1 /* SPDX-License-Identifier: GPL-2.0+ */
3 * Read-Copy Update mechanism for mutual exclusion
5 * Copyright IBM Corporation, 2001
7 * Author: Dipankar Sarma <dipankar@in.ibm.com>
9 * Based on the original work by Paul McKenney <paulmck@vnet.ibm.com>
10 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
12 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
13 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
15 * For detailed explanation of Read-Copy Update mechanism see -
16 * http://lse.sourceforge.net/locking/rcupdate.html
20 #ifndef __LINUX_RCUPDATE_H
21 #define __LINUX_RCUPDATE_H
23 #include <linux/types.h>
24 #include <linux/compiler.h>
25 #include <linux/atomic.h>
26 #include <linux/irqflags.h>
27 #include <linux/preempt.h>
28 #include <linux/bottom_half.h>
29 #include <linux/lockdep.h>
30 #include <asm/processor.h>
31 #include <linux/cpumask.h>
32 #include <linux/context_tracking_irq.h>
34 #define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))
35 #define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b))
36 #define ulong2long(a) (*(long *)(&(a)))
37 #define USHORT_CMP_GE(a, b) (USHRT_MAX / 2 >= (unsigned short)((a) - (b)))
38 #define USHORT_CMP_LT(a, b) (USHRT_MAX / 2 < (unsigned short)((a) - (b)))
40 /* Exported common interfaces */
41 void call_rcu(struct rcu_head *head, rcu_callback_t func);
42 void rcu_barrier_tasks(void);
43 void rcu_barrier_tasks_rude(void);
44 void synchronize_rcu(void);
46 struct rcu_gp_oldstate;
47 unsigned long get_completed_synchronize_rcu(void);
48 void get_completed_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp);
50 // Maximum number of unsigned long values corresponding to
51 // not-yet-completed RCU grace periods.
52 #define NUM_ACTIVE_RCU_POLL_OLDSTATE 2
55 * same_state_synchronize_rcu - Are two old-state values identical?
56 * @oldstate1: First old-state value.
57 * @oldstate2: Second old-state value.
59 * The two old-state values must have been obtained from either
60 * get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or
61 * get_completed_synchronize_rcu(). Returns @true if the two values are
62 * identical and @false otherwise. This allows structures whose lifetimes
63 * are tracked by old-state values to push these values to a list header,
64 * allowing those structures to be slightly smaller.
66 static inline bool same_state_synchronize_rcu(unsigned long oldstate1, unsigned long oldstate2)
68 return oldstate1 == oldstate2;
71 #ifdef CONFIG_PREEMPT_RCU
73 void __rcu_read_lock(void);
74 void __rcu_read_unlock(void);
77 * Defined as a macro as it is a very low level header included from
78 * areas that don't even know about current. This gives the rcu_read_lock()
79 * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
80 * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
82 #define rcu_preempt_depth() READ_ONCE(current->rcu_read_lock_nesting)
84 #else /* #ifdef CONFIG_PREEMPT_RCU */
86 #ifdef CONFIG_TINY_RCU
87 #define rcu_read_unlock_strict() do { } while (0)
89 void rcu_read_unlock_strict(void);
92 static inline void __rcu_read_lock(void)
97 static inline void __rcu_read_unlock(void)
100 if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
101 rcu_read_unlock_strict();
104 static inline int rcu_preempt_depth(void)
109 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
111 #ifdef CONFIG_RCU_LAZY
112 void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func);
114 static inline void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func)
116 call_rcu(head, func);
120 /* Internal to kernel */
122 extern int rcu_scheduler_active;
123 void rcu_sched_clock_irq(int user);
124 void rcu_report_dead(unsigned int cpu);
125 void rcutree_migrate_callbacks(int cpu);
127 #ifdef CONFIG_TASKS_RCU_GENERIC
128 void rcu_init_tasks_generic(void);
130 static inline void rcu_init_tasks_generic(void) { }
133 #ifdef CONFIG_RCU_STALL_COMMON
134 void rcu_sysrq_start(void);
135 void rcu_sysrq_end(void);
136 #else /* #ifdef CONFIG_RCU_STALL_COMMON */
137 static inline void rcu_sysrq_start(void) { }
138 static inline void rcu_sysrq_end(void) { }
139 #endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
141 #if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK))
142 void rcu_irq_work_resched(void);
144 static inline void rcu_irq_work_resched(void) { }
147 #ifdef CONFIG_RCU_NOCB_CPU
148 void rcu_init_nohz(void);
149 int rcu_nocb_cpu_offload(int cpu);
150 int rcu_nocb_cpu_deoffload(int cpu);
151 void rcu_nocb_flush_deferred_wakeup(void);
152 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
153 static inline void rcu_init_nohz(void) { }
154 static inline int rcu_nocb_cpu_offload(int cpu) { return -EINVAL; }
155 static inline int rcu_nocb_cpu_deoffload(int cpu) { return 0; }
156 static inline void rcu_nocb_flush_deferred_wakeup(void) { }
157 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
160 * Note a quasi-voluntary context switch for RCU-tasks's benefit.
