU updates.
 92  * @func: actual callback function to be invoked after the grace period
 93  *
 94  * The callback function will be invoked some time after a full grace
 95  * period elapses, in other words after all pre-existing RCU read-side
 96  * critical sections have completed.  However, the callback function
 97  * might well execute concurrently with RCU read-side critical sections
 98  * that started after call_rcu() was invoked.  RCU read-side critical
 99  * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
100  * and may be nested.
101  *
102  * Note that all CPUs must agree that the grace period extended beyond
103  * all pre-existing RCU read-side critical section.  On systems with more
104  * than one CPU, this means that when "func()" is invoked, each CPU is
105  * guaranteed to have executed a full memory barrier since the end of its
106  * last RCU read-side critical section whose beginning preceded the call
107  * to call_rcu().  It also means that each CPU executing an RCU read-side
108  * critical section that continues beyond the start of "func()" must have
109  * executed a memory barrier after the call_rcu() but before the beginning
110  * of that RCU read-side critical section.  Note that these guarantees
111  * include CPUs that are offline, idle, or executing in user mode, as
112  * well as CPUs that are executing in the kernel.
113  *
114  * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
115  * resulting RCU callback function "func()", then both CPU A and CPU B are
116  * guaranteed to execute a full memory barrier during the time interval
117  * between the call to call_rcu() and the invocation of "func()" -- even
118  * if CPU A and CPU B are the same CPU (but again only if the system has
119  * more than one CPU).
120  */
121 void call_rcu(struct rcu_head *head,
122               void (*func)(struct rcu_head *head));
123 
124 #else /* #ifdef CONFIG_PREEMPT_RCU */
125 
126 /* In classic RCU, call_rcu() is just call_rcu_sched(). */
127 #define call_rcu        call_rcu_sched
128 
129 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
130 
131 /**
132  * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
133  * @head: structure to be used for queueing the RCU updates.
134  * @func: actual callback function to be invoked after the grace period
135  *
136  * The callback function will be invoked some time after a full grace
137  * period elapses, in other words after all currently executing RCU
138  * read-side critical sections have completed. call_rcu_bh() assumes
139  * that the read-side critical sections end on completion of a softirq
140  * handler. This means that read-side critical sections in process
141  * context must not be interrupted by softirqs. This interface is to be
142  * used when most of the read-side critical sections are in softirq context.
143  * RCU read-side critical sections are delimited by :
144  *  - rcu_read_lock() and  rcu_read_unlock(), if in interrupt context.
145  *  OR
146  *  - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
147  *  These may be nested.
148  *
149  * See the description of call_rcu() for more detailed information on
150  * memory ordering guarantees.
151  */
152 void call_rcu_bh(struct rcu_head *head,
153                  void (*func)(struct rcu_head *head));
154 
155 /**
156  * call_rcu_sched() - Queue an RCU for invocation after sched grace period.
157  * @head: structure to be used for queueing the RCU updates.
158  * @func: actual callback function to be invoked after the grace period
159  *
160  * The callback function will be invoked some time after a full grace
161  * period elapses, in other words after all currently executing RCU
162  * read-side critical sections have completed. call_rcu_sched() assumes
163  * that the read-side critical sections end on enabling of preemption
164  * or on voluntary preemption.
165  * RCU read-side critical sections are delimited by :
166  *  - rcu_read_lock_sched() and  rcu_read_unlock_sched(),
167  *  OR
168  *  anything that disables preemption.
169  *  These may be nested.
170  *
171  * See the description of call_rcu() for more detailed information on
172  * memory ordering guarantees.
