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 long 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 initialize a srcu struct at build time.
103 * Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it.
104 *
105 * Note that although DEFINE_STATIC_SRCU() hides the name from other
106 * files, the per-CPU variable rules nevertheless require that the
107 * chosen name be globally unique. These rules also prohibit use of
108 * DEFINE_STATIC_SRCU() within a function. If these rules are too
109 * restrictive, declare the srcu_struct manually. For example, in
110 * each file:
111 *
112 * static struct srcu_struct my_srcu;
113 *
114 * Then, before the first use of each my_srcu, manually initialize it:
115 *
116 * init_srcu_struct(&my_srcu);
117 *
118 * See include/linux/percpu-defs.h for the rules on per-CPU variables.
119 */
120 #define __DEFINE_SRCU(name, is_static) \
121 static DEFINE_PER_CPU(struct srcu_struct_array, name##_srcu_array);\
122 is_static struct srcu_struct name = __SRCU_STRUCT_INIT(name)
123 #define DEFINE_SRCU(name) __DEFINE_SRCU(name, /* not static */)
124 #define DEFINE_STATIC_SRCU(name) __DEFINE_SRCU(name, static)
125
126 /**
127 * call_srcu() - Queue a callback for invocation after an SRCU grace period
128 * @sp: srcu_struct in queue the callback
129 * @head: structure to be used for queueing the SRCU callback.
130 * @func: function to be invoked after the SRCU grace period
131 *
132 * The callback function will be invoked some time after a full SRCU
133 * grace period elapses, in other words after all pre-existing SRCU
134 * read-side critical sections have completed. However, the callback
135 * function might well execute concurrently with other SRCU read-side
136 * critical sections that started after call_srcu() was invoked. SRCU
137 * read-side critical sections are delimited by srcu_read_lock() and
138 * srcu_read_unlock(), and may be nested.
139 *
140 * The callback will be invoked from process context, but must nevertheless
141 * be fast and must not block.
142 */
143 void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
144 void (*func)(struct rcu_head *head));
145
146 void cleanup_srcu_struct(struct srcu_struct *sp);
147 int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
148 void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
149 void synchronize_srcu(struct srcu_struct *sp);
150 void synchronize_srcu_expedited(struct srcu_struct *sp);
151 unsigned long srcu_batches_completed(struct srcu_struct *sp);
152 void srcu_barrier(struct srcu_struct *sp);
153
154 #ifdef CONFIG_DEBUG_LOCK_ALLOC
155
156 /**
157 * srcu_read_lock_held - might we be in SRCU read-side critical section?
158 *
159 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
160 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
161 * this assumes we are in an SRCU read-side critical section unless it can
162 * prove otherwise.
163 *
164 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
165 * and while lockdep is disabled.
166 *
167 * Note that SRCU is based on its own statemachine and it doesn't
168 * relies on normal RCU, it can be called from the CPU which
169 * is in the idle loop from an RCU point of view or offline.
170 */
srcu_read_lock_held(struct srcu_struct * sp)171 static inline int srcu_read_lock_held(struct srcu_struct *sp)
172 {
173 if (!debug_lockdep_rcu_enabled())
174 return 1;
175 return lock_is_held(&sp->dep_map);
176 }
177
178 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
179
srcu_read_lock_held(struct srcu_struct * sp)180 static inline int srcu_read_lock_held(struct srcu_struct *sp)
181 {
182 return 1;
183 }
184
185 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
186
187 /**
188 * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
189 * @p: the pointer to fetch and protect for later dereferencing
190 * @sp: pointer to the srcu_struct, which is used to check that we
191 * really are in an SRCU read-side critical section.
192 * @c: condition to check for update-side use
193 *
194 * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
195 * critical section will result in an RCU-lockdep splat, unless @c evaluates
196 * to 1. The @c argument will normally be a logical expression containing
197 * lockdep_is_held() calls.
198 */
199 #define srcu_dereference_check(p, sp, c) \
200 __rcu_dereference_check((p), (c) || srcu_read_lock_held(sp), __rcu)
201
202 /**
203 * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
204 * @p: the pointer to fetch and protect for later dereferencing
205 * @sp: pointer to the srcu_struct, which is used to check that we
206 * really are in an SRCU read-side critical section.
207 *
208 * Makes rcu_dereference_check() do the dirty work. If PROVE_RCU
209 * is enabled, invoking this outside of an RCU read-side critical
210 * section will result in an RCU-lockdep splat.
211 */
212 #define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0)
213
214 /**
215 * srcu_read_lock - register a new reader for an SRCU-protected structure.
216 * @sp: srcu_struct in which to register the new reader.
217 *
218 * Enter an SRCU read-side critical section. Note that SRCU read-side
219 * critical sections may be nested. However, it is illegal to
220 * call anything that waits on an SRCU grace period for the same
221 * srcu_struct, whether directly or indirectly. Please note that
222 * one way to indirectly wait on an SRCU grace period is to acquire
223 * a mutex that is held elsewhere while calling synchronize_srcu() or
224 * synchronize_srcu_expedited().
225 *
226 * Note that srcu_read_lock() and the matching srcu_read_unlock() must
227 * occur in the same context, for example, it is illegal to invoke
228 * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
229 * was invoked in process context.
230 */
srcu_read_lock(struct srcu_struct * sp)231 static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
232 {
233 int retval;
234
235 preempt_disable();
236 retval = __srcu_read_lock(sp);
237 preempt_enable();
238 rcu_lock_acquire(&(sp)->dep_map);
239 return retval;
240 }
241
242 /**
243 * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
244 * @sp: srcu_struct in which to unregister the old reader.
245 * @idx: return value from corresponding srcu_read_lock().
246 *
247 * Exit an SRCU read-side critical section.
248 */
srcu_read_unlock(struct srcu_struct * sp,int idx)249 static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
250 __releases(sp)
251 {
252 rcu_lock_release(&(sp)->dep_map);
253 __srcu_read_unlock(sp, idx);
254 }
255
256 /**
257 * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
258 *
259 * Converts the preceding srcu_read_unlock into a two-way memory barrier.
260 *
261 * Call this after srcu_read_unlock, to guarantee that all memory operations
262 * that occur after smp_mb__after_srcu_read_unlock will appear to happen after
263 * the preceding srcu_read_unlock.
264 */
smp_mb__after_srcu_read_unlock(void)265 static inline void smp_mb__after_srcu_read_unlock(void)
266 {
267 /* __srcu_read_unlock has smp_mb() internally so nothing to do here. */
268 }
269
270 #endif
271