1 /* SPDX-License-Identifier: GPL-2.0+ */
2 /*
3  * Read-Copy Update mechanism for mutual exclusion
4  *
5  * Copyright IBM Corporation, 2001
6  *
7  * Author: Dipankar Sarma <dipankar@in.ibm.com>
8  *
9  * Based on the original work by Paul McKenney <paulmck@vnet.ibm.com>
10  * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
11  * Papers:
12  * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
13  * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
14  *
15  * For detailed explanation of Read-Copy Update mechanism see -
16  *		http://lse.sourceforge.net/locking/rcupdate.html
17  *
18  */
19 
20 #ifndef __LINUX_RCUPDATE_H
21 #define __LINUX_RCUPDATE_H
22 
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>
33 
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)))
39 
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);
45 
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);
49 
50 // Maximum number of unsigned long values corresponding to
51 // not-yet-completed RCU grace periods.
52 #define NUM_ACTIVE_RCU_POLL_OLDSTATE 2
53 
54 /**
55  * same_state_synchronize_rcu - Are two old-state values identical?
56  * @oldstate1: First old-state value.
57  * @oldstate2: Second old-state value.
58  *
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.
65  */
same_state_synchronize_rcu(unsigned long oldstate1,unsigned long oldstate2)66 static inline bool same_state_synchronize_rcu(unsigned long oldstate1, unsigned long oldstate2)
67 {
68 	return oldstate1 == oldstate2;
69 }
70 
71 #ifdef CONFIG_PREEMPT_RCU
72 
73 void __rcu_read_lock(void);
74 void __rcu_read_unlock(void);
75 
76 /*
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.
81  */
82 #define rcu_preempt_depth() READ_ONCE(current->rcu_read_lock_nesting)
83 
84 #else /* #ifdef CONFIG_PREEMPT_RCU */
85 
86 #ifdef CONFIG_TINY_RCU
87 #define rcu_read_unlock_strict() do { } while (0)
88 #else
89 void rcu_read_unlock_strict(void);
90 #endif
91 
__rcu_read_lock(void)92 static inline void __rcu_read_lock(void)
93 {
94 	preempt_disable();
95 }
96 
__rcu_read_unlock(void)97 static inline void __rcu_read_unlock(void)
98 {
99 	preempt_enable();
100 	if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
101 		rcu_read_unlock_strict();
102 }
103 
rcu_preempt_depth(void)104 static inline int rcu_preempt_depth(void)
105 {
106 	return 0;
107 }
108 
109 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
110 
111 #ifdef CONFIG_RCU_LAZY
112 void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func);
113 #else
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)
115 {
116 	call_rcu(head, func);
117 }
118 #endif
119 
120 /* Internal to kernel */
121 void rcu_init(void);
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);
126 
127 #ifdef CONFIG_TASKS_RCU_GENERIC
128 void rcu_init_tasks_generic(void);
129 #else
rcu_init_tasks_generic(void)130 static inline void rcu_init_tasks_generic(void) { }
131 #endif
132 
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 */
rcu_sysrq_start(void)137 static inline void rcu_sysrq_start(void) { }
rcu_sysrq_end(void)138 static inline void rcu_sysrq_end(void) { }
139 #endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
140 
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);
143 #else
rcu_irq_work_resched(void)144 static inline void rcu_irq_work_resched(void) { }
145 #endif
146 
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 */
rcu_init_nohz(void)153 static inline void rcu_init_nohz(void) { }
rcu_nocb_cpu_offload(int cpu)154 static inline int rcu_nocb_cpu_offload(int cpu) { return -EINVAL; }
rcu_nocb_cpu_deoffload(int cpu)155 static inline int rcu_nocb_cpu_deoffload(int cpu) { return 0; }
rcu_nocb_flush_deferred_wakeup(void)156 static inline void rcu_nocb_flush_deferred_wakeup(void) { }
157 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
158 
159 /**
160  * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
161  * @a: Code that RCU needs to pay attention to.
162  *
163  * RCU read-side critical sections are forbidden in the inner idle loop,
164  * that is, between the ct_idle_enter() and the ct_idle_exit() -- RCU
165  * will happily ignore any such read-side critical sections.  However,
166  * things like powertop need tracepoints in the inner idle loop.
167  *
168  * This macro provides the way out:  RCU_NONIDLE(do_something_with_RCU())
169  * will tell RCU that it needs to pay attention, invoke its argument
170  * (in this example, calling the do_something_with_RCU() function),
171  * and then tell RCU to go back to ignoring this CPU.  It is permissible
172  * to nest RCU_NONIDLE() wrappers, but not indefinitely (but the limit is
173  * on the order of a million or so, even on 32-bit systems).  It is
174  * not legal to block within RCU_NONIDLE(), nor is it permissible to
175  * transfer control either into or out of RCU_NONIDLE()'s statement.
176  */
177 #define RCU_NONIDLE(a) \
178 	do { \
179 		ct_irq_enter_irqson(); \
180 		do { a; } while (0); \
181 		ct_irq_exit_irqson(); \
182 	} while (0)
183 
184 /*
185  * Note a quasi-voluntary context switch for RCU-tasks's benefit.
186  * This is a macro rather than an inline function to avoid #include hell.
