2 * Sleepable Read-Copy Update mechanism for mutual exclusion
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.
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.
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.
18 * Copyright (C) IBM Corporation, 2006
19 * Copyright (C) Fujitsu, 2012
21 * Author: Paul McKenney <paulmck@us.ibm.com>
22 * Lai Jiangshan <laijs@cn.fujitsu.com>
24 * For detailed explanation of Read-Copy Update mechanism see -
25 * Documentation/RCU/ *.txt
32 #include <linux/mutex.h>
33 #include <linux/rcupdate.h>
34 #include <linux/workqueue.h>
37 unsigned long lock_count[2];
38 unsigned long unlock_count[2];
42 struct rcu_head *head, **tail;
45 #define RCU_BATCH_INIT(name) { NULL, &(name.head) }
48 unsigned long completed;
49 unsigned long srcu_gp_seq;
50 struct srcu_array __percpu *per_cpu_ref;
51 spinlock_t queue_lock; /* protect ->batch_queue, ->running */
53 /* callbacks just queued */
54 struct rcu_batch batch_queue;
55 /* callbacks try to do the first check_zero */
56 struct rcu_batch batch_check0;
57 /* callbacks done with the first check_zero and the flip */
58 struct rcu_batch batch_check1;
59 struct rcu_batch batch_done;
60 struct delayed_work work;
61 #ifdef CONFIG_DEBUG_LOCK_ALLOC
62 struct lockdep_map dep_map;
63 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
66 /* Values for -> state variable. */
67 #define SRCU_STATE_IDLE 0
68 #define SRCU_STATE_SCAN1 1
69 #define SRCU_STATE_SCAN2 2
70 #define SRCU_STATE_DONE 3
72 #ifdef CONFIG_DEBUG_LOCK_ALLOC
74 int __init_srcu_struct(struct srcu_struct *sp, const char *name,
75 struct lock_class_key *key);
77 #define init_srcu_struct(sp) \
79 static struct lock_class_key __srcu_key; \
81 __init_srcu_struct((sp), #sp, &__srcu_key); \
84 #define __SRCU_DEP_MAP_INIT(srcu_name) .dep_map = { .name = #srcu_name },
85 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
87 int init_srcu_struct(struct srcu_struct *sp);
89 #define __SRCU_DEP_MAP_INIT(srcu_name)
90 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
92 void process_srcu(struct work_struct *work);
94 #define __SRCU_STRUCT_INIT(name) \
97 .per_cpu_ref = &name##_srcu_array, \
98 .queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock), \
99 .srcu_state = SRCU_STATE_IDLE, \
100 .batch_queue = RCU_BATCH_INIT(name.batch_queue), \
101 .batch_check0 = RCU_BATCH_INIT(name.batch_check0), \
102 .batch_check1 = RCU_BATCH_INIT(name.batch_check1), \
103 .batch_done = RCU_BATCH_INIT(name.batch_done), \
104 .work = __DELAYED_WORK_INITIALIZER(name.work, process_srcu, 0),\
105 __SRCU_DEP_MAP_INIT(name) \
109 * Define and initialize a srcu struct at build time.
110 * Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it.
112 * Note that although DEFINE_STATIC_SRCU() hides the name from other
113 * files, the per-CPU variable rules nevertheless require that the
114 * chosen name be globally unique. These rules also prohibit use of
115 * DEFINE_STATIC_SRCU() within a function. If these rules are too
116 * restrictive, declare the srcu_struct manually. For example, in
119 * static struct srcu_struct my_srcu;
121 * Then, before the first use of each my_srcu, manually initialize it:
123 * init_srcu_struct(&my_srcu);
125 * See include/linux/percpu-defs.h for the rules on per-CPU variables.
127 #define __DEFINE_SRCU(name, is_static) \
128 static DEFINE_PER_CPU(struct srcu_array, name##_srcu_array);\
129 is_static struct srcu_struct name = __SRCU_STRUCT_INIT(name)
130 #define DEFINE_SRCU(name) __DEFINE_SRCU(name, /* not static */)
131 #define DEFINE_STATIC_SRCU(name) __DEFINE_SRCU(name, static)
134 * call_srcu() - Queue a callback for invocation after an SRCU grace period
135 * @sp: srcu_struct in queue the callback
136 * @head: structure to be used for queueing the SRCU callback.