173  */
174 void call_rcu_sched(struct rcu_head *head,
175                     void (*func)(struct rcu_head *rcu));
176 
177 void synchronize_sched(void);
178 
179 #ifdef CONFIG_PREEMPT_RCU
180 
181 void __rcu_read_lock(void);
182 void __rcu_read_unlock(void);
183 void rcu_read_unlock_special(struct task_struct *t);
184 void synchronize_rcu(void);
185 
186 /*
187  * Defined as a macro as it is a very low level header included from
188  * areas that don't even know about current.  This gives the rcu_read_lock()
189  * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
190  * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
191  */
192 #define rcu_preempt_depth() (current->rcu_read_lock_nesting)
193 
194 #else /* #ifdef CONFIG_PREEMPT_RCU */
195 
196 static inline void __rcu_read_lock(void)
197 {
198         preempt_disable();
199 }
200 
201 static inline void __rcu_read_unlock(void)
202 {
203         preempt_enable();
204 }
205 
206 static inline void synchronize_rcu(void)
207 {
208         synchronize_sched();
209 }
210 
211 static inline int rcu_preempt_depth(void)
212 {
213         return 0;
214 }
215 
216 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
217 
218 /* Internal to kernel */
219 void rcu_init(void);
220 void rcu_sched_qs(int cpu);
221 void rcu_bh_qs(int cpu);
222 void rcu_check_callbacks(int cpu, int user);
223 struct notifier_block;
224 void rcu_idle_enter(void);
225 void rcu_idle_exit(void);
226 void rcu_irq_enter(void);
227 void rcu_irq_exit(void);
228 
229 #ifdef CONFIG_RCU_USER_QS
230 void rcu_user_enter(void);
231 void rcu_user_exit(void);
232 #else
233 static inline void rcu_user_enter(void) { }
234 static inline void rcu_user_exit(void) { }
235 static inline void rcu_user_hooks_switch(struct task_struct *prev,
236                                          struct task_struct *next) { }
237 #endif /* CONFIG_RCU_USER_QS */
238 
239 /**
240  * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
241  * @a: Code that RCU needs to pay attention to.
242  *
243  * RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden
244  * in the inner idle loop, that is, between the rcu_idle_enter() and
245  * the rcu_idle_exit() -- RCU will happily ignore any such read-side
246  * critical sections.  However, things like powertop need tracepoints
247  * in the inner idle loop.
248  *
249  * This macro provides the way out:  RCU_NONIDLE(do_something_with_RCU())
250  * will tell RCU that it needs to pay attending, invoke its argument
251  * (in this example, a call to the do_something_with_RCU() function),
252  * and then tell RCU to go back to ignoring this CPU.  It is permissible
253  * to nest RCU_NONIDLE() wrappers, but the nesting level is currently
254  * quite limited.  If deeper nesting is required, it will be necessary
255  * to adjust DYNTICK_TASK_NESTING_VALUE accordingly.
256  */
257 #define RCU_NONIDLE(a) \
258         do { \
259                 rcu_irq_enter(); \
260                 do { a; } while (0); \
261                 rcu_irq_exit(); \
262         } while (0)
263 
264 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP)
265 bool __rcu_is_watching(void);
266 #endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP) */
267 
268 /*
269  * Infrastructure to implement the synchronize_() primitives in
270  * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
271  */
272 
273 typedef void call_rcu_func_t(struct rcu_head *head,
274                              void (*func)(struct rcu_head *head));
275 void wait_rcu_gp(call_rcu_func_t crf);
276 
277 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
278 #include <linux/rcutree.h>
279 #elif defined(CONFIG_TINY_RCU)
280 #include <linux/rcutiny.h>
281 #else
282 #error "Unknown RCU implementation specified to kernel configuration"
283 #endif
284 
285 /*
286  * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic
287  * initialization and destruction of rcu_head on the stack. rcu_head structures
288  * allocated dynamically in the heap or defined statically don't need any
289  * initialization.
290  */
291 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
292 void init_rcu_head_on_stack(struct rcu_head *head);
293 void destroy_rcu_head_on_stack(struct rcu_head *head);
294 #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
295 static inline void init_rcu_head_on_stack(struct rcu_head *head)
296 {
297 }
298 
299 static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
300 {
301 }
302 #endif  /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
303 
304 #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
305 bool rcu_lockdep_current_cpu_online(void);
306 #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
307 static inline bool rcu_lockdep_current_cpu_online(void)
308 {
309         return 1;
310 }
311 #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
312 
313 #ifdef CONFIG_DEBUG_LOCK_ALLOC
314 
315 static inline void rcu_lock_acquire(struct lockdep_map *map)
316 {
317         lock_acquire(map, 0, 0, 2, 1, NULL, _THIS_IP_);
318 }
319 
320 static inline void rcu_lock_release(struct lockdep_map *map)
321 {
322         lock_release(map, 1, _THIS_IP_);
323 }
324 
325 extern struct lockdep_map rcu_lock_map;
326 extern struct lockdep_map rcu_bh_lock_map;
327 extern struct lockdep_map rcu_sched_lock_map;
328 extern struct lockdep_map rcu_callback_map;
329 extern int debug_lockdep_rcu_enabled(void);
330 
331 /**
332  * rcu_read_lock_held() - might we be in RCU read-side critical section?
333  *
334  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
335  * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
336  * this assumes we are in an RCU read-side critical section unless it can
337  * prove otherwise.  This is useful for debug checks in functions that
338  * require that they be called within an RCU read-side critical section.