187  */
188 #ifdef CONFIG_TASKS_RCU_GENERIC
189 
190 # ifdef CONFIG_TASKS_RCU
191 # define rcu_tasks_classic_qs(t, preempt)				\
192 	do {								\
193 		if (!(preempt) && READ_ONCE((t)->rcu_tasks_holdout))	\
194 			WRITE_ONCE((t)->rcu_tasks_holdout, false);	\
195 	} while (0)
196 void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
197 void synchronize_rcu_tasks(void);
198 # else
199 # define rcu_tasks_classic_qs(t, preempt) do { } while (0)
200 # define call_rcu_tasks call_rcu
201 # define synchronize_rcu_tasks synchronize_rcu
202 # endif
203 
204 # ifdef CONFIG_TASKS_TRACE_RCU
205 // Bits for ->trc_reader_special.b.need_qs field.
206 #define TRC_NEED_QS		0x1  // Task needs a quiescent state.
207 #define TRC_NEED_QS_CHECKED	0x2  // Task has been checked for needing quiescent state.
208 
209 u8 rcu_trc_cmpxchg_need_qs(struct task_struct *t, u8 old, u8 new);
210 void rcu_tasks_trace_qs_blkd(struct task_struct *t);
211 
212 # define rcu_tasks_trace_qs(t)							\
213 	do {									\
214 		int ___rttq_nesting = READ_ONCE((t)->trc_reader_nesting);	\
215 										\
216 		if (likely(!READ_ONCE((t)->trc_reader_special.b.need_qs)) &&	\
217 		    likely(!___rttq_nesting)) {					\
218 			rcu_trc_cmpxchg_need_qs((t), 0,	TRC_NEED_QS_CHECKED);	\
219 		} else if (___rttq_nesting && ___rttq_nesting != INT_MIN &&	\
220 			   !READ_ONCE((t)->trc_reader_special.b.blocked)) {	\
221 			rcu_tasks_trace_qs_blkd(t);				\
222 		}								\
223 	} while (0)
224 # else
225 # define rcu_tasks_trace_qs(t) do { } while (0)
226 # endif
227 
228 #define rcu_tasks_qs(t, preempt)					\
229 do {									\
230 	rcu_tasks_classic_qs((t), (preempt));				\
231 	rcu_tasks_trace_qs(t);						\
232 } while (0)
233 
234 # ifdef CONFIG_TASKS_RUDE_RCU
235 void call_rcu_tasks_rude(struct rcu_head *head, rcu_callback_t func);
236 void synchronize_rcu_tasks_rude(void);
237 # endif
238 
239 #define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t, false)
240 void exit_tasks_rcu_start(void);
241 void exit_tasks_rcu_stop(void);
242 void exit_tasks_rcu_finish(void);
243 #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
244 #define rcu_tasks_classic_qs(t, preempt) do { } while (0)
245 #define rcu_tasks_qs(t, preempt) do { } while (0)
246 #define rcu_note_voluntary_context_switch(t) do { } while (0)
247 #define call_rcu_tasks call_rcu
248 #define synchronize_rcu_tasks synchronize_rcu
exit_tasks_rcu_start(void)249 static inline void exit_tasks_rcu_start(void) { }
exit_tasks_rcu_stop(void)250 static inline void exit_tasks_rcu_stop(void) { }
exit_tasks_rcu_finish(void)251 static inline void exit_tasks_rcu_finish(void) { }
252 #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */
253 
254 /**
255  * rcu_trace_implies_rcu_gp - does an RCU Tasks Trace grace period imply an RCU grace period?
256  *
257  * As an accident of implementation, an RCU Tasks Trace grace period also
258  * acts as an RCU grace period.  However, this could change at any time.
259  * Code relying on this accident must call this function to verify that
260  * this accident is still happening.
261  *
262  * You have been warned!
263  */
rcu_trace_implies_rcu_gp(void)264 static inline bool rcu_trace_implies_rcu_gp(void) { return true; }
265 
266 /**
267  * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU
268  *
269  * This macro resembles cond_resched(), except that it is defined to
270  * report potential quiescent states to RCU-tasks even if the cond_resched()
271  * machinery were to be shut off, as some advocate for PREEMPTION kernels.
272  */
273 #define cond_resched_tasks_rcu_qs() \
274 do { \
275 	rcu_tasks_qs(current, false); \
276 	cond_resched(); \
277 } while (0)
278 
279 /*
280  * Infrastructure to implement the synchronize_() primitives in
281  * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
282  */
283 
284 #if defined(CONFIG_TREE_RCU)
285 #include <linux/rcutree.h>
286 #elif defined(CONFIG_TINY_RCU)
287 #include <linux/rcutiny.h>
288 #else
289 #error "Unknown RCU implementation specified to kernel configuration"
290 #endif
291 
292 /*
293  * The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls
294  * are needed for dynamic initialization and destruction of rcu_head
295  * on the stack, and init_rcu_head()/destroy_rcu_head() are needed for
296  * dynamic initialization and destruction of statically allocated rcu_head
297  * structures.  However, rcu_head structures allocated dynamically in the
298  * heap don't need any initialization.
