1 /*
2 * Sleepable Read-Copy Update mechanism for mutual exclusion
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, you can access it online at
16 * http://www.gnu.org/licenses/gpl-2.0.html.
17 *
18 * Copyright (C) IBM Corporation, 2006
19 * Copyright (C) Fujitsu, 2012
20 *
21 * Author: Paul McKenney <paulmck@us.ibm.com>
22 * Lai Jiangshan <laijs@cn.fujitsu.com>
23 *
24 * For detailed explanation of Read-Copy Update mechanism see -
25 * Documentation/RCU/ *.txt
26 *
27 */
28
29 #ifndef _LINUX_SRCU_H
30 #define _LINUX_SRCU_H
31
32 #include <linux/mutex.h>
33 #include <linux/rcupdate.h>
34 #include <linux/workqueue.h>
35
36 struct srcu_struct_array {
37 unsigned long c[2];
38 unsigned long seq[2];
39 };
40
41 struct rcu_batch {
42 struct rcu_head *head, **tail;
43 };
44
45 #define RCU_BATCH_INIT(name) { NULL, &(name.head) }
46
47 struct srcu_struct {
48 unsigned completed;
49 struct srcu_struct_array __percpu *per_cpu_ref;
50 spinlock_t queue_lock; /* protect ->batch_queue, ->running */
51 bool running;
52 /* callbacks just queued */
53 struct rcu_batch batch_queue;
54 /* callbacks try to do the first check_zero */
55 struct rcu_batch batch_check0;
56 /* callbacks done with the first check_zero and the flip */
57 struct rcu_batch batch_check1;
58 struct rcu_batch batch_done;
59 struct delayed_work work;
60 #ifdef CONFIG_DEBUG_LOCK_ALLOC
61 struct lockdep_map dep_map;
62 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
63 };
64
65 #ifdef CONFIG_DEBUG_LOCK_ALLOC
66
67 int __init_srcu_struct(struct srcu_struct *sp, const char *name,
68 struct lock_class_key *key);
69
70 #define init_srcu_struct(sp) \
71 ({ \
72 static struct lock_class_key __srcu_key; \
73 \
74 __init_srcu_struct((sp), #sp, &__srcu_key); \
75 })
76
77 #define __SRCU_DEP_MAP_INIT(srcu_name) .dep_map = { .name = #srcu_name },
78 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
79
80 int init_srcu_struct(struct srcu_struct *sp);
81
82 #define __SRCU_DEP_MAP_INIT(srcu_name)
83 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
84
85 void process_srcu(struct work_struct *work);
86
87 #define __SRCU_STRUCT_INIT(name) \
88 { \
89 .completed = -300, \
90 .per_cpu_ref = &name##_srcu_array, \
91 .queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock), \
92 .running = false, \
93 .batch_queue = RCU_BATCH_INIT(name.batch_queue), \
94 .batch_check0 = RCU_BATCH_INIT(name.batch_check0), \
95 .batch_check1 = RCU_BATCH_INIT(name.batch_check1), \
96 .batch_done = RCU_BATCH_INIT(name.batch_done), \
97 .work = __DELAYED_WORK_INITIALIZER(name.work, process_srcu, 0),\
98 __SRCU_DEP_MAP_INIT(name) \
99 }
100
101 /*
102 * define and init a srcu struct at build time.
103 * dont't call init_srcu_struct() nor cleanup_srcu_struct() on it.
104 */
105 #define DEFINE_SRCU(name) \
106 static DEFINE_PER_CPU(struct srcu_struct_array, name##_srcu_array);\
107 struct srcu_struct name = __SRCU_STRUCT_INIT(name);
108
109 #define DEFINE_STATIC_SRCU(name) \
110 static DEFINE_PER_CPU(struct srcu_struct_array, name##_srcu_array);\
111 static struct srcu_struct name = __SRCU_STRUCT_INIT(name);
112
113 /**
114 * call_srcu() - Queue a callback for invocation after an SRCU grace period
115 * @sp: srcu_struct in queue the callback
116 * @head: structure to be used for queueing the SRCU callback.
117 * @func: function to be invoked after the SRCU grace period
118 *
119 * The callback function will be invoked some time after a full SRCU
120 * grace period elapses, in other words after all pre-existing SRCU
121 * read-side critical sections have completed. However, the callback
122 * function might well execute concurrently with other SRCU read-side
123 * critical sections that started after call_srcu() was invoked. SRCU
124 * read-side critical sections are delimited by srcu_read_lock() and
125 * srcu_read_unlock(), and may be nested.
126 *
127 * The callback will be invoked from process context, but must nevertheless
128 * be fast and must not block.
