1 /* SPDX-License-Identifier: GPL-2.0+ */
2 /*
3 * Sleepable Read-Copy Update mechanism for mutual exclusion
4 *
5 * Copyright (C) IBM Corporation, 2006
6 * Copyright (C) Fujitsu, 2012
7 *
8 * Author: Paul McKenney <paulmck@linux.ibm.com>
9 * Lai Jiangshan <laijs@cn.fujitsu.com>
10 *
11 * For detailed explanation of Read-Copy Update mechanism see -
12 * Documentation/RCU/ *.txt
13 *
14 */
15
16 #ifndef _LINUX_SRCU_H
17 #define _LINUX_SRCU_H
18
19 #include <linux/mutex.h>
20 #include <linux/rcupdate.h>
21 #include <linux/workqueue.h>
22 #include <linux/rcu_segcblist.h>
23
24 struct srcu_struct;
25
26 #ifdef CONFIG_DEBUG_LOCK_ALLOC
27
28 int __init_srcu_struct(struct srcu_struct *ssp, const char *name,
29 struct lock_class_key *key);
30
31 #define init_srcu_struct(ssp) \
32 ({ \
33 static struct lock_class_key __srcu_key; \
34 \
35 __init_srcu_struct((ssp), #ssp, &__srcu_key); \
36 })
37
38 #define __SRCU_DEP_MAP_INIT(srcu_name) .dep_map = { .name = #srcu_name },
39 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
40
41 int init_srcu_struct(struct srcu_struct *ssp);
42
43 #define __SRCU_DEP_MAP_INIT(srcu_name)
44 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
45
46 #ifdef CONFIG_TINY_SRCU
47 #include <linux/srcutiny.h>
48 #elif defined(CONFIG_TREE_SRCU)
49 #include <linux/srcutree.h>
50 #else
51 #error "Unknown SRCU implementation specified to kernel configuration"
52 #endif
53
54 void call_srcu(struct srcu_struct *ssp, struct rcu_head *head,
55 void (*func)(struct rcu_head *head));
56 void cleanup_srcu_struct(struct srcu_struct *ssp);
57 int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp);
58 void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases(ssp);
59 void synchronize_srcu(struct srcu_struct *ssp);
60
61 #define SRCU_GET_STATE_COMPLETED 0x1
62
63 /**
64 * get_completed_synchronize_srcu - Return a pre-completed polled state cookie
65 *
66 * Returns a value that poll_state_synchronize_srcu() will always treat
67 * as a cookie whose grace period has already completed.
68 */
69 static inline unsigned long get_completed_synchronize_srcu(void)
70 {
71 return SRCU_GET_STATE_COMPLETED;
72 }
73
74 unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp);
75 unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp);
76 bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie);
77
78 // Maximum number of unsigned long values corresponding to
79 // not-yet-completed SRCU grace periods.
80 #define NUM_ACTIVE_SRCU_POLL_OLDSTATE 2
81
82 /**
83 * same_state_synchronize_srcu - Are two old-state values identical?
84 * @oldstate1: First old-state value.
85 * @oldstate2: Second old-state value.
86 *
87 * The two old-state values must have been obtained from either
88 * get_state_synchronize_srcu(), start_poll_synchronize_srcu(), or
89 * get_completed_synchronize_srcu(). Returns @true if the two values are
90 * identical and @false otherwise. This allows structures whose lifetimes
91 * are tracked by old-state values to push these values to a list header,
92 * allowing those structures to be slightly smaller.
93 */
94 static inline bool same_state_synchronize_srcu(unsigned long oldstate1, unsigned long oldstate2)
95 {
96 return oldstate1 == oldstate2;
97 }
98
99 #ifdef CONFIG_NEED_SRCU_NMI_SAFE
100 int __srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp);
101 void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx) __releases(ssp);
102 #else
103 static inline int __srcu_read_lock_nmisafe(struct srcu_struct *ssp)
104 {
105 return __srcu_read_lock(ssp);
106 }
107 static inline void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
108 {
109 __srcu_read_unlock(ssp, idx);
110 }
111 #endif /* CONFIG_NEED_SRCU_NMI_SAFE */
112
113 void srcu_init(void);
114
115 #ifdef CONFIG_DEBUG_LOCK_ALLOC
116
117 /**
118 * srcu_read_lock_held - might we be in SRCU read-side critical section?
119 * @ssp: The srcu_struct structure to check
120 *
121 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
122 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
123 * this assumes we are in an SRCU read-side critical section unless it can
124 * prove otherwise.
125 *
126 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
127 * and while lockdep is disabled.
128 *
129 * Note that SRCU is based on its own statemachine and it doesn't
130 * relies on normal RCU, it can be called from the CPU which
131 * is in the idle loop from an RCU point of view or offline.
132 */
133 static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
134 {
135 if (!debug_lockdep_rcu_enabled())
136 return 1;
137 return lock_is_held(&ssp->dep_map);
138 }
139
140 /*
141 * Annotations provide deadlock detection for SRCU.