299  */
300 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
301 void init_rcu_head(struct rcu_head *head);
302 void destroy_rcu_head(struct rcu_head *head);
303 void init_rcu_head_on_stack(struct rcu_head *head);
304 void destroy_rcu_head_on_stack(struct rcu_head *head);
305 #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
init_rcu_head(struct rcu_head * head)306 static inline void init_rcu_head(struct rcu_head *head) { }
destroy_rcu_head(struct rcu_head * head)307 static inline void destroy_rcu_head(struct rcu_head *head) { }
init_rcu_head_on_stack(struct rcu_head * head)308 static inline void init_rcu_head_on_stack(struct rcu_head *head) { }
destroy_rcu_head_on_stack(struct rcu_head * head)309 static inline void destroy_rcu_head_on_stack(struct rcu_head *head) { }
310 #endif	/* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
311 
312 #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
313 bool rcu_lockdep_current_cpu_online(void);
314 #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
rcu_lockdep_current_cpu_online(void)315 static inline bool rcu_lockdep_current_cpu_online(void) { return true; }
316 #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
317 
318 extern struct lockdep_map rcu_lock_map;
319 extern struct lockdep_map rcu_bh_lock_map;
320 extern struct lockdep_map rcu_sched_lock_map;
321 extern struct lockdep_map rcu_callback_map;
322 
323 #ifdef CONFIG_DEBUG_LOCK_ALLOC
324 
rcu_lock_acquire(struct lockdep_map * map)325 static inline void rcu_lock_acquire(struct lockdep_map *map)
326 {
327 	lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
328 }
329 
rcu_lock_release(struct lockdep_map * map)330 static inline void rcu_lock_release(struct lockdep_map *map)
331 {
332 	lock_release(map, _THIS_IP_);
333 }
334 
335 int debug_lockdep_rcu_enabled(void);
336 int rcu_read_lock_held(void);
337 int rcu_read_lock_bh_held(void);
338 int rcu_read_lock_sched_held(void);
339 int rcu_read_lock_any_held(void);
340 
341 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
342 
343 # define rcu_lock_acquire(a)		do { } while (0)
344 # define rcu_lock_release(a)		do { } while (0)
345 
rcu_read_lock_held(void)346 static inline int rcu_read_lock_held(void)
347 {
348 	return 1;
349 }
350 
rcu_read_lock_bh_held(void)351 static inline int rcu_read_lock_bh_held(void)
352 {
353 	return 1;
354 }
355 
rcu_read_lock_sched_held(void)356 static inline int rcu_read_lock_sched_held(void)
357 {
358 	return !preemptible();
359 }
360 
rcu_read_lock_any_held(void)361 static inline int rcu_read_lock_any_held(void)
362 {
363 	return !preemptible();
364 }
365 
debug_lockdep_rcu_enabled(void)366 static inline int debug_lockdep_rcu_enabled(void)
367 {
368 	return 0;
369 }
370 
371 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
372 
373 #ifdef CONFIG_PROVE_RCU
374 
375 /**
376  * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met
377  * @c: condition to check
378  * @s: informative message
379  *
380  * This checks debug_lockdep_rcu_enabled() before checking (c) to
381  * prevent early boot splats due to lockdep not yet being initialized,
382  * and rechecks it after checking (c) to prevent false-positive splats
383  * due to races with lockdep being disabled.  See commit 3066820034b5dd
384  * ("rcu: Reject RCU_LOCKDEP_WARN() false positives") for more detail.
385  */
386 #define RCU_LOCKDEP_WARN(c, s)						\
387 	do {								\
388 		static bool __section(".data.unlikely") __warned;	\
389 		if (debug_lockdep_rcu_enabled() && (c) &&		\
390 		    debug_lockdep_rcu_enabled() && !__warned) {		\
391 			__warned = true;				\
392 			lockdep_rcu_suspicious(__FILE__, __LINE__, s);	\
393 		}							\
394 	} while (0)
395 
396 #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
rcu_preempt_sleep_check(void)397 static inline void rcu_preempt_sleep_check(void)
398 {
399 	RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
400 			 "Illegal context switch in RCU read-side critical section");
401 }
402 #else /* #ifdef CONFIG_PROVE_RCU */
rcu_preempt_sleep_check(void)403 static inline void rcu_preempt_sleep_check(void) { }
404 #endif /* #else #ifdef CONFIG_PROVE_RCU */
405 
406 #define rcu_sleep_check()						\
407 	do {								\
408 		rcu_preempt_sleep_check();				\
409 		if (!IS_ENABLED(CONFIG_PREEMPT_RT))			\
410 		    RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map),	\
411 				 "Illegal context switch in RCU-bh read-side critical section"); \
412 		RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map),	\
413 				 "Illegal context switch in RCU-sched read-side critical section"); \
414 	} while (0)
415 
416 #else /* #ifdef CONFIG_PROVE_RCU */
417 
418 #define RCU_LOCKDEP_WARN(c, s) do { } while (0 && (c))
419 #define rcu_sleep_check() do { } while (0)
420 
421 #endif /* #else #ifdef CONFIG_PROVE_RCU */
422 
423 /*
424  * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
425  * and rcu_assign_pointer().  Some of these could be folded into their
426  * callers, but they are left separate in order to ease introduction of
427  * multiple pointers markings to match different RCU implementations
428  * (e.g., __srcu), should this make sense in the future.
429  */
430 
431 #ifdef __CHECKER__
432 #define rcu_check_sparse(p, space) \
433 	((void)(((typeof(*p) space *)p) == p))
434 #else /* #ifdef __CHECKER__ */
435 #define rcu_check_sparse(p, space)
436 #endif /* #else #ifdef __CHECKER__ */
437 
438 #define __unrcu_pointer(p, local)					\
439 ({									\
440 	typeof(*p) *local = (typeof(*p) *__force)(p);			\
441 	rcu_check_sparse(p, __rcu);					\
442 	((typeof(*p) __force __kernel *)(local)); 			\
443 })
444 /**
445  * unrcu_pointer - mark a pointer as not being RCU protected
446  * @p: pointer needing to lose its __rcu property
447  *
448  * Converts @p from an __rcu pointer to a __kernel pointer.
449  * This allows an __rcu pointer to be used with xchg() and friends.