161 * This is a macro rather than an inline function to avoid #include hell.
163 #ifdef CONFIG_TASKS_RCU_GENERIC
165 # ifdef CONFIG_TASKS_RCU
166 # define rcu_tasks_classic_qs(t, preempt) \
168 if (!(preempt) && READ_ONCE((t)->rcu_tasks_holdout)) \
169 WRITE_ONCE((t)->rcu_tasks_holdout, false); \
171 void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
172 void synchronize_rcu_tasks(void);
174 # define rcu_tasks_classic_qs(t, preempt) do { } while (0)
175 # define call_rcu_tasks call_rcu
176 # define synchronize_rcu_tasks synchronize_rcu
179 # ifdef CONFIG_TASKS_TRACE_RCU
180 // Bits for ->trc_reader_special.b.need_qs field.
181 #define TRC_NEED_QS 0x1 // Task needs a quiescent state.
182 #define TRC_NEED_QS_CHECKED 0x2 // Task has been checked for needing quiescent state.
184 u8 rcu_trc_cmpxchg_need_qs(struct task_struct *t, u8 old, u8 new);
185 void rcu_tasks_trace_qs_blkd(struct task_struct *t);
187 # define rcu_tasks_trace_qs(t) \
189 int ___rttq_nesting = READ_ONCE((t)->trc_reader_nesting); \
191 if (likely(!READ_ONCE((t)->trc_reader_special.b.need_qs)) && \
192 likely(!___rttq_nesting)) { \
193 rcu_trc_cmpxchg_need_qs((t), 0, TRC_NEED_QS_CHECKED); \
194 } else if (___rttq_nesting && ___rttq_nesting != INT_MIN && \
195 !READ_ONCE((t)->trc_reader_special.b.blocked)) { \
196 rcu_tasks_trace_qs_blkd(t); \
200 # define rcu_tasks_trace_qs(t) do { } while (0)
203 #define rcu_tasks_qs(t, preempt) \
205 rcu_tasks_classic_qs((t), (preempt)); \
206 rcu_tasks_trace_qs(t); \
209 # ifdef CONFIG_TASKS_RUDE_RCU
210 void call_rcu_tasks_rude(struct rcu_head *head, rcu_callback_t func);
211 void synchronize_rcu_tasks_rude(void);
214 #define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t, false)
215 void exit_tasks_rcu_start(void);
216 void exit_tasks_rcu_stop(void);
217 void exit_tasks_rcu_finish(void);
218 #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
219 #define rcu_tasks_classic_qs(t, preempt) do { } while (0)
220 #define rcu_tasks_qs(t, preempt) do { } while (0)
221 #define rcu_note_voluntary_context_switch(t) do { } while (0)
222 #define call_rcu_tasks call_rcu
223 #define synchronize_rcu_tasks synchronize_rcu
224 static inline void exit_tasks_rcu_start(void) { }
225 static inline void exit_tasks_rcu_stop(void) { }
226 static inline void exit_tasks_rcu_finish(void) { }
227 #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */
230 * rcu_trace_implies_rcu_gp - does an RCU Tasks Trace grace period imply an RCU grace period?
232 * As an accident of implementation, an RCU Tasks Trace grace period also
233 * acts as an RCU grace period. However, this could change at any time.
234 * Code relying on this accident must call this function to verify that
235 * this accident is still happening.
237 * You have been warned!
239 static inline bool rcu_trace_implies_rcu_gp(void) { return true; }
242 * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU
244 * This macro resembles cond_resched(), except that it is defined to
245 * report potential quiescent states to RCU-tasks even if the cond_resched()
246 * machinery were to be shut off, as some advocate for PREEMPTION kernels.
248 #define cond_resched_tasks_rcu_qs() \
250 rcu_tasks_qs(current, false); \
255 * Infrastructure to implement the synchronize_() primitives in
256 * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
259 #if defined(CONFIG_TREE_RCU)
260 #include <linux/rcutree.h>
261 #elif defined(CONFIG_TINY_RCU)
262 #include <linux/rcutiny.h>
264 #error "Unknown RCU implementation specified to kernel configuration"
268 * The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls
269 * are needed for dynamic initialization and destruction of rcu_head
270 * on the stack, and init_rcu_head()/destroy_rcu_head() are needed for
271 * dynamic initialization and destruction of statically allocated rcu_head
272 * structures. However, rcu_head structures allocated dynamically in the
273 * heap don't need any initialization.
