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 unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp);
61 unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp);
62 bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie);
63 
64 #ifdef CONFIG_NEED_SRCU_NMI_SAFE
65 int __srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp);
66 void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx) __releases(ssp);
67 #else
__srcu_read_lock_nmisafe(struct srcu_struct * ssp)68 static inline int __srcu_read_lock_nmisafe(struct srcu_struct *ssp)
69 {
70 	return __srcu_read_lock(ssp);
71 }
__srcu_read_unlock_nmisafe(struct srcu_struct * ssp,int idx)72 static inline void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
73 {
74 	__srcu_read_unlock(ssp, idx);
75 }
76 #endif /* CONFIG_NEED_SRCU_NMI_SAFE */
77 
78 void srcu_init(void);
79 
80 #ifdef CONFIG_DEBUG_LOCK_ALLOC
81 
82 /**
83  * srcu_read_lock_held - might we be in SRCU read-side critical section?
84  * @ssp: The srcu_struct structure to check
85  *
86  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
87  * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
88  * this assumes we are in an SRCU read-side critical section unless it can
89  * prove otherwise.
90  *
91  * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
92  * and while lockdep is disabled.
93  *
94  * Note that SRCU is based on its own statemachine and it doesn't
95  * relies on normal RCU, it can be called from the CPU which
96  * is in the idle loop from an RCU point of view or offline.
97  */
srcu_read_lock_held(const struct srcu_struct * ssp)98 static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
99 {
100 	if (!debug_lockdep_rcu_enabled())
101 		return 1;
102 	return lock_is_held(&ssp->dep_map);
103 }
104 
105 /*
106  * Annotations provide deadlock detection for SRCU.
107  *
108  * Similar to other lockdep annotations, except there is an additional
109  * srcu_lock_sync(), which is basically an empty *write*-side critical section,
110  * see lock_sync() for more information.
111  */
112 
113 /* Annotates a srcu_read_lock() */
srcu_lock_acquire(struct lockdep_map * map)114 static inline void srcu_lock_acquire(struct lockdep_map *map)
115 {
116 	lock_map_acquire_read(map);
117 }
118 
119 /* Annotates a srcu_read_lock() */
srcu_lock_release(struct lockdep_map * map)120 static inline void srcu_lock_release(struct lockdep_map *map)
121 {
122 	lock_map_release(map);
123 }
124 
125 /* Annotates a synchronize_srcu() */
srcu_lock_sync(struct lockdep_map * map)126 static inline void srcu_lock_sync(struct lockdep_map *map)
127 {
128 	lock_map_sync(map);
129 }
130 
131 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
132 
srcu_read_lock_held(const struct srcu_struct * ssp)133 static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
134 {
135 	return 1;
136 }
137 
138 #define srcu_lock_acquire(m) do { } while (0)
139 #define srcu_lock_release(m) do { } while (0)
140 #define srcu_lock_sync(m) do { } while (0)
141 
142 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
143 
144 #define SRCU_NMI_UNKNOWN	0x0
145 #define SRCU_NMI_UNSAFE		0x1
146 #define SRCU_NMI_SAFE		0x2
147 
148 #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_TREE_SRCU)
149 void srcu_check_nmi_safety(struct srcu_struct *ssp, bool nmi_safe);
150 #else
srcu_check_nmi_safety(struct srcu_struct * ssp,bool nmi_safe)151 static inline void srcu_check_nmi_safety(struct srcu_struct *ssp,
152 					 bool nmi_safe) { }
153 #endif
154 
155 
156 /**
157  * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
158  * @p: the pointer to fetch and protect for later dereferencing
159  * @ssp: pointer to the srcu_struct, which is used to check that we
160  *	really are in an SRCU read-side critical section.
161  * @c: condition to check for update-side use
162  *
163  * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
164  * critical section will result in an RCU-lockdep splat, unless @c evaluates
165  * to 1.  The @c argument will normally be a logical expression containing
166  * lockdep_is_held() calls.