450  */
451 #define unrcu_pointer(p) __unrcu_pointer(p, __UNIQUE_ID(rcu))
452 
453 #define __rcu_access_pointer(p, local, space) \
454 ({ \
455 	typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \
456 	rcu_check_sparse(p, space); \
457 	((typeof(*p) __force __kernel *)(local)); \
458 })
459 #define __rcu_dereference_check(p, local, c, space) \
460 ({ \
461 	/* Dependency order vs. p above. */ \
462 	typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \
463 	RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
464 	rcu_check_sparse(p, space); \
465 	((typeof(*p) __force __kernel *)(local)); \
466 })
467 #define __rcu_dereference_protected(p, local, c, space) \
468 ({ \
469 	RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
470 	rcu_check_sparse(p, space); \
471 	((typeof(*p) __force __kernel *)(p)); \
472 })
473 #define __rcu_dereference_raw(p, local) \
474 ({ \
475 	/* Dependency order vs. p above. */ \
476 	typeof(p) local = READ_ONCE(p); \
477 	((typeof(*p) __force __kernel *)(local)); \
478 })
479 #define rcu_dereference_raw(p) __rcu_dereference_raw(p, __UNIQUE_ID(rcu))
480 
481 /**
482  * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
483  * @v: The value to statically initialize with.
484  */
485 #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
486 
487 /**
488  * rcu_assign_pointer() - assign to RCU-protected pointer
489  * @p: pointer to assign to
490  * @v: value to assign (publish)
491  *
492  * Assigns the specified value to the specified RCU-protected
493  * pointer, ensuring that any concurrent RCU readers will see
494  * any prior initialization.
495  *
496  * Inserts memory barriers on architectures that require them
497  * (which is most of them), and also prevents the compiler from
498  * reordering the code that initializes the structure after the pointer
499  * assignment.  More importantly, this call documents which pointers
500  * will be dereferenced by RCU read-side code.
501  *
502  * In some special cases, you may use RCU_INIT_POINTER() instead
503  * of rcu_assign_pointer().  RCU_INIT_POINTER() is a bit faster due
504  * to the fact that it does not constrain either the CPU or the compiler.
505  * That said, using RCU_INIT_POINTER() when you should have used
506  * rcu_assign_pointer() is a very bad thing that results in
507  * impossible-to-diagnose memory corruption.  So please be careful.
508  * See the RCU_INIT_POINTER() comment header for details.
509  *
510  * Note that rcu_assign_pointer() evaluates each of its arguments only
511  * once, appearances notwithstanding.  One of the "extra" evaluations
512  * is in typeof() and the other visible only to sparse (__CHECKER__),
513  * neither of which actually execute the argument.  As with most cpp
514  * macros, this execute-arguments-only-once property is important, so
515  * please be careful when making changes to rcu_assign_pointer() and the
516  * other macros that it invokes.
517  */
518 #define rcu_assign_pointer(p, v)					      \
519 do {									      \
520 	uintptr_t _r_a_p__v = (uintptr_t)(v);				      \
521 	rcu_check_sparse(p, __rcu);					      \
522 									      \
523 	if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL)	      \
524 		WRITE_ONCE((p), (typeof(p))(_r_a_p__v));		      \
525 	else								      \
526 		smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \
527 } while (0)
528 
529 /**
530  * rcu_replace_pointer() - replace an RCU pointer, returning its old value
531  * @rcu_ptr: RCU pointer, whose old value is returned
532  * @ptr: regular pointer
533  * @c: the lockdep conditions under which the dereference will take place
534  *
535  * Perform a replacement, where @rcu_ptr is an RCU-annotated
536  * pointer and @c is the lockdep argument that is passed to the
537  * rcu_dereference_protected() call used to read that pointer.  The old
538  * value of @rcu_ptr is returned, and @rcu_ptr is set to @ptr.
539  */
540 #define rcu_replace_pointer(rcu_ptr, ptr, c)				\
541 ({									\
542 	typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c));	\
543 	rcu_assign_pointer((rcu_ptr), (ptr));				\
544 	__tmp;								\
545 })
546 
547 /**
548  * rcu_access_pointer() - fetch RCU pointer with no dereferencing
549  * @p: The pointer to read
550  *
551  * Return the value of the specified RCU-protected pointer, but omit the
552  * lockdep checks for being in an RCU read-side critical section.  This is
553  * useful when the value of this pointer is accessed, but the pointer is
554  * not dereferenced, for example, when testing an RCU-protected pointer
555  * against NULL.  Although rcu_access_pointer() may also be used in cases
556  * where update-side locks prevent the value of the pointer from changing,
557  * you should instead use rcu_dereference_protected() for this use case.
558  * Within an RCU read-side critical section, there is little reason to
559  * use rcu_access_pointer().
560  *
561  * It is usually best to test the rcu_access_pointer() return value
562  * directly in order to avoid accidental dereferences being introduced
563  * by later inattentive changes.  In other words, assigning the
564  * rcu_access_pointer() return value to a local variable results in an
565  * accident waiting to happen.
566  *
567  * It is also permissible to use rcu_access_pointer() when read-side
568  * access to the pointer was removed at least one grace period ago, as is
569  * the case in the context of the RCU callback that is freeing up the data,
570  * or after a synchronize_rcu() returns.  This can be useful when tearing
571  * down multi-linked structures after a grace period has elapsed.  However,
572  * rcu_dereference_protected() is normally preferred for this use case.
573  */
574 #define rcu_access_pointer(p) __rcu_access_pointer((p), __UNIQUE_ID(rcu), __rcu)
575 
576 /**
577  * rcu_dereference_check() - rcu_dereference with debug checking
578  * @p: The pointer to read, prior to dereferencing
579  * @c: The conditions under which the dereference will take place
580  *
581  * Do an rcu_dereference(), but check that the conditions under which the
582  * dereference will take place are correct.  Typically the conditions
583  * indicate the various locking conditions that should be held at that
584  * point.  The check should return true if the conditions are satisfied.
