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, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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>
36 struct srcu_struct_array {
42 struct rcu_head *head, **tail;
47 struct srcu_struct_array __percpu *per_cpu_ref;
48 spinlock_t queue_lock; /* protect ->batch_queue, ->running */
50 /* callbacks just queued */
51 struct rcu_batch batch_queue;
52 /* callbacks try to do the first check_zero */
53 struct rcu_batch batch_check0;
54 /* callbacks done with the first check_zero and the flip */
55 struct rcu_batch batch_check1;
56 struct rcu_batch batch_done;
57 struct delayed_work work;
58 #ifdef CONFIG_DEBUG_LOCK_ALLOC
59 struct lockdep_map dep_map;
60 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
63 #ifdef CONFIG_DEBUG_LOCK_ALLOC
65 int __init_srcu_struct(struct srcu_struct *sp, const char *name,
66 struct lock_class_key *key);
68 #define init_srcu_struct(sp) \
70 static struct lock_class_key __srcu_key; \
72 __init_srcu_struct((sp), #sp, &__srcu_key); \
75 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
77 int init_srcu_struct(struct srcu_struct *sp);
79 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
82 * call_srcu() - Queue a callback for invocation after an SRCU grace period
83 * @sp: srcu_struct in queue the callback
84 * @head: structure to be used for queueing the SRCU callback.
85 * @func: function to be invoked after the SRCU grace period
87 * The callback function will be invoked some time after a full SRCU
88 * grace period elapses, in other words after all pre-existing SRCU
89 * read-side critical sections have completed. However, the callback
90 * function might well execute concurrently with other SRCU read-side
91 * critical sections that started after call_srcu() was invoked. SRCU
92 * read-side critical sections are delimited by srcu_read_lock() and
93 * srcu_read_unlock(), and may be nested.
95 * The callback will be invoked from process context, but must nevertheless
96 * be fast and must not block.
98 void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
99 void (*func)(struct rcu_head *head));
101 void cleanup_srcu_struct(struct srcu_struct *sp);
102 int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
103 void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
104 void synchronize_srcu(struct srcu_struct *sp);
105 void synchronize_srcu_expedited(struct srcu_struct *sp);
106 long srcu_batches_completed(struct srcu_struct *sp);
107 void srcu_barrier(struct srcu_struct *sp);
109 #ifdef CONFIG_DEBUG_LOCK_ALLOC
112 * srcu_read_lock_held - might we be in SRCU read-side critical section?
114 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
115 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
116 * this assumes we are in an SRCU read-side critical section unless it can
119 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
120 * and while lockdep is disabled.
122 * Note that if the CPU is in the idle loop from an RCU point of view
123 * (ie: that we are in the section between rcu_idle_enter() and
124 * rcu_idle_exit()) then srcu_read_lock_held() returns false even if
125 * the CPU did an srcu_read_lock(). The reason for this is that RCU
126 * ignores CPUs that are in such a section, considering these as in
127 * extended quiescent state, so such a CPU is effectively never in an
128 * RCU read-side critical section regardless of what RCU primitives it
129 * invokes. This state of affairs is required --- we need to keep an
130 * RCU-free window in idle where the CPU may possibly enter into low
131 * power mode. This way we can notice an extended quiescent state to
132 * other CPUs that started a grace period. Otherwise we would delay any
133 * grace period as long as we run in the idle task.
135 * Similarly, we avoid claiming an SRCU read lock held if the current
138 static inline int srcu_read_lock_held(struct srcu_struct *sp)
140 if (!debug_lockdep_rcu_enabled())
142 if (rcu_is_cpu_idle())
144 if (!rcu_lockdep_current_cpu_online())
146 return lock_is_held(&sp->dep_map);
149 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
151 static inline int srcu_read_lock_held(struct srcu_struct *sp)
156 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
159 * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
160 * @p: the pointer to fetch and protect for later dereferencing
161 * @sp: pointer to the srcu_struct, which is used to check that we
162 * really are in an SRCU read-side critical section.
163 * @c: condition to check for update-side use
165 * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
166 * critical section will result in an RCU-lockdep splat, unless @c evaluates
167 * to 1. The @c argument will normally be a logical expression containing
168 * lockdep_is_held() calls.
170 #define srcu_dereference_check(p, sp, c) \
171 __rcu_dereference_check((p), srcu_read_lock_held(sp) || (c), __rcu)
174 * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
175 * @p: the pointer to fetch and protect for later dereferencing
176 * @sp: pointer to the srcu_struct, which is used to check that we
177 * really are in an SRCU read-side critical section.
179 * Makes rcu_dereference_check() do the dirty work. If PROVE_RCU
180 * is enabled, invoking this outside of an RCU read-side critical
181 * section will result in an RCU-lockdep splat.
183 #define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0)
186 * srcu_read_lock - register a new reader for an SRCU-protected structure.
187 * @sp: srcu_struct in which to register the new reader.
189 * Enter an SRCU read-side critical section. Note that SRCU read-side
190 * critical sections may be nested. However, it is illegal to
191 * call anything that waits on an SRCU grace period for the same
192 * srcu_struct, whether directly or indirectly. Please note that
193 * one way to indirectly wait on an SRCU grace period is to acquire
194 * a mutex that is held elsewhere while calling synchronize_srcu() or
195 * synchronize_srcu_expedited().
197 * Note that srcu_read_lock() and the matching srcu_read_unlock() must
198 * occur in the same context, for example, it is illegal to invoke
199 * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
200 * was invoked in process context.
202 static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
204 int retval = __srcu_read_lock(sp);
206 rcu_lock_acquire(&(sp)->dep_map);
207 rcu_lockdep_assert(!rcu_is_cpu_idle(),
208 "srcu_read_lock() used illegally while idle");
213 * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
214 * @sp: srcu_struct in which to unregister the old reader.
215 * @idx: return value from corresponding srcu_read_lock().
217 * Exit an SRCU read-side critical section.
219 static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
222 rcu_lockdep_assert(!rcu_is_cpu_idle(),
223 "srcu_read_unlock() used illegally while idle");
224 rcu_lock_release(&(sp)->dep_map);
225 __srcu_read_unlock(sp, idx);
229 * srcu_read_lock_raw - register a new reader for an SRCU-protected structure.
230 * @sp: srcu_struct in which to register the new reader.
232 * Enter an SRCU read-side critical section. Similar to srcu_read_lock(),
233 * but avoids the RCU-lockdep checking. This means that it is legal to
234 * use srcu_read_lock_raw() in one context, for example, in an exception
235 * handler, and then have the matching srcu_read_unlock_raw() in another
236 * context, for example in the task that took the exception.
238 * However, the entire SRCU read-side critical section must reside within a
239 * single task. For example, beware of using srcu_read_lock_raw() in
240 * a device interrupt handler and srcu_read_unlock() in the interrupted
241 * task: This will not work if interrupts are threaded.
243 static inline int srcu_read_lock_raw(struct srcu_struct *sp)
248 local_irq_save(flags);
249 ret = __srcu_read_lock(sp);
250 local_irq_restore(flags);
255 * srcu_read_unlock_raw - unregister reader from an SRCU-protected structure.
256 * @sp: srcu_struct in which to unregister the old reader.
257 * @idx: return value from corresponding srcu_read_lock_raw().
259 * Exit an SRCU read-side critical section without lockdep-RCU checking.
260 * See srcu_read_lock_raw() for more details.
262 static inline void srcu_read_unlock_raw(struct srcu_struct *sp, int idx)
266 local_irq_save(flags);
267 __srcu_read_unlock(sp, idx);
268 local_irq_restore(flags);