167  */
168 #define srcu_dereference_check(p, ssp, c) \
169 	__rcu_dereference_check((p), __UNIQUE_ID(rcu), \
170 				(c) || srcu_read_lock_held(ssp), __rcu)
171 
172 /**
173  * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
174  * @p: the pointer to fetch and protect for later dereferencing
175  * @ssp: pointer to the srcu_struct, which is used to check that we
176  *	really are in an SRCU read-side critical section.
177  *
178  * Makes rcu_dereference_check() do the dirty work.  If PROVE_RCU
179  * is enabled, invoking this outside of an RCU read-side critical
180  * section will result in an RCU-lockdep splat.
181  */
182 #define srcu_dereference(p, ssp) srcu_dereference_check((p), (ssp), 0)
183 
184 /**
185  * srcu_dereference_notrace - no tracing and no lockdep calls from here
186  * @p: the pointer to fetch and protect for later dereferencing
187  * @ssp: pointer to the srcu_struct, which is used to check that we
188  *	really are in an SRCU read-side critical section.
189  */
190 #define srcu_dereference_notrace(p, ssp) srcu_dereference_check((p), (ssp), 1)
191 
192 /**
193  * srcu_read_lock - register a new reader for an SRCU-protected structure.
194  * @ssp: srcu_struct in which to register the new reader.
195  *
196  * Enter an SRCU read-side critical section.  Note that SRCU read-side
197  * critical sections may be nested.  However, it is illegal to
198  * call anything that waits on an SRCU grace period for the same
199  * srcu_struct, whether directly or indirectly.  Please note that
200  * one way to indirectly wait on an SRCU grace period is to acquire
201  * a mutex that is held elsewhere while calling synchronize_srcu() or
202  * synchronize_srcu_expedited().
203  *
204  * Note that srcu_read_lock() and the matching srcu_read_unlock() must
205  * occur in the same context, for example, it is illegal to invoke
206  * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
207  * was invoked in process context.
208  */
srcu_read_lock(struct srcu_struct * ssp)209 static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
210 {
211 	int retval;
212 
213 	srcu_check_nmi_safety(ssp, false);
214 	retval = __srcu_read_lock(ssp);
215 	srcu_lock_acquire(&ssp->dep_map);
216 	return retval;
217 }
218 
219 /**
220  * srcu_read_lock_nmisafe - register a new reader for an SRCU-protected structure.
221  * @ssp: srcu_struct in which to register the new reader.
222  *
223  * Enter an SRCU read-side critical section, but in an NMI-safe manner.
224  * See srcu_read_lock() for more information.
225  */
srcu_read_lock_nmisafe(struct srcu_struct * ssp)226 static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp)
227 {
228 	int retval;
229 
230 	srcu_check_nmi_safety(ssp, true);
231 	retval = __srcu_read_lock_nmisafe(ssp);
232 	rcu_try_lock_acquire(&ssp->dep_map);
233 	return retval;
234 }
235 
236 /* Used by tracing, cannot be traced and cannot invoke lockdep. */
237 static inline notrace int
srcu_read_lock_notrace(struct srcu_struct * ssp)238 srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
239 {
240 	int retval;
241 
242 	srcu_check_nmi_safety(ssp, false);
243 	retval = __srcu_read_lock(ssp);
244 	return retval;
245 }
246 
247 /**
248  * srcu_down_read - register a new reader for an SRCU-protected structure.
249  * @ssp: srcu_struct in which to register the new reader.
250  *
251  * Enter a semaphore-like SRCU read-side critical section.  Note that
252  * SRCU read-side critical sections may be nested.  However, it is
253  * illegal to call anything that waits on an SRCU grace period for the
254  * same srcu_struct, whether directly or indirectly.  Please note that
255  * one way to indirectly wait on an SRCU grace period is to acquire
256  * a mutex that is held elsewhere while calling synchronize_srcu() or
257  * synchronize_srcu_expedited().  But if you want lockdep to help you
258  * keep this stuff straight, you should instead use srcu_read_lock().
