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 #elif defined(CONFIG_SRCU)
51 #error "Unknown SRCU implementation specified to kernel configuration"
52 #else
53 /* Dummy definition for things like notifiers. Actual use gets link error. */
54 struct srcu_struct { };
55 #endif
56
57 void call_srcu(struct srcu_struct *ssp, struct rcu_head *head,
58 void (*func)(struct rcu_head *head));
59 void cleanup_srcu_struct(struct srcu_struct *ssp);
60 int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp);
61 void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases(ssp);
62 void synchronize_srcu(struct srcu_struct *ssp);
63
64 #ifdef CONFIG_DEBUG_LOCK_ALLOC
65
66 /**
67 * srcu_read_lock_held - might we be in SRCU read-side critical section?
68 * @ssp: The srcu_struct structure to check
69 *
70 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
71 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
72 * this assumes we are in an SRCU read-side critical section unless it can
73 * prove otherwise.
74 *
75 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
76 * and while lockdep is disabled.
77 *
78 * Note that SRCU is based on its own statemachine and it doesn't
79 * relies on normal RCU, it can be called from the CPU which
80 * is in the idle loop from an RCU point of view or offline.
81 */
82 static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
83 {
84 if (!debug_lockdep_rcu_enabled())
85 return 1;
86 return lock_is_held(&ssp->dep_map);
87 }
88
89 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
90
91 static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
92 {
93 return 1;
94 }
95
96 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
97
98 /**
99 * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
100 * @p: the pointer to fetch and protect for later dereferencing
101 * @ssp: pointer to the srcu_struct, which is used to check that we
102 * really are in an SRCU read-side critical section.
103 * @c: condition to check for update-side use
104 *
105 * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
106 * critical section will result in an RCU-lockdep splat, unless @c evaluates
107 * to 1. The @c argument will normally be a logical expression containing
108 * lockdep_is_held() calls.
109 */
110 #define srcu_dereference_check(p, ssp, c) \
111 __rcu_dereference_check((p), (c) || srcu_read_lock_held(ssp), __rcu)
112
113 /**
114 * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
115 * @p: the pointer to fetch and protect for later dereferencing
116 * @ssp: pointer to the srcu_struct, which is used to check that we
117 * really are in an SRCU read-side critical section.
118 *
119 * Makes rcu_dereference_check() do the dirty work. If PROVE_RCU
120 * is enabled, invoking this outside of an RCU read-side critical
121 * section will result in an RCU-lockdep splat.
122 */
123 #define srcu_dereference(p, ssp) srcu_dereference_check((p), (ssp), 0)
124
125 /**
126 * srcu_dereference_notrace - no tracing and no lockdep calls from here
127 * @p: the pointer to fetch and protect for later dereferencing
128 * @ssp: pointer to the srcu_struct, which is used to check that we
129 * really are in an SRCU read-side critical section.
130 */
131 #define srcu_dereference_notrace(p, ssp) srcu_dereference_check((p), (ssp), 1)
132
133 /**
134 * srcu_read_lock - register a new reader for an SRCU-protected structure.
135 * @ssp: srcu_struct in which to register the new reader.
136 *
137 * Enter an SRCU read-side critical section. Note that SRCU read-side
138 * critical sections may be nested. However, it is illegal to
139 * call anything that waits on an SRCU grace period for the same
140 * srcu_struct, whether directly or indirectly. Please note that
141 * one way to indirectly wait on an SRCU grace period is to acquire
142 * a mutex that is held elsewhere while calling synchronize_srcu() or
143 * synchronize_srcu_expedited().
144 *
145 * Note that srcu_read_lock() and the matching srcu_read_unlock() must
146 * occur in the same context, for example, it is illegal to invoke
147 * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
148 * was invoked in process context.
149 */
150 static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
151 {
152 int retval;
153
154 retval = __srcu_read_lock(ssp);
155 rcu_lock_acquire(&(ssp)->dep_map);
156 return retval;
157 }
158
159 /* Used by tracing, cannot be traced and cannot invoke lockdep. */
160 static inline notrace int
161 srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
162 {
163 int retval;
164
165 retval = __srcu_read_lock(ssp);
166 return retval;
167 }
168
169 /**
170 * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
171 * @ssp: srcu_struct in which to unregister the old reader.
172 * @idx: return value from corresponding srcu_read_lock().
173 *
174 * Exit an SRCU read-side critical section.
175 */
176 static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx)
177 __releases(ssp)
178 {
179 WARN_ON_ONCE(idx & ~0x1);
180 rcu_lock_release(&(ssp)->dep_map);
181 __srcu_read_unlock(ssp, idx);
182 }
183
184 /* Used by tracing, cannot be traced and cannot call lockdep. */
185 static inline notrace void
186 srcu_read_unlock_notrace(struct srcu_struct *ssp, int idx) __releases(ssp)
187 {
188 __srcu_read_unlock(ssp, idx);
189 }
190
191 /**
192 * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
193 *
194 * Converts the preceding srcu_read_unlock into a two-way memory barrier.
195 *
196 * Call this after srcu_read_unlock, to guarantee that all memory operations
197 * that occur after smp_mb__after_srcu_read_unlock will appear to happen after
198 * the preceding srcu_read_unlock.
199 */
200 static inline void smp_mb__after_srcu_read_unlock(void)
201 {
202 /* __srcu_read_unlock has smp_mb() internally so nothing to do here. */
203 }
204
205 #endif