585  * An implicit check for being in an RCU read-side critical section
586  * (rcu_read_lock()) is included.
587  *
588  * For example:
589  *
590  *	bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
591  *
592  * could be used to indicate to lockdep that foo->bar may only be dereferenced
593  * if either rcu_read_lock() is held, or that the lock required to replace
594  * the bar struct at foo->bar is held.
595  *
596  * Note that the list of conditions may also include indications of when a lock
597  * need not be held, for example during initialisation or destruction of the
598  * target struct:
599  *
600  *	bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
601  *					      atomic_read(&foo->usage) == 0);
602  *
603  * Inserts memory barriers on architectures that require them
604  * (currently only the Alpha), prevents the compiler from refetching
605  * (and from merging fetches), and, more importantly, documents exactly
606  * which pointers are protected by RCU and checks that the pointer is
607  * annotated as __rcu.
608  */
609 #define rcu_dereference_check(p, c) \
610 	__rcu_dereference_check((p), __UNIQUE_ID(rcu), \
611 				(c) || rcu_read_lock_held(), __rcu)
612 
613 /**
614  * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
615  * @p: The pointer to read, prior to dereferencing
616  * @c: The conditions under which the dereference will take place
617  *
618  * This is the RCU-bh counterpart to rcu_dereference_check().  However,
619  * please note that starting in v5.0 kernels, vanilla RCU grace periods
620  * wait for local_bh_disable() regions of code in addition to regions of
621  * code demarked by rcu_read_lock() and rcu_read_unlock().  This means
622  * that synchronize_rcu(), call_rcu, and friends all take not only
623  * rcu_read_lock() but also rcu_read_lock_bh() into account.
624  */
625 #define rcu_dereference_bh_check(p, c) \
626 	__rcu_dereference_check((p), __UNIQUE_ID(rcu), \
627 				(c) || rcu_read_lock_bh_held(), __rcu)
628 
629 /**
630  * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
631  * @p: The pointer to read, prior to dereferencing
632  * @c: The conditions under which the dereference will take place
633  *
634  * This is the RCU-sched counterpart to rcu_dereference_check().
635  * However, please note that starting in v5.0 kernels, vanilla RCU grace
636  * periods wait for preempt_disable() regions of code in addition to
637  * regions of code demarked by rcu_read_lock() and rcu_read_unlock().
638  * This means that synchronize_rcu(), call_rcu, and friends all take not
639  * only rcu_read_lock() but also rcu_read_lock_sched() into account.
640  */
641 #define rcu_dereference_sched_check(p, c) \
642 	__rcu_dereference_check((p), __UNIQUE_ID(rcu), \
643 				(c) || rcu_read_lock_sched_held(), \
644 				__rcu)
645 
646 /*
647  * The tracing infrastructure traces RCU (we want that), but unfortunately
648  * some of the RCU checks causes tracing to lock up the system.
649  *
650  * The no-tracing version of rcu_dereference_raw() must not call
651  * rcu_read_lock_held().
652  */
653 #define rcu_dereference_raw_check(p) \
654 	__rcu_dereference_check((p), __UNIQUE_ID(rcu), 1, __rcu)
655 
656 /**
657  * rcu_dereference_protected() - fetch RCU pointer when updates prevented
658  * @p: The pointer to read, prior to dereferencing
659  * @c: The conditions under which the dereference will take place
660  *
661  * Return the value of the specified RCU-protected pointer, but omit
662  * the READ_ONCE().  This is useful in cases where update-side locks
663  * prevent the value of the pointer from changing.  Please note that this
664  * primitive does *not* prevent the compiler from repeating this reference
665  * or combining it with other references, so it should not be used without
666  * protection of appropriate locks.
667  *
668  * This function is only for update-side use.  Using this function
669  * when protected only by rcu_read_lock() will result in infrequent
670  * but very ugly failures.
671  */
672 #define rcu_dereference_protected(p, c) \
673 	__rcu_dereference_protected((p), __UNIQUE_ID(rcu), (c), __rcu)
674 
675 
676 /**
677  * rcu_dereference() - fetch RCU-protected pointer for dereferencing
678  * @p: The pointer to read, prior to dereferencing
679  *
680  * This is a simple wrapper around rcu_dereference_check().
681  */
682 #define rcu_dereference(p) rcu_dereference_check(p, 0)
683 
684 /**
685  * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
686  * @p: The pointer to read, prior to dereferencing
687  *
688  * Makes rcu_dereference_check() do the dirty work.
689  */
690 #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
691 
692 /**
693  * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
694  * @p: The pointer to read, prior to dereferencing
695  *
696  * Makes rcu_dereference_check() do the dirty work.
697  */
698 #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
699 
700 /**
701  * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism
702  * @p: The pointer to hand off
703  *
704  * This is simply an identity function, but it documents where a pointer
705  * is handed off from RCU to some other synchronization mechanism, for
706  * example, reference counting or locking.  In C11, it would map to
707  * kill_dependency().  It could be used as follows::
708  *
709  *	rcu_read_lock();
710  *	p = rcu_dereference(gp);
711  *	long_lived = is_long_lived(p);
712  *	if (long_lived) {
713  *		if (!atomic_inc_not_zero(p->refcnt))
714  *			long_lived = false;
715  *		else
716  *			p = rcu_pointer_handoff(p);
717  *	}
718  *	rcu_read_unlock();
719  */
720 #define rcu_pointer_handoff(p) (p)
721 
722 /**
723  * rcu_read_lock() - mark the beginning of an RCU read-side critical section
724  *
725  * When synchronize_rcu() is invoked on one CPU while other CPUs
726  * are within RCU read-side critical sections, then the
727  * synchronize_rcu() is guaranteed to block until after all the other
728  * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
729  * on one CPU while other CPUs are within RCU read-side critical
730  * sections, invocation of the corresponding RCU callback is deferred
731  * until after the all the other CPUs exit their critical sections.