339  *
340  * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
341  * and while lockdep is disabled.
342  *
343  * Note that rcu_read_lock() and the matching rcu_read_unlock() must
344  * occur in the same context, for example, it is illegal to invoke
345  * rcu_read_unlock() in process context if the matching rcu_read_lock()
346  * was invoked from within an irq handler.
347  *
348  * Note that rcu_read_lock() is disallowed if the CPU is either idle or
349  * offline from an RCU perspective, so check for those as well.
350  */
351 static inline int rcu_read_lock_held(void)
352 {
353         if (!debug_lockdep_rcu_enabled())
354                 return 1;
355         if (!rcu_is_watching())
356                 return 0;
357         if (!rcu_lockdep_current_cpu_online())
358                 return 0;
359         return lock_is_held(&rcu_lock_map);
360 }
361 
362 /*
363  * rcu_read_lock_bh_held() is defined out of line to avoid #include-file
364  * hell.
365  */
366 int rcu_read_lock_bh_held(void);
367 
368 /**
369  * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
370  *
371  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
372  * RCU-sched read-side critical section.  In absence of
373  * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
374  * critical section unless it can prove otherwise.  Note that disabling
375  * of preemption (including disabling irqs) counts as an RCU-sched
376  * read-side critical section.  This is useful for debug checks in functions
377  * that required that they be called within an RCU-sched read-side
378  * critical section.
379  *
380  * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
381  * and while lockdep is disabled.
382  *
383  * Note that if the CPU is in the idle loop from an RCU point of
384  * view (ie: that we are in the section between rcu_idle_enter() and
385  * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
386  * did an rcu_read_lock().  The reason for this is that RCU ignores CPUs
387  * that are in such a section, considering these as in extended quiescent
388  * state, so such a CPU is effectively never in an RCU read-side critical
389  * section regardless of what RCU primitives it invokes.  This state of
390  * affairs is required --- we need to keep an RCU-free window in idle
391  * where the CPU may possibly enter into low power mode. This way we can
392  * notice an extended quiescent state to other CPUs that started a grace
393  * period. Otherwise we would delay any grace period as long as we run in
394  * the idle task.
395  *
396  * Similarly, we avoid claiming an SRCU read lock held if the current
397  * CPU is offline.
398  */
399 #ifdef CONFIG_PREEMPT_COUNT
400 static inline int rcu_read_lock_sched_held(void)
401 {
402         int lockdep_opinion = 0;
403 
404         if (!debug_lockdep_rcu_enabled())
405                 return 1;
406         if (!rcu_is_watching())
407                 return 0;
408         if (!rcu_lockdep_current_cpu_online())
409                 return 0;
410         if (debug_locks)
411                 lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
412         return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
413 }
414 #else /* #ifdef CONFIG_PREEMPT_COUNT */
415 static inline int rcu_read_lock_sched_held(void)
416 {
417         return 1;
418 }
419 #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
420 
421 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
422 
423 # define rcu_lock_acquire(a)            do { } while (0)
424 # define rcu_lock_release(a)            do { } while (0)
425 
426 static inline int rcu_read_lock_held(void)
427 {
428         return 1;
429 }
430 
431 static inline int rcu_read_lock_bh_held(void)
432 {
433         return 1;
434 }
435 
436 #ifdef CONFIG_PREEMPT_COUNT
437 static inline int rcu_read_lock_sched_held(void)
438 {
439         return preempt_count() != 0 || irqs_disabled();
440 }
441 #else /* #ifdef CONFIG_PREEMPT_COUNT */
442 static inline int rcu_read_lock_sched_held(void)
443 {
444         return 1;
445 }
446 #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
447 
448 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
449 
450 #ifdef CONFIG_PROVE_RCU
451 
452 /**
453  * rcu_lockdep_assert - emit lockdep splat if specified condition not met
454  * @c: condition to check
455  * @s: informative message
456  */
457 #define rcu_lockdep_assert(c, s)                                        \
458         do {                                                            \
459                 static bool __section(.data.unlikely) __warned;         \
460                 if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
461                         __warned = true;                                \
462                         lockdep_rcu_suspicious(__FILE__, __LINE__, s);  \
463                 }                                                       \
464         } while (0)
465 
466 #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
467 static inline void rcu_preempt_sleep_check(void)
468 {
469         rcu_lockdep_assert(!lock_is_held(&rcu_lock_map),
470                            "Illegal context switch in RCU read-side critical section");
471 }
472 #else /* #ifdef CONFIG_PROVE_RCU */
473 static inline void rcu_preempt_sleep_check(void)
474 {
475 }
476 #endif /* #else #ifdef CONFIG_PROVE_RCU */
477 
478 #define rcu_sleep_check()                                               \
479         do {                                                            \
480                 rcu_preempt_sleep_check();                              \
481                 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map),     \
482                                    "Illegal context switch in RCU-bh"   \
483                                    " read-side critical section");      \
484                 rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map),  \
485                                    "Illegal context switch in RCU-sched"\
486                                    " read-side critical section");      \
487         } while (0)
488 
489 #else /* #ifdef CONFIG_PROVE_RCU */
490 
491 #define rcu_lockdep_assert(c, s) do { } while (0)
492 #define rcu_sleep_check() do { } while (0)
493 
494 #endif /* #else #ifdef CONFIG_PROVE_RCU */
495 
496 /*
497  * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
498  * and rcu_assign_pointer().  Some of these could be folded into their
499  * callers, but they are left separate in order to ease introduction of
500  * multiple flavors of pointers to match the multiple flavors of RCU
501  * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in
502  * the future.