275 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
276 void init_rcu_head(struct rcu_head *head);
277 void destroy_rcu_head(struct rcu_head *head);
278 void init_rcu_head_on_stack(struct rcu_head *head);
279 void destroy_rcu_head_on_stack(struct rcu_head *head);
280 #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
281 static inline void init_rcu_head(struct rcu_head *head) { }
282 static inline void destroy_rcu_head(struct rcu_head *head) { }
283 static inline void init_rcu_head_on_stack(struct rcu_head *head) { }
284 static inline void destroy_rcu_head_on_stack(struct rcu_head *head) { }
285 #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
287 #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
288 bool rcu_lockdep_current_cpu_online(void);
289 #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
290 static inline bool rcu_lockdep_current_cpu_online(void) { return true; }
291 #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
293 extern struct lockdep_map rcu_lock_map;
294 extern struct lockdep_map rcu_bh_lock_map;
295 extern struct lockdep_map rcu_sched_lock_map;
296 extern struct lockdep_map rcu_callback_map;
298 #ifdef CONFIG_DEBUG_LOCK_ALLOC
300 static inline void rcu_lock_acquire(struct lockdep_map *map)
302 lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
305 static inline void rcu_lock_release(struct lockdep_map *map)
307 lock_release(map, _THIS_IP_);
310 int debug_lockdep_rcu_enabled(void);
311 int rcu_read_lock_held(void);
312 int rcu_read_lock_bh_held(void);
313 int rcu_read_lock_sched_held(void);
314 int rcu_read_lock_any_held(void);
316 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
318 # define rcu_lock_acquire(a) do { } while (0)
319 # define rcu_lock_release(a) do { } while (0)
321 static inline int rcu_read_lock_held(void)
326 static inline int rcu_read_lock_bh_held(void)
331 static inline int rcu_read_lock_sched_held(void)
333 return !preemptible();
336 static inline int rcu_read_lock_any_held(void)
338 return !preemptible();
341 static inline int debug_lockdep_rcu_enabled(void)
346 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
348 #ifdef CONFIG_PROVE_RCU
351 * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met
352 * @c: condition to check
353 * @s: informative message
355 * This checks debug_lockdep_rcu_enabled() before checking (c) to
356 * prevent early boot splats due to lockdep not yet being initialized,
357 * and rechecks it after checking (c) to prevent false-positive splats
358 * due to races with lockdep being disabled. See commit 3066820034b5dd
359 * ("rcu: Reject RCU_LOCKDEP_WARN() false positives") for more detail.
361 #define RCU_LOCKDEP_WARN(c, s) \
363 static bool __section(".data.unlikely") __warned; \
364 if (debug_lockdep_rcu_enabled() && (c) && \
365 debug_lockdep_rcu_enabled() && !__warned) { \
367 lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
371 #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
372 static inline void rcu_preempt_sleep_check(void)
374 RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
375 "Illegal context switch in RCU read-side critical section");
377 #else /* #ifdef CONFIG_PROVE_RCU */
378 static inline void rcu_preempt_sleep_check(void) { }
379 #endif /* #else #ifdef CONFIG_PROVE_RCU */
381 #define rcu_sleep_check() \
383 rcu_preempt_sleep_check(); \
384 if (!IS_ENABLED(CONFIG_PREEMPT_RT)) \
385 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map), \
386 "Illegal context switch in RCU-bh read-side critical section"); \
387 RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), \
388 "Illegal context switch in RCU-sched read-side critical section"); \
391 #else /* #ifdef CONFIG_PROVE_RCU */
393 #define RCU_LOCKDEP_WARN(c, s) do { } while (0 && (c))
394 #define rcu_sleep_check() do { } while (0)
396 #endif /* #else #ifdef CONFIG_PROVE_RCU */
399 * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
400 * and rcu_assign_pointer(). Some of these could be folded into their
401 * callers, but they are left separate in order to ease introduction of
402 * multiple pointers markings to match different RCU implementations
403 * (e.g., __srcu), should this make sense in the future.
407 #define rcu_check_sparse(p, space) \
408 ((void)(((typeof(*p) space *)p) == p))
409 #else /* #ifdef __CHECKER__ */
410 #define rcu_check_sparse(p, space)
411 #endif /* #else #ifdef __CHECKER__ */
413 #define __unrcu_pointer(p, local) \
415 typeof(*p) *local = (typeof(*p) *__force)(p); \
416 rcu_check_sparse(p, __rcu); \
417 ((typeof(*p) __force __kernel *)(local)); \
420 * unrcu_pointer - mark a pointer as not being RCU protected
421 * @p: pointer needing to lose its __rcu property
423 * Converts @p from an __rcu pointer to a __kernel pointer.