142 *
143 * Similar to other lockdep annotations, except there is an additional
144 * srcu_lock_sync(), which is basically an empty *write*-side critical section,
145 * see lock_sync() for more information.
146 */
147
148 /* Annotates a srcu_read_lock() */
149 static inline void srcu_lock_acquire(struct lockdep_map *map)
150 {
151 lock_map_acquire_read(map);
152 }
153
154 /* Annotates a srcu_read_lock() */
155 static inline void srcu_lock_release(struct lockdep_map *map)
156 {
157 lock_map_release(map);
158 }
159
160 /* Annotates a synchronize_srcu() */
161 static inline void srcu_lock_sync(struct lockdep_map *map)
162 {
163 lock_map_sync(map);
164 }
165
166 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
167
168 static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
169 {
170 return 1;
171 }
172
173 #define srcu_lock_acquire(m) do { } while (0)
174 #define srcu_lock_release(m) do { } while (0)
175 #define srcu_lock_sync(m) do { } while (0)
176
177 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
178
179 #define SRCU_NMI_UNKNOWN 0x0
180 #define SRCU_NMI_UNSAFE 0x1
181 #define SRCU_NMI_SAFE 0x2
182
183 #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_TREE_SRCU)
184 void srcu_check_nmi_safety(struct srcu_struct *ssp, bool nmi_safe);
185 #else
186 static inline void srcu_check_nmi_safety(struct srcu_struct *ssp,
187 bool nmi_safe) { }
188 #endif
189
190
191 /**
192 * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
193 * @p: the pointer to fetch and protect for later dereferencing
194 * @ssp: pointer to the srcu_struct, which is used to check that we
195 * really are in an SRCU read-side critical section.
196 * @c: condition to check for update-side use
197 *
198 * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
199 * critical section will result in an RCU-lockdep splat, unless @c evaluates
200 * to 1. The @c argument will normally be a logical expression containing
201 * lockdep_is_held() calls.
202 */
203 #define srcu_dereference_check(p, ssp, c) \
204 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
205 (c) || srcu_read_lock_held(ssp), __rcu)
206
207 /**
208 * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
209 * @p: the pointer to fetch and protect for later dereferencing
210 * @ssp: pointer to the srcu_struct, which is used to check that we
211 * really are in an SRCU read-side critical section.
212 *
213 * Makes rcu_dereference_check() do the dirty work. If PROVE_RCU
214 * is enabled, invoking this outside of an RCU read-side critical
215 * section will result in an RCU-lockdep splat.
216 */
217 #define srcu_dereference(p, ssp) srcu_dereference_check((p), (ssp), 0)
218
219 /**
220 * srcu_dereference_notrace - no tracing and no lockdep calls from here
221 * @p: the pointer to fetch and protect for later dereferencing
222 * @ssp: pointer to the srcu_struct, which is used to check that we
223 * really are in an SRCU read-side critical section.
224 */
225 #define srcu_dereference_notrace(p, ssp) srcu_dereference_check((p), (ssp), 1)
226
227 /**
228 * srcu_read_lock - register a new reader for an SRCU-protected structure.
229 * @ssp: srcu_struct in which to register the new reader.
230 *
231 * Enter an SRCU read-side critical section. Note that SRCU read-side
232 * critical sections may be nested. However, it is illegal to
233 * call anything that waits on an SRCU grace period for the same
234 * srcu_struct, whether directly or indirectly. Please note that
235 * one way to indirectly wait on an SRCU grace period is to acquire
236 * a mutex that is held elsewhere while calling synchronize_srcu() or
237 * synchronize_srcu_expedited().
238 *
239 * Note that srcu_read_lock() and the matching srcu_read_unlock() must
240 * occur in the same context, for example, it is illegal to invoke
241 * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
242 * was invoked in process context.
243 */
244 static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
245 {
246 int retval;
247
248 srcu_check_nmi_safety(ssp, false);
249 retval = __srcu_read_lock(ssp);
250 srcu_lock_acquire(&ssp->dep_map);
251 return retval;
252 }
253
254 /**
255 * srcu_read_lock_nmisafe - register a new reader for an SRCU-protected structure.
256 * @ssp: srcu_struct in which to register the new reader.
257 *
258 * Enter an SRCU read-side critical section, but in an NMI-safe manner.
259 * See srcu_read_lock() for more information.
260 */
261 static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp)
262 {
263 int retval;
264
265 srcu_check_nmi_safety(ssp, true);
266 retval = __srcu_read_lock_nmisafe(ssp);
267 rcu_try_lock_acquire(&ssp->dep_map);
268 return retval;
269 }
270
271 /* Used by tracing, cannot be traced and cannot invoke lockdep. */
272 static inline notrace int
273 srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
274 {
275 int retval;
276
277 srcu_check_nmi_safety(ssp, false);
278 retval = __srcu_read_lock(ssp);
279 return retval;
280 }
281
282 /**
283 * srcu_down_read - register a new reader for an SRCU-protected structure.