503  */
504 
505 #ifdef __CHECKER__
506 #define rcu_dereference_sparse(p, space) \
507         ((void)(((typeof(*p) space *)p) == p))
508 #else /* #ifdef __CHECKER__ */
509 #define rcu_dereference_sparse(p, space)
510 #endif /* #else #ifdef __CHECKER__ */
511 
512 #define __rcu_access_pointer(p, space) \
513         ({ \
514                 typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
515                 rcu_dereference_sparse(p, space); \
516                 ((typeof(*p) __force __kernel *)(_________p1)); \
517         })
518 #define __rcu_dereference_check(p, c, space) \
519         ({ \
520                 typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
521                 rcu_lockdep_assert(c, "suspicious rcu_dereference_check()" \
522                                       " usage"); \
523                 rcu_dereference_sparse(p, space); \
524                 smp_read_barrier_depends(); \
525                 ((typeof(*p) __force __kernel *)(_________p1)); \
526         })
527 #define __rcu_dereference_protected(p, c, space) \
528         ({ \
529                 rcu_lockdep_assert(c, "suspicious rcu_dereference_protected()" \
530                                       " usage"); \
531                 rcu_dereference_sparse(p, space); \
532                 ((typeof(*p) __force __kernel *)(p)); \
533         })
534 
535 #define __rcu_access_index(p, space) \
536         ({ \
537                 typeof(p) _________p1 = ACCESS_ONCE(p); \
538                 rcu_dereference_sparse(p, space); \
539                 (_________p1); \
540         })
541 #define __rcu_dereference_index_check(p, c) \
542         ({ \
543                 typeof(p) _________p1 = ACCESS_ONCE(p); \
544                 rcu_lockdep_assert(c, \
545                                    "suspicious rcu_dereference_index_check()" \
546                                    " usage"); \
547                 smp_read_barrier_depends(); \
548                 (_________p1); \
549         })
550 
551 /**
552  * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
553  * @v: The value to statically initialize with.
554  */
555 #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
556 
557 /**
558  * rcu_assign_pointer() - assign to RCU-protected pointer
559  * @p: pointer to assign to
560  * @v: value to assign (publish)
561  *
562  * Assigns the specified value to the specified RCU-protected
563  * pointer, ensuring that any concurrent RCU readers will see
564  * any prior initialization.
565  *
566  * Inserts memory barriers on architectures that require them
567  * (which is most of them), and also prevents the compiler from
568  * reordering the code that initializes the structure after the pointer
569  * assignment.  More importantly, this call documents which pointers
570  * will be dereferenced by RCU read-side code.
571  *
572  * In some special cases, you may use RCU_INIT_POINTER() instead
573  * of rcu_assign_pointer().  RCU_INIT_POINTER() is a bit faster due
574  * to the fact that it does not constrain either the CPU or the compiler.
575  * That said, using RCU_INIT_POINTER() when you should have used
576  * rcu_assign_pointer() is a very bad thing that results in
577  * impossible-to-diagnose memory corruption.  So please be careful.
578  * See the RCU_INIT_POINTER() comment header for details.