732  *
733  * In v5.0 and later kernels, synchronize_rcu() and call_rcu() also
734  * wait for regions of code with preemption disabled, including regions of
735  * code with interrupts or softirqs disabled.  In pre-v5.0 kernels, which
736  * define synchronize_sched(), only code enclosed within rcu_read_lock()
737  * and rcu_read_unlock() are guaranteed to be waited for.
738  *
739  * Note, however, that RCU callbacks are permitted to run concurrently
740  * with new RCU read-side critical sections.  One way that this can happen
741  * is via the following sequence of events: (1) CPU 0 enters an RCU
742  * read-side critical section, (2) CPU 1 invokes call_rcu() to register
743  * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
744  * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
745  * callback is invoked.  This is legal, because the RCU read-side critical
746  * section that was running concurrently with the call_rcu() (and which
747  * therefore might be referencing something that the corresponding RCU
748  * callback would free up) has completed before the corresponding
749  * RCU callback is invoked.
750  *
751  * RCU read-side critical sections may be nested.  Any deferred actions
752  * will be deferred until the outermost RCU read-side critical section
753  * completes.
754  *
755  * You can avoid reading and understanding the next paragraph by
756  * following this rule: don't put anything in an rcu_read_lock() RCU
757  * read-side critical section that would block in a !PREEMPTION kernel.
758  * But if you want the full story, read on!
759  *
760  * In non-preemptible RCU implementations (pure TREE_RCU and TINY_RCU),
761  * it is illegal to block while in an RCU read-side critical section.
762  * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPTION
763  * kernel builds, RCU read-side critical sections may be preempted,
764  * but explicit blocking is illegal.  Finally, in preemptible RCU
765  * implementations in real-time (with -rt patchset) kernel builds, RCU
766  * read-side critical sections may be preempted and they may also block, but
767  * only when acquiring spinlocks that are subject to priority inheritance.
768  */
rcu_read_lock(void)769 static __always_inline void rcu_read_lock(void)
770 {
771 	__rcu_read_lock();
772 	__acquire(RCU);
773 	rcu_lock_acquire(&rcu_lock_map);
774 	RCU_LOCKDEP_WARN(!rcu_is_watching(),
775 			 "rcu_read_lock() used illegally while idle");
776 }
777 
778 /*
779  * So where is rcu_write_lock()?  It does not exist, as there is no
780  * way for writers to lock out RCU readers.  This is a feature, not
781  * a bug -- this property is what provides RCU's performance benefits.
782  * Of course, writers must coordinate with each other.  The normal
783  * spinlock primitives work well for this, but any other technique may be
784  * used as well.  RCU does not care how the writers keep out of each
785  * others' way, as long as they do so.
786  */
787 
788 /**
789  * rcu_read_unlock() - marks the end of an RCU read-side critical section.
790  *
791  * In almost all situations, rcu_read_unlock() is immune from deadlock.
792  * In recent kernels that have consolidated synchronize_sched() and
793  * synchronize_rcu_bh() into synchronize_rcu(), this deadlock immunity
794  * also extends to the scheduler's runqueue and priority-inheritance
795  * spinlocks, courtesy of the quiescent-state deferral that is carried
796  * out when rcu_read_unlock() is invoked with interrupts disabled.
797  *
798  * See rcu_read_lock() for more information.
799  */
rcu_read_unlock(void)800 static inline void rcu_read_unlock(void)
801 {
802 	RCU_LOCKDEP_WARN(!rcu_is_watching(),
803 			 "rcu_read_unlock() used illegally while idle");
804 	__release(RCU);
805 	__rcu_read_unlock();
806 	rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
807 }
808 
809 /**
810  * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
811  *
812  * This is equivalent to rcu_read_lock(), but also disables softirqs.
813  * Note that anything else that disables softirqs can also serve as an RCU
814  * read-side critical section.  However, please note that this equivalence
815  * applies only to v5.0 and later.  Before v5.0, rcu_read_lock() and
816  * rcu_read_lock_bh() were unrelated.
817  *
818  * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
819  * must occur in the same context, for example, it is illegal to invoke
820  * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
821  * was invoked from some other task.
822  */
rcu_read_lock_bh(void)823 static inline void rcu_read_lock_bh(void)
824 {
825 	local_bh_disable();
826 	__acquire(RCU_BH);
827 	rcu_lock_acquire(&rcu_bh_lock_map);
828 	RCU_LOCKDEP_WARN(!rcu_is_watching(),
829 			 "rcu_read_lock_bh() used illegally while idle");
830 }
831 
832 /**
833  * rcu_read_unlock_bh() - marks the end of a softirq-only RCU critical section
834  *
835  * See rcu_read_lock_bh() for more information.
836  */
rcu_read_unlock_bh(void)837 static inline void rcu_read_unlock_bh(void)
838 {
839 	RCU_LOCKDEP_WARN(!rcu_is_watching(),
840 			 "rcu_read_unlock_bh() used illegally while idle");
841 	rcu_lock_release(&rcu_bh_lock_map);
842 	__release(RCU_BH);
843 	local_bh_enable();
844 }
845 
846 /**
847  * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
848  *
849  * This is equivalent to rcu_read_lock(), but also disables preemption.