424 * This allows an __rcu pointer to be used with xchg() and friends.
426 #define unrcu_pointer(p) __unrcu_pointer(p, __UNIQUE_ID(rcu))
428 #define __rcu_access_pointer(p, local, space) \
430 typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \
431 rcu_check_sparse(p, space); \
432 ((typeof(*p) __force __kernel *)(local)); \
434 #define __rcu_dereference_check(p, local, c, space) \
436 /* Dependency order vs. p above. */ \
437 typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \
438 RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
439 rcu_check_sparse(p, space); \
440 ((typeof(*p) __force __kernel *)(local)); \
442 #define __rcu_dereference_protected(p, local, c, space) \
444 RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
445 rcu_check_sparse(p, space); \
446 ((typeof(*p) __force __kernel *)(p)); \
448 #define __rcu_dereference_raw(p, local) \
450 /* Dependency order vs. p above. */ \
451 typeof(p) local = READ_ONCE(p); \
452 ((typeof(*p) __force __kernel *)(local)); \
454 #define rcu_dereference_raw(p) __rcu_dereference_raw(p, __UNIQUE_ID(rcu))
457 * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
458 * @v: The value to statically initialize with.
460 #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
463 * rcu_assign_pointer() - assign to RCU-protected pointer
464 * @p: pointer to assign to
465 * @v: value to assign (publish)
467 * Assigns the specified value to the specified RCU-protected
468 * pointer, ensuring that any concurrent RCU readers will see
469 * any prior initialization.
471 * Inserts memory barriers on architectures that require them
472 * (which is most of them), and also prevents the compiler from
473 * reordering the code that initializes the structure after the pointer
474 * assignment. More importantly, this call documents which pointers
475 * will be dereferenced by RCU read-side code.
477 * In some special cases, you may use RCU_INIT_POINTER() instead
478 * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due
479 * to the fact that it does not constrain either the CPU or the compiler.
480 * That said, using RCU_INIT_POINTER() when you should have used
481 * rcu_assign_pointer() is a very bad thing that results in
482 * impossible-to-diagnose memory corruption. So please be careful.
483 * See the RCU_INIT_POINTER() comment header for details.
485 * Note that rcu_assign_pointer() evaluates each of its arguments only
486 * once, appearances notwithstanding. One of the "extra" evaluations
487 * is in typeof() and the other visible only to sparse (__CHECKER__),
488 * neither of which actually execute the argument. As with most cpp
489 * macros, this execute-arguments-only-once property is important, so
490 * please be careful when making changes to rcu_assign_pointer() and the
491 * other macros that it invokes.
493 #define rcu_assign_pointer(p, v) \
495 uintptr_t _r_a_p__v = (uintptr_t)(v); \
496 rcu_check_sparse(p, __rcu); \
498 if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \
499 WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \
501 smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \
505 * rcu_replace_pointer() - replace an RCU pointer, returning its old value
506 * @rcu_ptr: RCU pointer, whose old value is returned
507 * @ptr: regular pointer
508 * @c: the lockdep conditions under which the dereference will take place
510 * Perform a replacement, where @rcu_ptr is an RCU-annotated
511 * pointer and @c is the lockdep argument that is passed to the
512 * rcu_dereference_protected() call used to read that pointer. The old
513 * value of @rcu_ptr is returned, and @rcu_ptr is set to @ptr.
515 #define rcu_replace_pointer(rcu_ptr, ptr, c) \
517 typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c)); \
518 rcu_assign_pointer((rcu_ptr), (ptr)); \
523 * rcu_access_pointer() - fetch RCU pointer with no dereferencing
524 * @p: The pointer to read
526 * Return the value of the specified RCU-protected pointer, but omit the
527 * lockdep checks for being in an RCU read-side critical section. This is
528 * useful when the value of this pointer is accessed, but the pointer is
529 * not dereferenced, for example, when testing an RCU-protected pointer
530 * against NULL. Although rcu_access_pointer() may also be used in cases
531 * where update-side locks prevent the value of the pointer from changing,
532 * you should instead use rcu_dereference_protected() for this use case.
533 * Within an RCU read-side critical section, there is little reason to
534 * use rcu_access_pointer().
536 * It is usually best to test the rcu_access_pointer() return value
537 * directly in order to avoid accidental dereferences being introduced
538 * by later inattentive changes. In other words, assigning the
539 * rcu_access_pointer() return value to a local variable results in an
540 * accident waiting to happen.