579  *
580  * Note that rcu_assign_pointer() evaluates each of its arguments only
581  * once, appearances notwithstanding.  One of the "extra" evaluations
582  * is in typeof() and the other visible only to sparse (__CHECKER__),
583  * neither of which actually execute the argument.  As with most cpp
584  * macros, this execute-arguments-only-once property is important, so
585  * please be careful when making changes to rcu_assign_pointer() and the
586  * other macros that it invokes.
587  */
588 #define rcu_assign_pointer(p, v) \
589         do { \
590                 smp_wmb(); \
591                 ACCESS_ONCE(p) = RCU_INITIALIZER(v); \
592         } while (0)
593 
594 
595 /**
596  * rcu_access_pointer() - fetch RCU pointer with no dereferencing
597  * @p: The pointer to read
598  *
599  * Return the value of the specified RCU-protected pointer, but omit the
600  * smp_read_barrier_depends() and keep the ACCESS_ONCE().  This is useful
601  * when the value of this pointer is accessed, but the pointer is not
602  * dereferenced, for example, when testing an RCU-protected pointer against
603  * NULL.  Although rcu_access_pointer() may also be used in cases where
604  * update-side locks prevent the value of the pointer from changing, you
605  * should instead use rcu_dereference_protected() for this use case.
606  *
607  * It is also permissible to use rcu_access_pointer() when read-side
608  * access to the pointer was removed at least one grace period ago, as
609  * is the case in the context of the RCU callback that is freeing up
610  * the data, or after a synchronize_rcu() returns.  This can be useful
611  * when tearing down multi-linked structures after a grace period
612  * has elapsed.
613  */
614 #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
615 
616 /**
617  * rcu_dereference_check() - rcu_dereference with debug checking
618  * @p: The pointer to read, prior to dereferencing
619  * @c: The conditions under which the dereference will take place
620  *
621  * Do an rcu_dereference(), but check that the conditions under which the
622  * dereference will take place are correct.  Typically the conditions
623  * indicate the various locking conditions that should be held at that
624  * point.  The check should return true if the conditions are satisfied.
625  * An implicit check for being in an RCU read-side critical section
626  * (rcu_read_lock()) is included.
627  *
628  * For example:
629  *
630  *      bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
631  *
632  * could be used to indicate to lockdep that foo->bar may only be dereferenced
633  * if either rcu_read_lock() is held, or that the lock required to replace
634  * the bar struct at foo->bar is held.
635  *
636  * Note that the list of conditions may also include indications of when a lock
637  * need not be held, for example during initialisation or destruction of the
638  * target struct:
639  *
640  *      bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
641  *                                            atomic_read(&foo->usage) == 0);
642  *
643  * Inserts memory barriers on architectures that require them
644  * (currently only the Alpha), prevents the compiler from refetching
645  * (and from merging fetches), and, more importantly, documents exactly
646  * which pointers are protected by RCU and checks that the pointer is
647  * annotated as __rcu.
648  */
649 #define rcu_dereference_check(p, c) \
650         __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)
651 
652 /**
653  * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
654  * @p: The pointer to read, prior to dereferencing
655  * @c: The conditions under which the dereference will take place
656  *
657  * This is the RCU-bh counterpart to rcu_dereference_check().
658  */
659 #define rcu_dereference_bh_check(p, c) \
660         __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu)
661 
662 /**
663  * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
664  * @p: The pointer to read, prior to dereferencing
665  * @c: The conditions under which the dereference will take place
666  *
667  * This is the RCU-sched counterpart to rcu_dereference_check().
668  */
669 #define rcu_dereference_sched_check(p, c) \
670         __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \
671                                 __rcu)
672 
673 #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/
674 
675 /*
676  * The tracing infrastructure traces RCU (we want that), but unfortunately
677  * some of the RCU checks causes tracing to lock up the system.
678  *
679  * The tracing version of rcu_dereference_raw() must not call
680  * rcu_read_lock_held().
681  */
682 #define rcu_dereference_raw_notrace(p) __rcu_dereference_check((p), 1, __rcu)
683 
684 /**
685  * rcu_access_index() - fetch RCU index with no dereferencing
686  * @p: The index to read
687  *
688  * Return the value of the specified RCU-protected index, but omit the
689  * smp_read_barrier_depends() and keep the ACCESS_ONCE().  This is useful
690  * when the value of this index is accessed, but the index is not
691  * dereferenced, for example, when testing an RCU-protected index against
692  * -1.  Although rcu_access_index() may also be used in cases where
693  * update-side locks prevent the value of the index from changing, you
694  * should instead use rcu_dereference_index_protected() for this use case.