850  * Read-side critical sections can also be introduced by anything else that
851  * disables preemption, including local_irq_disable() and friends.  However,
852  * please note that the equivalence to rcu_read_lock() applies only to
853  * v5.0 and later.  Before v5.0, rcu_read_lock() and rcu_read_lock_sched()
854  * were unrelated.
855  *
856  * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
857  * must occur in the same context, for example, it is illegal to invoke
858  * rcu_read_unlock_sched() from process context if the matching
859  * rcu_read_lock_sched() was invoked from an NMI handler.
860  */
rcu_read_lock_sched(void)861 static inline void rcu_read_lock_sched(void)
862 {
863 	preempt_disable();
864 	__acquire(RCU_SCHED);
865 	rcu_lock_acquire(&rcu_sched_lock_map);
866 	RCU_LOCKDEP_WARN(!rcu_is_watching(),
867 			 "rcu_read_lock_sched() used illegally while idle");
868 }
869 
870 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
rcu_read_lock_sched_notrace(void)871 static inline notrace void rcu_read_lock_sched_notrace(void)
872 {
873 	preempt_disable_notrace();
874 	__acquire(RCU_SCHED);
875 }
876 
877 /**
878  * rcu_read_unlock_sched() - marks the end of a RCU-classic critical section
879  *
880  * See rcu_read_lock_sched() for more information.
881  */
rcu_read_unlock_sched(void)882 static inline void rcu_read_unlock_sched(void)
883 {
884 	RCU_LOCKDEP_WARN(!rcu_is_watching(),
885 			 "rcu_read_unlock_sched() used illegally while idle");
886 	rcu_lock_release(&rcu_sched_lock_map);
887 	__release(RCU_SCHED);
888 	preempt_enable();
889 }
890 
891 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
rcu_read_unlock_sched_notrace(void)892 static inline notrace void rcu_read_unlock_sched_notrace(void)
893 {
894 	__release(RCU_SCHED);
895 	preempt_enable_notrace();
896 }
897 
898 /**
899  * RCU_INIT_POINTER() - initialize an RCU protected pointer
900  * @p: The pointer to be initialized.
901  * @v: The value to initialized the pointer to.
902  *
903  * Initialize an RCU-protected pointer in special cases where readers
904  * do not need ordering constraints on the CPU or the compiler.  These
905  * special cases are:
906  *
907  * 1.	This use of RCU_INIT_POINTER() is NULLing out the pointer *or*
908  * 2.	The caller has taken whatever steps are required to prevent
909  *	RCU readers from concurrently accessing this pointer *or*
910  * 3.	The referenced data structure has already been exposed to
911  *	readers either at compile time or via rcu_assign_pointer() *and*
912  *
913  *	a.	You have not made *any* reader-visible changes to
914  *		this structure since then *or*
915  *	b.	It is OK for readers accessing this structure from its
916  *		new location to see the old state of the structure.  (For
917  *		example, the changes were to statistical counters or to
918  *		other state where exact synchronization is not required.)
919  *
920  * Failure to follow these rules governing use of RCU_INIT_POINTER() will
921  * result in impossible-to-diagnose memory corruption.  As in the structures
922  * will look OK in crash dumps, but any concurrent RCU readers might
923  * see pre-initialized values of the referenced data structure.  So
924  * please be very careful how you use RCU_INIT_POINTER()!!!
925  *
926  * If you are creating an RCU-protected linked structure that is accessed
927  * by a single external-to-structure RCU-protected pointer, then you may
928  * use RCU_INIT_POINTER() to initialize the internal RCU-protected
929  * pointers, but you must use rcu_assign_pointer() to initialize the
930  * external-to-structure pointer *after* you have completely initialized
931  * the reader-accessible portions of the linked structure.
932  *
933  * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
934  * ordering guarantees for either the CPU or the compiler.
935  */
936 #define RCU_INIT_POINTER(p, v) \
937 	do { \
938 		rcu_check_sparse(p, __rcu); \
939 		WRITE_ONCE(p, RCU_INITIALIZER(v)); \
940 	} while (0)
941 
942 /**
943  * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
944  * @p: The pointer to be initialized.
945  * @v: The value to initialized the pointer to.
946  *
947  * GCC-style initialization for an RCU-protected pointer in a structure field.
948  */
949 #define RCU_POINTER_INITIALIZER(p, v) \
950 		.p = RCU_INITIALIZER(v)
951 
952 /*
953  * Does the specified offset indicate that the corresponding rcu_head
954  * structure can be handled by kvfree_rcu()?
955  */
956 #define __is_kvfree_rcu_offset(offset) ((offset) < 4096)
957 
958 /**
959  * kfree_rcu() - kfree an object after a grace period.
960  * @ptr: pointer to kfree for both single- and double-argument invocations.
961  * @rhf: the name of the struct rcu_head within the type of @ptr,
962  *       but only for double-argument invocations.
963  *
964  * Many rcu callbacks functions just call kfree() on the base structure.
965  * These functions are trivial, but their size adds up, and furthermore
966  * when they are used in a kernel module, that module must invoke the
967  * high-latency rcu_barrier() function at module-unload time.
968  *
969  * The kfree_rcu() function handles this issue.  Rather than encoding a
970  * function address in the embedded rcu_head structure, kfree_rcu() instead
971  * encodes the offset of the rcu_head structure within the base structure.