259  *
260  * The semaphore-like nature of srcu_down_read() means that the matching
261  * srcu_up_read() can be invoked from some other context, for example,
262  * from some other task or from an irq handler.  However, neither
263  * srcu_down_read() nor srcu_up_read() may be invoked from an NMI handler.
264  *
265  * Calls to srcu_down_read() may be nested, similar to the manner in
266  * which calls to down_read() may be nested.
267  */
srcu_down_read(struct srcu_struct * ssp)268 static inline int srcu_down_read(struct srcu_struct *ssp) __acquires(ssp)
269 {
270 	WARN_ON_ONCE(in_nmi());
271 	srcu_check_nmi_safety(ssp, false);
272 	return __srcu_read_lock(ssp);
273 }
274 
275 /**
276  * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
277  * @ssp: srcu_struct in which to unregister the old reader.
278  * @idx: return value from corresponding srcu_read_lock().
279  *
280  * Exit an SRCU read-side critical section.
281  */
srcu_read_unlock(struct srcu_struct * ssp,int idx)282 static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx)
283 	__releases(ssp)
284 {
285 	WARN_ON_ONCE(idx & ~0x1);
286 	srcu_check_nmi_safety(ssp, false);
287 	srcu_lock_release(&ssp->dep_map);
288 	__srcu_read_unlock(ssp, idx);
289 }
290 
291 /**
292  * srcu_read_unlock_nmisafe - unregister a old reader from an SRCU-protected structure.
293  * @ssp: srcu_struct in which to unregister the old reader.
294  * @idx: return value from corresponding srcu_read_lock().
295  *
296  * Exit an SRCU read-side critical section, but in an NMI-safe manner.
297  */
srcu_read_unlock_nmisafe(struct srcu_struct * ssp,int idx)298 static inline void srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
299 	__releases(ssp)
300 {
301 	WARN_ON_ONCE(idx & ~0x1);
302 	srcu_check_nmi_safety(ssp, true);
303 	rcu_lock_release(&ssp->dep_map);
304 	__srcu_read_unlock_nmisafe(ssp, idx);
305 }
306 
307 /* Used by tracing, cannot be traced and cannot call lockdep. */
308 static inline notrace void
srcu_read_unlock_notrace(struct srcu_struct * ssp,int idx)309 srcu_read_unlock_notrace(struct srcu_struct *ssp, int idx) __releases(ssp)
310 {
311 	srcu_check_nmi_safety(ssp, false);
312 	__srcu_read_unlock(ssp, idx);
313 }
314 
315 /**
316  * srcu_up_read - unregister a old reader from an SRCU-protected structure.
317  * @ssp: srcu_struct in which to unregister the old reader.
318  * @idx: return value from corresponding srcu_read_lock().
319  *
320  * Exit an SRCU read-side critical section, but not necessarily from
321  * the same context as the maching srcu_down_read().
322  */
srcu_up_read(struct srcu_struct * ssp,int idx)323 static inline void srcu_up_read(struct srcu_struct *ssp, int idx)
324 	__releases(ssp)
325 {
326 	WARN_ON_ONCE(idx & ~0x1);
327 	WARN_ON_ONCE(in_nmi());
328 	srcu_check_nmi_safety(ssp, false);
329 	__srcu_read_unlock(ssp, idx);
330 }
331 
332 /**
333  * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
334  *
335  * Converts the preceding srcu_read_unlock into a two-way memory barrier.
336  *
337  * Call this after srcu_read_unlock, to guarantee that all memory operations
338  * that occur after smp_mb__after_srcu_read_unlock will appear to happen after
339  * the preceding srcu_read_unlock.
340  */
smp_mb__after_srcu_read_unlock(void)341 static inline void smp_mb__after_srcu_read_unlock(void)
342 {
343 	/* __srcu_read_unlock has smp_mb() internally so nothing to do here. */
344 }
345 
346 DEFINE_LOCK_GUARD_1(srcu, struct srcu_struct,
347 		    _T->idx = srcu_read_lock(_T->lock),
348 		    srcu_read_unlock(_T->lock, _T->idx),
349 		    int idx)
350 
351 #endif
352