129 */
130 void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
131 void (*func)(struct rcu_head *head));
132
133 void cleanup_srcu_struct(struct srcu_struct *sp);
134 int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
135 void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
136 void synchronize_srcu(struct srcu_struct *sp);
137 void synchronize_srcu_expedited(struct srcu_struct *sp);
138 long srcu_batches_completed(struct srcu_struct *sp);
139 void srcu_barrier(struct srcu_struct *sp);
140
141 #ifdef CONFIG_DEBUG_LOCK_ALLOC
142
143 /**
144 * srcu_read_lock_held - might we be in SRCU read-side critical section?
145 *
146 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
147 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
148 * this assumes we are in an SRCU read-side critical section unless it can
149 * prove otherwise.
150 *
151 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
152 * and while lockdep is disabled.
153 *
154 * Note that SRCU is based on its own statemachine and it doesn't
155 * relies on normal RCU, it can be called from the CPU which
156 * is in the idle loop from an RCU point of view or offline.
157 */
srcu_read_lock_held(struct srcu_struct * sp)158 static inline int srcu_read_lock_held(struct srcu_struct *sp)
159 {
160 if (!debug_lockdep_rcu_enabled())
161 return 1;
162 return lock_is_held(&sp->dep_map);
163 }
164
165 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
166
srcu_read_lock_held(struct srcu_struct * sp)167 static inline int srcu_read_lock_held(struct srcu_struct *sp)
168 {
169 return 1;
170 }
171
172 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
173
174 /**
175 * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
176 * @p: the pointer to fetch and protect for later dereferencing
177 * @sp: pointer to the srcu_struct, which is used to check that we
178 * really are in an SRCU read-side critical section.
179 * @c: condition to check for update-side use
180 *
181 * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
182 * critical section will result in an RCU-lockdep splat, unless @c evaluates
183 * to 1. The @c argument will normally be a logical expression containing
184 * lockdep_is_held() calls.
185 */
186 #define srcu_dereference_check(p, sp, c) \
187 __rcu_dereference_check((p), srcu_read_lock_held(sp) || (c), __rcu)
188
189 /**
190 * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
191 * @p: the pointer to fetch and protect for later dereferencing
192 * @sp: pointer to the srcu_struct, which is used to check that we
193 * really are in an SRCU read-side critical section.
194 *
195 * Makes rcu_dereference_check() do the dirty work. If PROVE_RCU
196 * is enabled, invoking this outside of an RCU read-side critical
197 * section will result in an RCU-lockdep splat.
198 */
199 #define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0)
200
201 /**
202 * srcu_read_lock - register a new reader for an SRCU-protected structure.
203 * @sp: srcu_struct in which to register the new reader.
204 *
205 * Enter an SRCU read-side critical section. Note that SRCU read-side
206 * critical sections may be nested. However, it is illegal to
207 * call anything that waits on an SRCU grace period for the same
208 * srcu_struct, whether directly or indirectly. Please note that
209 * one way to indirectly wait on an SRCU grace period is to acquire
210 * a mutex that is held elsewhere while calling synchronize_srcu() or
211 * synchronize_srcu_expedited().
212 *
213 * Note that srcu_read_lock() and the matching srcu_read_unlock() must
214 * occur in the same context, for example, it is illegal to invoke
215 * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
216 * was invoked in process context.
217 */
srcu_read_lock(struct srcu_struct * sp)218 static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
219 {
220 int retval = __srcu_read_lock(sp);
221
222 rcu_lock_acquire(&(sp)->dep_map);
223 return retval;
224 }
225
226 /**
227 * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
228 * @sp: srcu_struct in which to unregister the old reader.
229 * @idx: return value from corresponding srcu_read_lock().
230 *
231 * Exit an SRCU read-side critical section.
232 */
srcu_read_unlock(struct srcu_struct * sp,int idx)233 static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
234 __releases(sp)
235 {
236 rcu_lock_release(&(sp)->dep_map);
237 __srcu_read_unlock(sp, idx);
238 }
239
240 /**
241 * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
242 *
243 * Converts the preceding srcu_read_unlock into a two-way memory barrier.
244 *
245 * Call this after srcu_read_unlock, to guarantee that all memory operations
246 * that occur after smp_mb__after_srcu_read_unlock will appear to happen after
247 * the preceding srcu_read_unlock.
248 */
smp_mb__after_srcu_read_unlock(void)249 static inline void smp_mb__after_srcu_read_unlock(void)
250 {
251 /* __srcu_read_unlock has smp_mb() internally so nothing to do here. */
252 }
253
254 #endif
255