542 * It is also permissible to use rcu_access_pointer() when read-side
543 * access to the pointer was removed at least one grace period ago, as is
544 * the case in the context of the RCU callback that is freeing up the data,
545 * or after a synchronize_rcu() returns. This can be useful when tearing
546 * down multi-linked structures after a grace period has elapsed. However,
547 * rcu_dereference_protected() is normally preferred for this use case.
549 #define rcu_access_pointer(p) __rcu_access_pointer((p), __UNIQUE_ID(rcu), __rcu)
552 * rcu_dereference_check() - rcu_dereference with debug checking
553 * @p: The pointer to read, prior to dereferencing
554 * @c: The conditions under which the dereference will take place
556 * Do an rcu_dereference(), but check that the conditions under which the
557 * dereference will take place are correct. Typically the conditions
558 * indicate the various locking conditions that should be held at that
559 * point. The check should return true if the conditions are satisfied.
560 * An implicit check for being in an RCU read-side critical section
561 * (rcu_read_lock()) is included.
565 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
567 * could be used to indicate to lockdep that foo->bar may only be dereferenced
568 * if either rcu_read_lock() is held, or that the lock required to replace
569 * the bar struct at foo->bar is held.
571 * Note that the list of conditions may also include indications of when a lock
572 * need not be held, for example during initialisation or destruction of the
575 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
576 * atomic_read(&foo->usage) == 0);
578 * Inserts memory barriers on architectures that require them
579 * (currently only the Alpha), prevents the compiler from refetching
580 * (and from merging fetches), and, more importantly, documents exactly
581 * which pointers are protected by RCU and checks that the pointer is
582 * annotated as __rcu.
584 #define rcu_dereference_check(p, c) \
585 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
586 (c) || rcu_read_lock_held(), __rcu)
589 * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
590 * @p: The pointer to read, prior to dereferencing
591 * @c: The conditions under which the dereference will take place
593 * This is the RCU-bh counterpart to rcu_dereference_check(). However,
594 * please note that starting in v5.0 kernels, vanilla RCU grace periods
595 * wait for local_bh_disable() regions of code in addition to regions of
596 * code demarked by rcu_read_lock() and rcu_read_unlock(). This means
597 * that synchronize_rcu(), call_rcu, and friends all take not only
598 * rcu_read_lock() but also rcu_read_lock_bh() into account.
600 #define rcu_dereference_bh_check(p, c) \
601 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
602 (c) || rcu_read_lock_bh_held(), __rcu)
605 * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
606 * @p: The pointer to read, prior to dereferencing
607 * @c: The conditions under which the dereference will take place
609 * This is the RCU-sched counterpart to rcu_dereference_check().
610 * However, please note that starting in v5.0 kernels, vanilla RCU grace
611 * periods wait for preempt_disable() regions of code in addition to
612 * regions of code demarked by rcu_read_lock() and rcu_read_unlock().
613 * This means that synchronize_rcu(), call_rcu, and friends all take not
614 * only rcu_read_lock() but also rcu_read_lock_sched() into account.
616 #define rcu_dereference_sched_check(p, c) \
617 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
618 (c) || rcu_read_lock_sched_held(), \
622 * The tracing infrastructure traces RCU (we want that), but unfortunately
623 * some of the RCU checks causes tracing to lock up the system.
625 * The no-tracing version of rcu_dereference_raw() must not call
626 * rcu_read_lock_held().
628 #define rcu_dereference_raw_check(p) \
629 __rcu_dereference_check((p), __UNIQUE_ID(rcu), 1, __rcu)
632 * rcu_dereference_protected() - fetch RCU pointer when updates prevented
633 * @p: The pointer to read, prior to dereferencing
634 * @c: The conditions under which the dereference will take place
636 * Return the value of the specified RCU-protected pointer, but omit
637 * the READ_ONCE(). This is useful in cases where update-side locks
638 * prevent the value of the pointer from changing. Please note that this
639 * primitive does *not* prevent the compiler from repeating this reference
640 * or combining it with other references, so it should not be used without
641 * protection of appropriate locks.
643 * This function is only for update-side use. Using this function
644 * when protected only by rcu_read_lock() will result in infrequent
645 * but very ugly failures.
647 #define rcu_dereference_protected(p, c) \
648 __rcu_dereference_protected((p), __UNIQUE_ID(rcu), (c), __rcu)
652 * rcu_dereference() - fetch RCU-protected pointer for dereferencing
653 * @p: The pointer to read, prior to dereferencing
655 * This is a simple wrapper around rcu_dereference_check().
657 #define rcu_dereference(p) rcu_dereference_check(p, 0)
660 * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
661 * @p: The pointer to read, prior to dereferencing
663 * Makes rcu_dereference_check() do the dirty work.
665 #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
668 * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
669 * @p: The pointer to read, prior to dereferencing
671 * Makes rcu_dereference_check() do the dirty work.