284 * @ssp: srcu_struct in which to register the new reader.
285 *
286 * Enter a semaphore-like SRCU read-side critical section. Note that
287 * SRCU read-side critical sections may be nested. However, it is
288 * illegal to call anything that waits on an SRCU grace period for the
289 * same srcu_struct, whether directly or indirectly. Please note that
290 * one way to indirectly wait on an SRCU grace period is to acquire
291 * a mutex that is held elsewhere while calling synchronize_srcu() or
292 * synchronize_srcu_expedited(). But if you want lockdep to help you
293 * keep this stuff straight, you should instead use srcu_read_lock().
294 *
295 * The semaphore-like nature of srcu_down_read() means that the matching
296 * srcu_up_read() can be invoked from some other context, for example,
297 * from some other task or from an irq handler. However, neither
298 * srcu_down_read() nor srcu_up_read() may be invoked from an NMI handler.
299 *
300 * Calls to srcu_down_read() may be nested, similar to the manner in
301 * which calls to down_read() may be nested.
302 */
303 static inline int srcu_down_read(struct srcu_struct *ssp) __acquires(ssp)
304 {
305 WARN_ON_ONCE(in_nmi());
306 srcu_check_nmi_safety(ssp, false);
307 return __srcu_read_lock(ssp);
308 }
309
310 /**
311 * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
312 * @ssp: srcu_struct in which to unregister the old reader.
313 * @idx: return value from corresponding srcu_read_lock().
314 *
315 * Exit an SRCU read-side critical section.
316 */
317 static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx)
318 __releases(ssp)
319 {
320 WARN_ON_ONCE(idx & ~0x1);
321 srcu_check_nmi_safety(ssp, false);
322 srcu_lock_release(&ssp->dep_map);
323 __srcu_read_unlock(ssp, idx);
324 }
325
326 /**
327 * srcu_read_unlock_nmisafe - unregister a old reader from an SRCU-protected structure.
328 * @ssp: srcu_struct in which to unregister the old reader.
329 * @idx: return value from corresponding srcu_read_lock().
330 *
331 * Exit an SRCU read-side critical section, but in an NMI-safe manner.
332 */
333 static inline void srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
334 __releases(ssp)
335 {
336 WARN_ON_ONCE(idx & ~0x1);
337 srcu_check_nmi_safety(ssp, true);
338 rcu_lock_release(&ssp->dep_map);
339 __srcu_read_unlock_nmisafe(ssp, idx);
340 }
341
342 /* Used by tracing, cannot be traced and cannot call lockdep. */
343 static inline notrace void
344 srcu_read_unlock_notrace(struct srcu_struct *ssp, int idx) __releases(ssp)
345 {
346 srcu_check_nmi_safety(ssp, false);
347 __srcu_read_unlock(ssp, idx);
348 }
349
350 /**
351 * srcu_up_read - unregister a old reader from an SRCU-protected structure.
352 * @ssp: srcu_struct in which to unregister the old reader.
353 * @idx: return value from corresponding srcu_read_lock().
354 *
355 * Exit an SRCU read-side critical section, but not necessarily from
356 * the same context as the maching srcu_down_read().
357 */
358 static inline void srcu_up_read(struct srcu_struct *ssp, int idx)
359 __releases(ssp)
360 {
361 WARN_ON_ONCE(idx & ~0x1);
362 WARN_ON_ONCE(in_nmi());
363 srcu_check_nmi_safety(ssp, false);
364 __srcu_read_unlock(ssp, idx);
365 }
366
367 /**
368 * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
369 *
370 * Converts the preceding srcu_read_unlock into a two-way memory barrier.
371 *
372 * Call this after srcu_read_unlock, to guarantee that all memory operations
373 * that occur after smp_mb__after_srcu_read_unlock will appear to happen after
374 * the preceding srcu_read_unlock.
375 */
376 static inline void smp_mb__after_srcu_read_unlock(void)
377 {
378 /* __srcu_read_unlock has smp_mb() internally so nothing to do here. */
379 }
380
381 /**
382 * smp_mb__after_srcu_read_lock - ensure full ordering after srcu_read_lock
383 *
384 * Converts the preceding srcu_read_lock into a two-way memory barrier.
385 *
386 * Call this after srcu_read_lock, to guarantee that all memory operations
387 * that occur after smp_mb__after_srcu_read_lock will appear to happen after
388 * the preceding srcu_read_lock.
389 */
390 static inline void smp_mb__after_srcu_read_lock(void)
391 {
392 /* __srcu_read_lock has smp_mb() internally so nothing to do here. */
393 }
394
395 DEFINE_LOCK_GUARD_1(srcu, struct srcu_struct,
396 _T->idx = srcu_read_lock(_T->lock),
397 srcu_read_unlock(_T->lock, _T->idx),
398 int idx)
399
400 #endif
401
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