137 * @func: function to be invoked after the SRCU grace period
139 * The callback function will be invoked some time after a full SRCU
140 * grace period elapses, in other words after all pre-existing SRCU
141 * read-side critical sections have completed. However, the callback
142 * function might well execute concurrently with other SRCU read-side
143 * critical sections that started after call_srcu() was invoked. SRCU
144 * read-side critical sections are delimited by srcu_read_lock() and
145 * srcu_read_unlock(), and may be nested.
147 * The callback will be invoked from process context, but must nevertheless
148 * be fast and must not block.
150 void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
151 void (*func)(struct rcu_head *head));
153 void cleanup_srcu_struct(struct srcu_struct *sp);
154 int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
155 void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
156 void synchronize_srcu(struct srcu_struct *sp);
157 void synchronize_srcu_expedited(struct srcu_struct *sp);
158 unsigned long srcu_batches_completed(struct srcu_struct *sp);
159 void srcu_barrier(struct srcu_struct *sp);
161 #ifdef CONFIG_DEBUG_LOCK_ALLOC
164 * srcu_read_lock_held - might we be in SRCU read-side critical section?
166 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
167 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
168 * this assumes we are in an SRCU read-side critical section unless it can
171 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
172 * and while lockdep is disabled.
174 * Note that SRCU is based on its own statemachine and it doesn't
175 * relies on normal RCU, it can be called from the CPU which
176 * is in the idle loop from an RCU point of view or offline.
178 static inline int srcu_read_lock_held(struct srcu_struct *sp)
180 if (!debug_lockdep_rcu_enabled())
182 return lock_is_held(&sp->dep_map);
185 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
187 static inline int srcu_read_lock_held(struct srcu_struct *sp)
192 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
195 * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
196 * @p: the pointer to fetch and protect for later dereferencing
197 * @sp: pointer to the srcu_struct, which is used to check that we
198 * really are in an SRCU read-side critical section.
199 * @c: condition to check for update-side use
201 * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
202 * critical section will result in an RCU-lockdep splat, unless @c evaluates
203 * to 1. The @c argument will normally be a logical expression containing
204 * lockdep_is_held() calls.
206 #define srcu_dereference_check(p, sp, c) \
207 __rcu_dereference_check((p), (c) || srcu_read_lock_held(sp), __rcu)
210 * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
211 * @p: the pointer to fetch and protect for later dereferencing
212 * @sp: pointer to the srcu_struct, which is used to check that we
213 * really are in an SRCU read-side critical section.
215 * Makes rcu_dereference_check() do the dirty work. If PROVE_RCU
216 * is enabled, invoking this outside of an RCU read-side critical
217 * section will result in an RCU-lockdep splat.
219 #define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0)
222 * srcu_read_lock - register a new reader for an SRCU-protected structure.
223 * @sp: srcu_struct in which to register the new reader.
225 * Enter an SRCU read-side critical section. Note that SRCU read-side
226 * critical sections may be nested. However, it is illegal to
227 * call anything that waits on an SRCU grace period for the same
228 * srcu_struct, whether directly or indirectly. Please note that
229 * one way to indirectly wait on an SRCU grace period is to acquire
230 * a mutex that is held elsewhere while calling synchronize_srcu() or
231 * synchronize_srcu_expedited().
233 * Note that srcu_read_lock() and the matching srcu_read_unlock() must
234 * occur in the same context, for example, it is illegal to invoke
235 * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
236 * was invoked in process context.
238 static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
243 retval = __srcu_read_lock(sp);
245 rcu_lock_acquire(&(sp)->dep_map);
250 * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
251 * @sp: srcu_struct in which to unregister the old reader.
252 * @idx: return value from corresponding srcu_read_lock().
254 * Exit an SRCU read-side critical section.
256 static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
259 rcu_lock_release(&(sp)->dep_map);
260 __srcu_read_unlock(sp, idx);
264 * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
266 * Converts the preceding srcu_read_unlock into a two-way memory barrier.
268 * Call this after srcu_read_unlock, to guarantee that all memory operations
269 * that occur after smp_mb__after_srcu_read_unlock will appear to happen after
270 * the preceding srcu_read_unlock.
272 static inline void smp_mb__after_srcu_read_unlock(void)
274 /* __srcu_read_unlock has smp_mb() internally so nothing to do here. */