695  */
696 #define rcu_access_index(p) __rcu_access_index((p), __rcu)
697 
698 /**
699  * rcu_dereference_index_check() - rcu_dereference for indices with debug checking
700  * @p: The pointer to read, prior to dereferencing
701  * @c: The conditions under which the dereference will take place
702  *
703  * Similar to rcu_dereference_check(), but omits the sparse checking.
704  * This allows rcu_dereference_index_check() to be used on integers,
705  * which can then be used as array indices.  Attempting to use
706  * rcu_dereference_check() on an integer will give compiler warnings
707  * because the sparse address-space mechanism relies on dereferencing
708  * the RCU-protected pointer.  Dereferencing integers is not something
709  * that even gcc will put up with.
710  *
711  * Note that this function does not implicitly check for RCU read-side
712  * critical sections.  If this function gains lots of uses, it might
713  * make sense to provide versions for each flavor of RCU, but it does
714  * not make sense as of early 2010.
715  */
716 #define rcu_dereference_index_check(p, c) \
717         __rcu_dereference_index_check((p), (c))
718 
719 /**
720  * rcu_dereference_protected() - fetch RCU pointer when updates prevented
721  * @p: The pointer to read, prior to dereferencing
722  * @c: The conditions under which the dereference will take place
723  *
724  * Return the value of the specified RCU-protected pointer, but omit
725  * both the smp_read_barrier_depends() and the ACCESS_ONCE().  This
726  * is useful in cases where update-side locks prevent the value of the
727  * pointer from changing.  Please note that this primitive does -not-
728  * prevent the compiler from repeating this reference or combining it
729  * with other references, so it should not be used without protection
730  * of appropriate locks.
731  *
732  * This function is only for update-side use.  Using this function
733  * when protected only by rcu_read_lock() will result in infrequent
734  * but very ugly failures.
735  */
736 #define rcu_dereference_protected(p, c) \
737         __rcu_dereference_protected((p), (c), __rcu)
738 
739 
740 /**
741  * rcu_dereference() - fetch RCU-protected pointer for dereferencing
742  * @p: The pointer to read, prior to dereferencing
743  *
744  * This is a simple wrapper around rcu_dereference_check().
745  */
746 #define rcu_dereference(p) rcu_dereference_check(p, 0)
747 
748 /**
749  * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
750  * @p: The pointer to read, prior to dereferencing
751  *
752  * Makes rcu_dereference_check() do the dirty work.
753  */
754 #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
755 
756 /**
757  * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
758  * @p: The pointer to read, prior to dereferencing
759  *
760  * Makes rcu_dereference_check() do the dirty work.
761  */
762 #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
763 
764 /**
765  * rcu_read_lock() - mark the beginning of an RCU read-side critical section
766  *
767  * When synchronize_rcu() is invoked on one CPU while other CPUs
768  * are within RCU read-side critical sections, then the
769  * synchronize_rcu() is guaranteed to block until after all the other
770  * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
771  * on one CPU while other CPUs are within RCU read-side critical
772  * sections, invocation of the corresponding RCU callback is deferred
773  * until after the all the other CPUs exit their critical sections.
774  *
775  * Note, however, that RCU callbacks are permitted to run concurrently
776  * with new RCU read-side critical sections.  One way that this can happen
777  * is via the following sequence of events: (1) CPU 0 enters an RCU
778  * read-side critical section, (2) CPU 1 invokes call_rcu() to register
779  * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
780  * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
781  * callback is invoked.  This is legal, because the RCU read-side critical
782  * section that was running concurrently with the call_rcu() (and which
783  * therefore might be referencing something that the corresponding RCU
784  * callback would free up) has completed before the corresponding
785  * RCU callback is invoked.
786  *
787  * RCU read-side critical sections may be nested.  Any deferred actions
788  * will be deferred until the outermost RCU read-side critical section
789  * completes.
790  *
791  * You can avoid reading and understanding the next paragraph by
792  * following this rule: don't put anything in an rcu_read_lock() RCU
793  * read-side critical section that would block in a !PREEMPT kernel.
794  * But if you want the full story, read on!
795  *
796  * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it
797  * is illegal to block while in an RCU read-side critical section.  In
798  * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU)
799  * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may
800  * be preempted, but explicit blocking is illegal.  Finally, in preemptible
801  * RCU implementations in real-time (with -rt patchset) kernel builds,
802  * RCU read-side critical sections may be preempted and they may also
803  * block, but only when acquiring spinlocks that are subject to priority
804  * inheritance.
