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 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
106 
srcu_read_lock_held(const struct srcu_struct * ssp)107 static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
108 {
109 	return 1;
110 }
111 
112 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
113 
114 #define SRCU_NMI_UNKNOWN	0x0
115 #define SRCU_NMI_UNSAFE		0x1
116 #define SRCU_NMI_SAFE		0x2
117 
118 #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_TREE_SRCU)
119 void srcu_check_nmi_safety(struct srcu_struct *ssp, bool nmi_safe);
120 #else
srcu_check_nmi_safety(struct srcu_struct * ssp,bool nmi_safe)121 static inline void srcu_check_nmi_safety(struct srcu_struct *ssp,
122 					 bool nmi_safe) { }
123 #endif
124 
125 
126 /**
127  * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
128  * @p: the pointer to fetch and protect for later dereferencing
129  * @ssp: pointer to the srcu_struct, which is used to check that we
130  *	really are in an SRCU read-side critical section.
131  * @c: condition to check for update-side use
132  *
133  * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
134  * critical section will result in an RCU-lockdep splat, unless @c evaluates
135  * to 1.  The @c argument will normally be a logical expression containing
136  * lockdep_is_held() calls.
137  */
138 #define srcu_dereference_check(p, ssp, c) \
139 	__rcu_dereference_check((p), __UNIQUE_ID(rcu), \
140 				(c) || srcu_read_lock_held(ssp), __rcu)
141 
142 /**
143  * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
144  * @p: the pointer to fetch and protect for later dereferencing
145  * @ssp: pointer to the srcu_struct, which is used to check that we
146  *	really are in an SRCU read-side critical section.
147  *
148  * Makes rcu_dereference_check() do the dirty work.  If PROVE_RCU
149  * is enabled, invoking this outside of an RCU read-side critical
150  * section will result in an RCU-lockdep splat.
151  */
152 #define srcu_dereference(p, ssp) srcu_dereference_check((p), (ssp), 0)
153 
154 /**
155  * srcu_dereference_notrace - no tracing and no lockdep calls from here
156  * @p: the pointer to fetch and protect for later dereferencing
157  * @ssp: pointer to the srcu_struct, which is used to check that we
158  *	really are in an SRCU read-side critical section.
159  */
160 #define srcu_dereference_notrace(p, ssp) srcu_dereference_check((p), (ssp), 1)
161 
162 /**
163  * srcu_read_lock - register a new reader for an SRCU-protected structure.
164  * @ssp: srcu_struct in which to register the new reader.
165  *
166  * Enter an SRCU read-side critical section.  Note that SRCU read-side
167  * critical sections may be nested.  However, it is illegal to
168  * call anything that waits on an SRCU grace period for the same
169  * srcu_struct, whether directly or indirectly.  Please note that
170  * one way to indirectly wait on an SRCU grace period is to acquire
171  * a mutex that is held elsewhere while calling synchronize_srcu() or
172  * synchronize_srcu_expedited().
173  *
174  * Note that srcu_read_lock() and the matching srcu_read_unlock() must
175  * occur in the same context, for example, it is illegal to invoke
176  * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
177  * was invoked in process context.
178  */
srcu_read_lock(struct srcu_struct * ssp)179 static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
180 {
181 	int retval;
182 
183 	srcu_check_nmi_safety(ssp, false);
184 	retval = __srcu_read_lock(ssp);
185 	rcu_lock_acquire(&(ssp)->dep_map);
186 	return retval;
187 }
188 
189 /**
190  * srcu_read_lock_nmisafe - register a new reader for an SRCU-protected structure.
191  * @ssp: srcu_struct in which to register the new reader.
192  *
193  * Enter an SRCU read-side critical section, but in an NMI-safe manner.
194  * See srcu_read_lock() for more information.
195  */
srcu_read_lock_nmisafe(struct srcu_struct * ssp)196 static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp)
197 {
198 	int retval;
199 
200 	srcu_check_nmi_safety(ssp, true);
201 	retval = __srcu_read_lock_nmisafe(ssp);
202 	rcu_lock_acquire(&(ssp)->dep_map);
203 	return retval;
204 }
205 
206 /* Used by tracing, cannot be traced and cannot invoke lockdep. */
207 static inline notrace int
srcu_read_lock_notrace(struct srcu_struct * ssp)208 srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
209 {
210 	int retval;
211 
212 	srcu_check_nmi_safety(ssp, false);
213 	retval = __srcu_read_lock(ssp);
214 	return retval;
215 }
216 
217 /**
218  * srcu_down_read - register a new reader for an SRCU-protected structure.