673 #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
676 * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism
677 * @p: The pointer to hand off
679 * This is simply an identity function, but it documents where a pointer
680 * is handed off from RCU to some other synchronization mechanism, for
681 * example, reference counting or locking. In C11, it would map to
682 * kill_dependency(). It could be used as follows::
685 * p = rcu_dereference(gp);
686 * long_lived = is_long_lived(p);
688 * if (!atomic_inc_not_zero(p->refcnt))
689 * long_lived = false;
691 * p = rcu_pointer_handoff(p);
695 #define rcu_pointer_handoff(p) (p)
698 * rcu_read_lock() - mark the beginning of an RCU read-side critical section
700 * When synchronize_rcu() is invoked on one CPU while other CPUs
701 * are within RCU read-side critical sections, then the
702 * synchronize_rcu() is guaranteed to block until after all the other
703 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
704 * on one CPU while other CPUs are within RCU read-side critical
705 * sections, invocation of the corresponding RCU callback is deferred
706 * until after the all the other CPUs exit their critical sections.
708 * In v5.0 and later kernels, synchronize_rcu() and call_rcu() also
709 * wait for regions of code with preemption disabled, including regions of
710 * code with interrupts or softirqs disabled. In pre-v5.0 kernels, which
711 * define synchronize_sched(), only code enclosed within rcu_read_lock()
712 * and rcu_read_unlock() are guaranteed to be waited for.
714 * Note, however, that RCU callbacks are permitted to run concurrently
715 * with new RCU read-side critical sections. One way that this can happen
716 * is via the following sequence of events: (1) CPU 0 enters an RCU
717 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
718 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
719 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
720 * callback is invoked. This is legal, because the RCU read-side critical
721 * section that was running concurrently with the call_rcu() (and which
722 * therefore might be referencing something that the corresponding RCU
723 * callback would free up) has completed before the corresponding
724 * RCU callback is invoked.
726 * RCU read-side critical sections may be nested. Any deferred actions
727 * will be deferred until the outermost RCU read-side critical section
730 * You can avoid reading and understanding the next paragraph by
731 * following this rule: don't put anything in an rcu_read_lock() RCU
732 * read-side critical section that would block in a !PREEMPTION kernel.
733 * But if you want the full story, read on!
735 * In non-preemptible RCU implementations (pure TREE_RCU and TINY_RCU),
736 * it is illegal to block while in an RCU read-side critical section.
737 * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPTION
738 * kernel builds, RCU read-side critical sections may be preempted,
739 * but explicit blocking is illegal. Finally, in preemptible RCU
740 * implementations in real-time (with -rt patchset) kernel builds, RCU
741 * read-side critical sections may be preempted and they may also block, but
742 * only when acquiring spinlocks that are subject to priority inheritance.
744 static __always_inline void rcu_read_lock(void)
748 rcu_lock_acquire(&rcu_lock_map);
749 RCU_LOCKDEP_WARN(!rcu_is_watching(),
750 "rcu_read_lock() used illegally while idle");
754 * So where is rcu_write_lock()? It does not exist, as there is no
755 * way for writers to lock out RCU readers. This is a feature, not
756 * a bug -- this property is what provides RCU's performance benefits.
757 * Of course, writers must coordinate with each other. The normal
758 * spinlock primitives work well for this, but any other technique may be
759 * used as well. RCU does not care how the writers keep out of each
760 * others' way, as long as they do so.
764 * rcu_read_unlock() - marks the end of an RCU read-side critical section.
766 * In almost all situations, rcu_read_unlock() is immune from deadlock.
767 * In recent kernels that have consolidated synchronize_sched() and
768 * synchronize_rcu_bh() into synchronize_rcu(), this deadlock immunity
769 * also extends to the scheduler's runqueue and priority-inheritance
770 * spinlocks, courtesy of the quiescent-state deferral that is carried
771 * out when rcu_read_unlock() is invoked with interrupts disabled.
773 * See rcu_read_lock() for more information.
775 static inline void rcu_read_unlock(void)
777 RCU_LOCKDEP_WARN(!rcu_is_watching(),
778 "rcu_read_unlock() used illegally while idle");
781 rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
785 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
787 * This is equivalent to rcu_read_lock(), but also disables softirqs.
788 * Note that anything else that disables softirqs can also serve as an RCU
789 * read-side critical section. However, please note that this equivalence
790 * applies only to v5.0 and later. Before v5.0, rcu_read_lock() and
791 * rcu_read_lock_bh() were unrelated.
793 * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
794 * must occur in the same context, for example, it is illegal to invoke
795 * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
796 * was invoked from some other task.