972  * Because the functions are not allowed in the low-order 4096 bytes of
973  * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
974  * If the offset is larger than 4095 bytes, a compile-time error will
975  * be generated in kvfree_rcu_arg_2(). If this error is triggered, you can
976  * either fall back to use of call_rcu() or rearrange the structure to
977  * position the rcu_head structure into the first 4096 bytes.
978  *
979  * Note that the allowable offset might decrease in the future, for example,
980  * to allow something like kmem_cache_free_rcu().
981  *
982  * The BUILD_BUG_ON check must not involve any function calls, hence the
983  * checks are done in macros here.
984  */
985 #define kfree_rcu(ptr, rhf...) kvfree_rcu(ptr, ## rhf)
986 
987 /**
988  * kvfree_rcu() - kvfree an object after a grace period.
989  *
990  * This macro consists of one or two arguments and it is
991  * based on whether an object is head-less or not. If it
992  * has a head then a semantic stays the same as it used
993  * to be before:
994  *
995  *     kvfree_rcu(ptr, rhf);
996  *
997  * where @ptr is a pointer to kvfree(), @rhf is the name
998  * of the rcu_head structure within the type of @ptr.
999  *
1000  * When it comes to head-less variant, only one argument
1001  * is passed and that is just a pointer which has to be
1002  * freed after a grace period. Therefore the semantic is
1003  *
1004  *     kvfree_rcu(ptr);
1005  *
1006  * where @ptr is the pointer to be freed by kvfree().
1007  *
1008  * Please note, head-less way of freeing is permitted to
1009  * use from a context that has to follow might_sleep()
1010  * annotation. Otherwise, please switch and embed the
1011  * rcu_head structure within the type of @ptr.
1012  */
1013 #define kvfree_rcu(...) KVFREE_GET_MACRO(__VA_ARGS__,		\
1014 	kvfree_rcu_arg_2, kvfree_rcu_arg_1)(__VA_ARGS__)
1015 
1016 #define kvfree_rcu_mightsleep(ptr) kvfree_rcu_arg_1(ptr)
1017 #define kfree_rcu_mightsleep(ptr) kvfree_rcu_mightsleep(ptr)
1018 
1019 #define KVFREE_GET_MACRO(_1, _2, NAME, ...) NAME
1020 #define kvfree_rcu_arg_2(ptr, rhf)					\
1021 do {									\
1022 	typeof (ptr) ___p = (ptr);					\
1023 									\
1024 	if (___p) {									\
1025 		BUILD_BUG_ON(!__is_kvfree_rcu_offset(offsetof(typeof(*(ptr)), rhf)));	\
1026 		kvfree_call_rcu(&((___p)->rhf), (void *) (___p));			\
1027 	}										\
1028 } while (0)
1029 
1030 #define kvfree_rcu_arg_1(ptr)					\
1031 do {								\
1032 	typeof(ptr) ___p = (ptr);				\
1033 								\
1034 	if (___p)						\
1035 		kvfree_call_rcu(NULL, (void *) (___p));		\
1036 } while (0)
1037 
1038 /*
1039  * Place this after a lock-acquisition primitive to guarantee that
1040  * an UNLOCK+LOCK pair acts as a full barrier.  This guarantee applies
1041  * if the UNLOCK and LOCK are executed by the same CPU or if the
1042  * UNLOCK and LOCK operate on the same lock variable.
1043  */
1044 #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE
1045 #define smp_mb__after_unlock_lock()	smp_mb()  /* Full ordering for lock. */
1046 #else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
1047 #define smp_mb__after_unlock_lock()	do { } while (0)
1048 #endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
1049 
1050 
1051 /* Has the specified rcu_head structure been handed to call_rcu()? */
1052 
1053 /**
1054  * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu()
1055  * @rhp: The rcu_head structure to initialize.
1056  *
1057  * If you intend to invoke rcu_head_after_call_rcu() to test whether a
1058  * given rcu_head structure has already been passed to call_rcu(), then
1059  * you must also invoke this rcu_head_init() function on it just after
1060  * allocating that structure.  Calls to this function must not race with
1061  * calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation.
1062  */
rcu_head_init(struct rcu_head * rhp)1063 static inline void rcu_head_init(struct rcu_head *rhp)
1064 {
1065 	rhp->func = (rcu_callback_t)~0L;
1066 }
1067 
1068 /**
1069  * rcu_head_after_call_rcu() - Has this rcu_head been passed to call_rcu()?
1070  * @rhp: The rcu_head structure to test.
1071  * @f: The function passed to call_rcu() along with @rhp.
1072  *
1073  * Returns @true if the @rhp has been passed to call_rcu() with @func,
1074  * and @false otherwise.  Emits a warning in any other case, including
1075  * the case where @rhp has already been invoked after a grace period.
1076  * Calls to this function must not race with callback invocation.  One way
1077  * to avoid such races is to enclose the call to rcu_head_after_call_rcu()
1078  * in an RCU read-side critical section that includes a read-side fetch
1079  * of the pointer to the structure containing @rhp.
1080  */
1081 static inline bool
rcu_head_after_call_rcu(struct rcu_head * rhp,rcu_callback_t f)1082 rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f)
1083 {
1084 	rcu_callback_t func = READ_ONCE(rhp->func);
1085 
1086 	if (func == f)
1087 		return true;
1088 	WARN_ON_ONCE(func != (rcu_callback_t)~0L);
1089 	return false;
1090 }
1091 
1092 /* kernel/ksysfs.c definitions */
1093 extern int rcu_expedited;
1094 extern int rcu_normal;
1095 
1096 #endif /* __LINUX_RCUPDATE_H */
1097