219  * @ssp: srcu_struct in which to register the new reader.
220  *
221  * Enter a semaphore-like SRCU read-side critical section.  Note that
222  * SRCU read-side critical sections may be nested.  However, it is
223  * illegal to call anything that waits on an SRCU grace period for the
224  * same srcu_struct, whether directly or indirectly.  Please note that
225  * one way to indirectly wait on an SRCU grace period is to acquire
226  * a mutex that is held elsewhere while calling synchronize_srcu() or
227  * synchronize_srcu_expedited().  But if you want lockdep to help you
228  * keep this stuff straight, you should instead use srcu_read_lock().
229  *
230  * The semaphore-like nature of srcu_down_read() means that the matching
231  * srcu_up_read() can be invoked from some other context, for example,
232  * from some other task or from an irq handler.  However, neither
233  * srcu_down_read() nor srcu_up_read() may be invoked from an NMI handler.
234  *
235  * Calls to srcu_down_read() may be nested, similar to the manner in
236  * which calls to down_read() may be nested.
237  */
srcu_down_read(struct srcu_struct * ssp)238 static inline int srcu_down_read(struct srcu_struct *ssp) __acquires(ssp)
239 {
240 	WARN_ON_ONCE(in_nmi());
241 	srcu_check_nmi_safety(ssp, false);
242 	return __srcu_read_lock(ssp);
243 }
244 
245 /**
246  * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
247  * @ssp: srcu_struct in which to unregister the old reader.
248  * @idx: return value from corresponding srcu_read_lock().
249  *
250  * Exit an SRCU read-side critical section.
251  */
srcu_read_unlock(struct srcu_struct * ssp,int idx)252 static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx)
253 	__releases(ssp)
254 {
255 	WARN_ON_ONCE(idx & ~0x1);
256 	srcu_check_nmi_safety(ssp, false);
257 	rcu_lock_release(&(ssp)->dep_map);
258 	__srcu_read_unlock(ssp, idx);
259 }
260 
261 /**
262  * srcu_read_unlock_nmisafe - unregister a old reader from an SRCU-protected structure.
263  * @ssp: srcu_struct in which to unregister the old reader.
264  * @idx: return value from corresponding srcu_read_lock().
265  *
266  * Exit an SRCU read-side critical section, but in an NMI-safe manner.
267  */
srcu_read_unlock_nmisafe(struct srcu_struct * ssp,int idx)268 static inline void srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
269 	__releases(ssp)
270 {
271 	WARN_ON_ONCE(idx & ~0x1);
272 	srcu_check_nmi_safety(ssp, true);
273 	rcu_lock_release(&(ssp)->dep_map);
274 	__srcu_read_unlock_nmisafe(ssp, idx);
275 }
276 
277 /* Used by tracing, cannot be traced and cannot call lockdep. */
278 static inline notrace void
srcu_read_unlock_notrace(struct srcu_struct * ssp,int idx)279 srcu_read_unlock_notrace(struct srcu_struct *ssp, int idx) __releases(ssp)
280 {
281 	srcu_check_nmi_safety(ssp, false);
282 	__srcu_read_unlock(ssp, idx);
283 }
284 
285 /**
286  * srcu_up_read - unregister a old reader from an SRCU-protected structure.
287  * @ssp: srcu_struct in which to unregister the old reader.
288  * @idx: return value from corresponding srcu_read_lock().
289  *
290  * Exit an SRCU read-side critical section, but not necessarily from
291  * the same context as the maching srcu_down_read().
292  */
srcu_up_read(struct srcu_struct * ssp,int idx)293 static inline void srcu_up_read(struct srcu_struct *ssp, int idx)
294 	__releases(ssp)
295 {
296 	WARN_ON_ONCE(idx & ~0x1);
297 	WARN_ON_ONCE(in_nmi());
298 	srcu_check_nmi_safety(ssp, false);
299 	__srcu_read_unlock(ssp, idx);
300 }
301 
302 /**
303  * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
304  *
305  * Converts the preceding srcu_read_unlock into a two-way memory barrier.
306  *
307  * Call this after srcu_read_unlock, to guarantee that all memory operations
308  * that occur after smp_mb__after_srcu_read_unlock will appear to happen after
309  * the preceding srcu_read_unlock.
310  */
smp_mb__after_srcu_read_unlock(void)311 static inline void smp_mb__after_srcu_read_unlock(void)
312 {
313 	/* __srcu_read_unlock has smp_mb() internally so nothing to do here. */
314 }
315 
316 #endif
317