798 static inline void rcu_read_lock_bh(void)
802 rcu_lock_acquire(&rcu_bh_lock_map);
803 RCU_LOCKDEP_WARN(!rcu_is_watching(),
804 "rcu_read_lock_bh() used illegally while idle");
808 * rcu_read_unlock_bh() - marks the end of a softirq-only RCU critical section
810 * See rcu_read_lock_bh() for more information.
812 static inline void rcu_read_unlock_bh(void)
814 RCU_LOCKDEP_WARN(!rcu_is_watching(),
815 "rcu_read_unlock_bh() used illegally while idle");
816 rcu_lock_release(&rcu_bh_lock_map);
822 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
824 * This is equivalent to rcu_read_lock(), but also disables preemption.
825 * Read-side critical sections can also be introduced by anything else that
826 * disables preemption, including local_irq_disable() and friends. However,
827 * please note that the equivalence to rcu_read_lock() applies only to
828 * v5.0 and later. Before v5.0, rcu_read_lock() and rcu_read_lock_sched()
831 * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
832 * must occur in the same context, for example, it is illegal to invoke
833 * rcu_read_unlock_sched() from process context if the matching
834 * rcu_read_lock_sched() was invoked from an NMI handler.
836 static inline void rcu_read_lock_sched(void)
839 __acquire(RCU_SCHED);
840 rcu_lock_acquire(&rcu_sched_lock_map);
841 RCU_LOCKDEP_WARN(!rcu_is_watching(),
842 "rcu_read_lock_sched() used illegally while idle");
845 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
846 static inline notrace void rcu_read_lock_sched_notrace(void)
848 preempt_disable_notrace();
849 __acquire(RCU_SCHED);
853 * rcu_read_unlock_sched() - marks the end of a RCU-classic critical section
855 * See rcu_read_lock_sched() for more information.
857 static inline void rcu_read_unlock_sched(void)
859 RCU_LOCKDEP_WARN(!rcu_is_watching(),
860 "rcu_read_unlock_sched() used illegally while idle");
861 rcu_lock_release(&rcu_sched_lock_map);
862 __release(RCU_SCHED);
866 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
867 static inline notrace void rcu_read_unlock_sched_notrace(void)
869 __release(RCU_SCHED);
870 preempt_enable_notrace();
874 * RCU_INIT_POINTER() - initialize an RCU protected pointer
875 * @p: The pointer to be initialized.
876 * @v: The value to initialized the pointer to.
878 * Initialize an RCU-protected pointer in special cases where readers
879 * do not need ordering constraints on the CPU or the compiler. These
882 * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer *or*
883 * 2. The caller has taken whatever steps are required to prevent
884 * RCU readers from concurrently accessing this pointer *or*
885 * 3. The referenced data structure has already been exposed to
886 * readers either at compile time or via rcu_assign_pointer() *and*
888 * a. You have not made *any* reader-visible changes to
889 * this structure since then *or*
890 * b. It is OK for readers accessing this structure from its
891 * new location to see the old state of the structure. (For
892 * example, the changes were to statistical counters or to
893 * other state where exact synchronization is not required.)
895 * Failure to follow these rules governing use of RCU_INIT_POINTER() will
896 * result in impossible-to-diagnose memory corruption. As in the structures
897 * will look OK in crash dumps, but any concurrent RCU readers might
898 * see pre-initialized values of the referenced data structure. So
899 * please be very careful how you use RCU_INIT_POINTER()!!!
901 * If you are creating an RCU-protected linked structure that is accessed
902 * by a single external-to-structure RCU-protected pointer, then you may
903 * use RCU_INIT_POINTER() to initialize the internal RCU-protected
904 * pointers, but you must use rcu_assign_pointer() to initialize the
905 * external-to-structure pointer *after* you have completely initialized
906 * the reader-accessible portions of the linked structure.
908 * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
909 * ordering guarantees for either the CPU or the compiler.
911 #define RCU_INIT_POINTER(p, v) \
913 rcu_check_sparse(p, __rcu); \
914 WRITE_ONCE(p, RCU_INITIALIZER(v)); \
918 * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
919 * @p: The pointer to be initialized.
920 * @v: The value to initialized the pointer to.
922 * GCC-style initialization for an RCU-protected pointer in a structure field.
924 #define RCU_POINTER_INITIALIZER(p, v) \
925 .p = RCU_INITIALIZER(v)
928 * Does the specified offset indicate that the corresponding rcu_head
929 * structure can be handled by kvfree_rcu()?
931 #define __is_kvfree_rcu_offset(offset) ((offset) < 4096)
934 * kfree_rcu() - kfree an object after a grace period.
935 * @ptr: pointer to kfree for double-argument invocations.
936 * @rhf: the name of the struct rcu_head within the type of @ptr.