805  */
806 static inline void rcu_read_lock(void)
807 {
808         __rcu_read_lock();
809         __acquire(RCU);
810         rcu_lock_acquire(&rcu_lock_map);
811         rcu_lockdep_assert(rcu_is_watching(),
812                            "rcu_read_lock() used illegally while idle");
813 }
814 
815 /*
816  * So where is rcu_write_lock()?  It does not exist, as there is no
817  * way for writers to lock out RCU readers.  This is a feature, not
818  * a bug -- this property is what provides RCU's performance benefits.
819  * Of course, writers must coordinate with each other.  The normal
820  * spinlock primitives work well for this, but any other technique may be
821  * used as well.  RCU does not care how the writers keep out of each
822  * others' way, as long as they do so.
823  */
824 
825 /**
826  * rcu_read_unlock() - marks the end of an RCU read-side critical section.
827  *
828  * See rcu_read_lock() for more information.
829  */
830 static inline void rcu_read_unlock(void)
831 {
832         rcu_lockdep_assert(rcu_is_watching(),
833                            "rcu_read_unlock() used illegally while idle");
834         rcu_lock_release(&rcu_lock_map);
835         __release(RCU);
836         __rcu_read_unlock();
837 }
838 
839 /**
840  * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
841  *
842  * This is equivalent of rcu_read_lock(), but to be used when updates
843  * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since
844  * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a
845  * softirq handler to be a quiescent state, a process in RCU read-side
846  * critical section must be protected by disabling softirqs. Read-side
847  * critical sections in interrupt context can use just rcu_read_lock(),
848  * though this should at least be commented to avoid confusing people
849  * reading the code.
850  *
851  * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
852  * must occur in the same context, for example, it is illegal to invoke
853  * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
854  * was invoked from some other task.
855  */
856 static inline void rcu_read_lock_bh(void)
857 {
858         local_bh_disable();
859         __acquire(RCU_BH);
860         rcu_lock_acquire(&rcu_bh_lock_map);
861         rcu_lockdep_assert(rcu_is_watching(),
862                            "rcu_read_lock_bh() used illegally while idle");
863 }
864 
865 /*
866  * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
867  *
868  * See rcu_read_lock_bh() for more information.
869  */
870 static inline void rcu_read_unlock_bh(void)
871 {
872         rcu_lockdep_assert(rcu_is_watching(),
873                            "rcu_read_unlock_bh() used illegally while idle");
874         rcu_lock_release(&rcu_bh_lock_map);
875         __release(RCU_BH);
876         local_bh_enable();
877 }
878 
879 /**
880  * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
881  *
882  * This is equivalent of rcu_read_lock(), but to be used when updates
883  * are being done using call_rcu_sched() or synchronize_rcu_sched().
884  * Read-side critical sections can also be introduced by anything that
885  * disables preemption, including local_irq_disable() and friends.
886  *
887  * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
888  * must occur in the same context, for example, it is illegal to invoke
889  * rcu_read_unlock_sched() from process context if the matching
890  * rcu_read_lock_sched() was invoked from an NMI handler.
891  */
892 static inline void rcu_read_lock_sched(void)
893 {
894         preempt_disable();
895         __acquire(RCU_SCHED);
896         rcu_lock_acquire(&rcu_sched_lock_map);
897         rcu_lockdep_assert(rcu_is_watching(),
898                            "rcu_read_lock_sched() used illegally while idle");
899 }
900 
901 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
902 static inline notrace void rcu_read_lock_sched_notrace(void)
903 {
904         preempt_disable_notrace();
905         __acquire(RCU_SCHED);
906 }
907 
908 /*
909  * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
910  *
911  * See rcu_read_lock_sched for more information.
912  */
913 static inline void rcu_read_unlock_sched(void)
914 {
915         rcu_lockdep_assert(rcu_is_watching(),
916                            "rcu_read_unlock_sched() used illegally while idle");
917         rcu_lock_release(&rcu_sched_lock_map);
918         __release(RCU_SCHED);
919         preempt_enable();
920 }
921 
922 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
923 static inline notrace void rcu_read_unlock_sched_notrace(void)
924 {
925         __release(RCU_SCHED);
926         preempt_enable_notrace();
927 }
928 
929 /**
930  * RCU_INIT_POINTER() - initialize an RCU protected pointer
931  *
932  * Initialize an RCU-protected pointer in special cases where readers
933  * do not need ordering constraints on the CPU or the compiler.  These
934  * special cases are:
935  *
936  * 1.   This use of RCU_INIT_POINTER() is NULLing out the pointer -or-
937  * 2.   The caller has taken whatever steps are required to prevent
938  *      RCU readers from concurrently accessing this pointer -or-
939  * 3.   The referenced data structure has already been exposed to
940  *      readers either at compile time or via rcu_assign_pointer() -and-
941  *      a.      You have not made -any- reader-visible changes to
942  *              this structure since then -or-
943  *      b.      It is OK for readers accessing this structure from its
944  *              new location to see the old state of the structure.  (For
945  *              example, the changes were to statistical counters or to
946  *              other state where exact synchronization is not required.)
