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
24struct srcu_struct;
25
26#ifdef CONFIG_DEBUG_LOCK_ALLOC
27
28int __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
41int 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. */
54struct srcu_struct { };
55#endif
56
57void call_srcu(struct srcu_struct *ssp, struct rcu_head *head,
58 void (*func)(struct rcu_head *head));
59void _cleanup_srcu_struct(struct srcu_struct *ssp, bool quiesced);
60int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp);
61void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases(ssp);
62void synchronize_srcu(struct srcu_struct *ssp);
63
64/**
65 * cleanup_srcu_struct - deconstruct a sleep-RCU structure
66 * @ssp: structure to clean up.
67 *
68 * Must invoke this after you are finished using a given srcu_struct that
69 * was initialized via init_srcu_struct(), else you leak memory.
70 */
71static inline void cleanup_srcu_struct(struct srcu_struct *ssp)
72{
73 _cleanup_srcu_struct(ssp, false);
74}
75
76/**
77 * cleanup_srcu_struct_quiesced - deconstruct a quiesced sleep-RCU structure
78 * @ssp: structure to clean up.
79 *
80 * Must invoke this after you are finished using a given srcu_struct that
81 * was initialized via init_srcu_struct(), else you leak memory. Also,
82 * all grace-period processing must have completed.
83 *
84 * "Completed" means that the last synchronize_srcu() and
85 * synchronize_srcu_expedited() calls must have returned before the call
86 * to cleanup_srcu_struct_quiesced(). It also means that the callback
87 * from the last call_srcu() must have been invoked before the call to
88 * cleanup_srcu_struct_quiesced(), but you can use srcu_barrier() to help
89 * with this last. Violating these rules will get you a WARN_ON() splat
90 * (with high probability, anyway), and will also cause the srcu_struct
91 * to be leaked.
92 */
93static inline void cleanup_srcu_struct_quiesced(struct srcu_struct *ssp)
94{
95 _cleanup_srcu_struct(ssp, true);
96}
97
98#ifdef CONFIG_DEBUG_LOCK_ALLOC
99
100/**
101 * srcu_read_lock_held - might we be in SRCU read-side critical section?
102 * @ssp: The srcu_struct structure to check
103 *
104 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
105 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
106 * this assumes we are in an SRCU read-side critical section unless it can
107 * prove otherwise.
108 *
109 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
110 * and while lockdep is disabled.
111 *
112 * Note that SRCU is based on its own statemachine and it doesn't
113 * relies on normal RCU, it can be called from the CPU which
114 * is in the idle loop from an RCU point of view or offline.
115 */
116static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
117{
118 if (!debug_lockdep_rcu_enabled())
119 return 1;
120 return lock_is_held(&ssp->dep_map);
121}
122
123#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
124
125static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
126{
127 return 1;
128}
129
130#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
131
132/**
133 * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
134 * @p: the pointer to fetch and protect for later dereferencing
135 * @ssp: pointer to the srcu_struct, which is used to check that we
136 * really are in an SRCU read-side critical section.
137 * @c: condition to check for update-side use
138 *
139 * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
140 * critical section will result in an RCU-lockdep splat, unless @c evaluates
141 * to 1. The @c argument will normally be a logical expression containing
142 * lockdep_is_held() calls.
143 */
144#define srcu_dereference_check(p, ssp, c) \
145 __rcu_dereference_check((p), (c) || srcu_read_lock_held(ssp), __rcu)
146
147/**
148 * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
149 * @p: the pointer to fetch and protect for later dereferencing
150 * @ssp: pointer to the srcu_struct, which is used to check that we
151 * really are in an SRCU read-side critical section.
152 *
153 * Makes rcu_dereference_check() do the dirty work. If PROVE_RCU
154 * is enabled, invoking this outside of an RCU read-side critical
155 * section will result in an RCU-lockdep splat.
156 */
157#define srcu_dereference(p, ssp) srcu_dereference_check((p), (ssp), 0)
158
159/**
160 * srcu_dereference_notrace - no tracing and no lockdep calls from here
161 * @p: the pointer to fetch and protect for later dereferencing
162 * @ssp: pointer to the srcu_struct, which is used to check that we
163 * really are in an SRCU read-side critical section.
164 */
165#define srcu_dereference_notrace(p, ssp) srcu_dereference_check((p), (ssp), 1)
166
167/**
168 * srcu_read_lock - register a new reader for an SRCU-protected structure.
169 * @ssp: srcu_struct in which to register the new reader.
170 *
171 * Enter an SRCU read-side critical section. Note that SRCU read-side
172 * critical sections may be nested. However, it is illegal to
173 * call anything that waits on an SRCU grace period for the same
174 * srcu_struct, whether directly or indirectly. Please note that
175 * one way to indirectly wait on an SRCU grace period is to acquire
176 * a mutex that is held elsewhere while calling synchronize_srcu() or
177 * synchronize_srcu_expedited().
178 *
179 * Note that srcu_read_lock() and the matching srcu_read_unlock() must
180 * occur in the same context, for example, it is illegal to invoke
181 * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
182 * was invoked in process context.
183 */
184static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
185{
186 int retval;
187
188 retval = __srcu_read_lock(ssp);
189 rcu_lock_acquire(&(ssp)->dep_map);
190 return retval;
191}
192
193/* Used by tracing, cannot be traced and cannot invoke lockdep. */
194static inline notrace int
195srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
196{
197 int retval;
198
199 retval = __srcu_read_lock(ssp);
200 return retval;
201}
202
203/**
204 * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
205 * @ssp: srcu_struct in which to unregister the old reader.
206 * @idx: return value from corresponding srcu_read_lock().
207 *
208 * Exit an SRCU read-side critical section.
209 */
210static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx)
211 __releases(ssp)
212{
213 WARN_ON_ONCE(idx & ~0x1);
214 rcu_lock_release(&(ssp)->dep_map);
215 __srcu_read_unlock(ssp, idx);
216}
217
218/* Used by tracing, cannot be traced and cannot call lockdep. */
219static inline notrace void
220srcu_read_unlock_notrace(struct srcu_struct *ssp, int idx) __releases(ssp)
221{
222 __srcu_read_unlock(ssp, idx);
223}
224
225/**
226 * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
227 *
228 * Converts the preceding srcu_read_unlock into a two-way memory barrier.
229 *
230 * Call this after srcu_read_unlock, to guarantee that all memory operations
231 * that occur after smp_mb__after_srcu_read_unlock will appear to happen after
232 * the preceding srcu_read_unlock.
233 */
234static inline void smp_mb__after_srcu_read_unlock(void)
235{
236 /* __srcu_read_unlock has smp_mb() internally so nothing to do here. */
237}
238
239#endif
240