938 * Many rcu callbacks functions just call kfree() on the base structure.
939 * These functions are trivial, but their size adds up, and furthermore
940 * when they are used in a kernel module, that module must invoke the
941 * high-latency rcu_barrier() function at module-unload time.
943 * The kfree_rcu() function handles this issue. Rather than encoding a
944 * function address in the embedded rcu_head structure, kfree_rcu() instead
945 * encodes the offset of the rcu_head structure within the base structure.
946 * Because the functions are not allowed in the low-order 4096 bytes of
947 * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
948 * If the offset is larger than 4095 bytes, a compile-time error will
949 * be generated in kvfree_rcu_arg_2(). If this error is triggered, you can
950 * either fall back to use of call_rcu() or rearrange the structure to
951 * position the rcu_head structure into the first 4096 bytes.
953 * The object to be freed can be allocated either by kmalloc() or
954 * kmem_cache_alloc().
956 * Note that the allowable offset might decrease in the future.
958 * The BUILD_BUG_ON check must not involve any function calls, hence the
959 * checks are done in macros here.
961 #define kfree_rcu(ptr, rhf) kvfree_rcu_arg_2(ptr, rhf)
962 #define kvfree_rcu(ptr, rhf) kvfree_rcu_arg_2(ptr, rhf)
965 * kfree_rcu_mightsleep() - kfree an object after a grace period.
966 * @ptr: pointer to kfree for single-argument invocations.
968 * When it comes to head-less variant, only one argument
969 * is passed and that is just a pointer which has to be
970 * freed after a grace period. Therefore the semantic is
972 * kfree_rcu_mightsleep(ptr);
974 * where @ptr is the pointer to be freed by kvfree().
976 * Please note, head-less way of freeing is permitted to
977 * use from a context that has to follow might_sleep()
978 * annotation. Otherwise, please switch and embed the
979 * rcu_head structure within the type of @ptr.
981 #define kfree_rcu_mightsleep(ptr) kvfree_rcu_arg_1(ptr)
982 #define kvfree_rcu_mightsleep(ptr) kvfree_rcu_arg_1(ptr)
984 #define kvfree_rcu_arg_2(ptr, rhf) \
986 typeof (ptr) ___p = (ptr); \
989 BUILD_BUG_ON(!__is_kvfree_rcu_offset(offsetof(typeof(*(ptr)), rhf))); \
990 kvfree_call_rcu(&((___p)->rhf), (void *) (___p)); \
994 #define kvfree_rcu_arg_1(ptr) \
996 typeof(ptr) ___p = (ptr); \
999 kvfree_call_rcu(NULL, (void *) (___p)); \
1003 * Place this after a lock-acquisition primitive to guarantee that
1004 * an UNLOCK+LOCK pair acts as a full barrier. This guarantee applies
1005 * if the UNLOCK and LOCK are executed by the same CPU or if the
1006 * UNLOCK and LOCK operate on the same lock variable.
1008 #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE
1009 #define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */
1010 #else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
1011 #define smp_mb__after_unlock_lock() do { } while (0)
1012 #endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
1015 /* Has the specified rcu_head structure been handed to call_rcu()? */
1018 * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu()
1019 * @rhp: The rcu_head structure to initialize.
1021 * If you intend to invoke rcu_head_after_call_rcu() to test whether a
1022 * given rcu_head structure has already been passed to call_rcu(), then
1023 * you must also invoke this rcu_head_init() function on it just after
1024 * allocating that structure. Calls to this function must not race with
1025 * calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation.
1027 static inline void rcu_head_init(struct rcu_head *rhp)
1029 rhp->func = (rcu_callback_t)~0L;
1033 * rcu_head_after_call_rcu() - Has this rcu_head been passed to call_rcu()?
1034 * @rhp: The rcu_head structure to test.
1035 * @f: The function passed to call_rcu() along with @rhp.
1037 * Returns @true if the @rhp has been passed to call_rcu() with @func,
1038 * and @false otherwise. Emits a warning in any other case, including
1039 * the case where @rhp has already been invoked after a grace period.
1040 * Calls to this function must not race with callback invocation. One way
1041 * to avoid such races is to enclose the call to rcu_head_after_call_rcu()
1042 * in an RCU read-side critical section that includes a read-side fetch
1043 * of the pointer to the structure containing @rhp.
1046 rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f)
1048 rcu_callback_t func = READ_ONCE(rhp->func);
1052 WARN_ON_ONCE(func != (rcu_callback_t)~0L);
1056 /* kernel/ksysfs.c definitions */
1057 extern int rcu_expedited;
1058 extern int rcu_normal;
1060 #endif /* __LINUX_RCUPDATE_H */