947  *
948  * Failure to follow these rules governing use of RCU_INIT_POINTER() will
949  * result in impossible-to-diagnose memory corruption.  As in the structures
950  * will look OK in crash dumps, but any concurrent RCU readers might
951  * see pre-initialized values of the referenced data structure.  So
952  * please be very careful how you use RCU_INIT_POINTER()!!!
953  *
954  * If you are creating an RCU-protected linked structure that is accessed
955  * by a single external-to-structure RCU-protected pointer, then you may
956  * use RCU_INIT_POINTER() to initialize the internal RCU-protected
957  * pointers, but you must use rcu_assign_pointer() to initialize the
958  * external-to-structure pointer -after- you have completely initialized
959  * the reader-accessible portions of the linked structure.
960  */
961 #define RCU_INIT_POINTER(p, v) \
962         do { \
963                 p = RCU_INITIALIZER(v); \
964         } while (0)
965 
966 /**
967  * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
968  *
969  * GCC-style initialization for an RCU-protected pointer in a structure field.
970  */
971 #define RCU_POINTER_INITIALIZER(p, v) \
972                 .p = RCU_INITIALIZER(v)
973 
974 /*
975  * Does the specified offset indicate that the corresponding rcu_head
976  * structure can be handled by kfree_rcu()?
977  */
978 #define __is_kfree_rcu_offset(offset) ((offset) < 4096)
979 
980 /*
981  * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain.
982  */
983 #define __kfree_rcu(head, offset) \
984         do { \
985                 BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \
986                 kfree_call_rcu(head, (void (*)(struct rcu_head *))(unsigned long)(offset)); \
987         } while (0)
988 
989 /**
990  * kfree_rcu() - kfree an object after a grace period.
991  * @ptr:        pointer to kfree
992  * @rcu_head:   the name of the struct rcu_head within the type of @ptr.
993  *
994  * Many rcu callbacks functions just call kfree() on the base structure.
995  * These functions are trivial, but their size adds up, and furthermore
996  * when they are used in a kernel module, that module must invoke the
997  * high-latency rcu_barrier() function at module-unload time.
998  *
999  * The kfree_rcu() function handles this issue.  Rather than encoding a
1000  * function address in the embedded rcu_head structure, kfree_rcu() instead
1001  * encodes the offset of the rcu_head structure within the base structure.
1002  * Because the functions are not allowed in the low-order 4096 bytes of
1003  * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
1004  * If the offset is larger than 4095 bytes, a compile-time error will
1005  * be generated in __kfree_rcu().  If this error is triggered, you can
1006  * either fall back to use of call_rcu() or rearrange the structure to
1007  * position the rcu_head structure into the first 4096 bytes.
1008  *
1009  * Note that the allowable offset might decrease in the future, for example,
1010  * to allow something like kmem_cache_free_rcu().
1011  *
1012  * The BUILD_BUG_ON check must not involve any function calls, hence the
1013  * checks are done in macros here.
1014  */
1015 #define kfree_rcu(ptr, rcu_head)                                        \
1016         __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
1017 
1018 #ifdef CONFIG_RCU_NOCB_CPU
1019 bool rcu_is_nocb_cpu(int cpu);
1020 #else
1021 static inline bool rcu_is_nocb_cpu(int cpu) { return false; }
1022 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
1023 
1024 
1025 /* Only for use by adaptive-ticks code. */
1026 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
1027 bool rcu_sys_is_idle(void);
1028 void rcu_sysidle_force_exit(void);
1029 #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
1030 
1031 static inline bool rcu_sys_is_idle(void)
1032 {
1033         return false;
1034 }
1035 
1036 static inline void rcu_sysidle_force_exit(void)
1037 {
1038 }
1039 
1040 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
1041 
1042 
1043 #endif /* __LINUX_RCUPDATE_H */
1044 

This page was automatically generated by LXR 0.3.1 (source).  •  Linux is a registered trademark of Linus Torvalds  •  Contact us