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>
35 #include <linux/rcu_segcblist.h>
38 unsigned long lock_count[2];
39 unsigned long unlock_count[2];
43 unsigned long completed;
44 unsigned long srcu_gp_seq;
45 struct srcu_array __percpu *per_cpu_ref;
46 spinlock_t queue_lock; /* protect ->srcu_cblist */
47 struct rcu_segcblist srcu_cblist;
48 struct delayed_work work;
49 #ifdef CONFIG_DEBUG_LOCK_ALLOC
50 struct lockdep_map dep_map;
51 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
54 /* Values for -> state variable. */
55 #define SRCU_STATE_IDLE 0
56 #define SRCU_STATE_SCAN1 1
57 #define SRCU_STATE_SCAN2 2
59 #ifdef CONFIG_DEBUG_LOCK_ALLOC
61 int __init_srcu_struct(struct srcu_struct *sp, const char *name,
62 struct lock_class_key *key);
64 #define init_srcu_struct(sp) \
66 static struct lock_class_key __srcu_key; \
68 __init_srcu_struct((sp), #sp, &__srcu_key); \
71 #define __SRCU_DEP_MAP_INIT(srcu_name) .dep_map = { .name = #srcu_name },
72 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
74 int init_srcu_struct(struct srcu_struct *sp);
76 #define __SRCU_DEP_MAP_INIT(srcu_name)
77 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
79 void process_srcu(struct work_struct *work);
81 #define __SRCU_STRUCT_INIT(name) \
84 .per_cpu_ref = &name##_srcu_array, \
85 .queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock), \
86 .srcu_cblist = RCU_SEGCBLIST_INITIALIZER(name.srcu_cblist),\
87 .work = __DELAYED_WORK_INITIALIZER(name.work, process_srcu, 0),\
88 __SRCU_DEP_MAP_INIT(name) \
92 * Define and initialize a srcu struct at build time.
93 * Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it.
95 * Note that although DEFINE_STATIC_SRCU() hides the name from other
96 * files, the per-CPU variable rules nevertheless require that the
97 * chosen name be globally unique. These rules also prohibit use of
98 * DEFINE_STATIC_SRCU() within a function. If these rules are too
99 * restrictive, declare the srcu_struct manually. For example, in
102 * static struct srcu_struct my_srcu;
104 * Then, before the first use of each my_srcu, manually initialize it:
106 * init_srcu_struct(&my_srcu);
108 * See include/linux/percpu-defs.h for the rules on per-CPU variables.
110 #define __DEFINE_SRCU(name, is_static) \
111 static DEFINE_PER_CPU(struct srcu_array, name##_srcu_array);\
112 is_static struct srcu_struct name = __SRCU_STRUCT_INIT(name)
113 #define DEFINE_SRCU(name) __DEFINE_SRCU(name, /* not static */)
114 #define DEFINE_STATIC_SRCU(name) __DEFINE_SRCU(name, static)
117 * call_srcu() - Queue a callback for invocation after an SRCU grace period
118 * @sp: srcu_struct in queue the callback
119 * @head: structure to be used for queueing the SRCU callback.
120 * @func: function to be invoked after the SRCU grace period
122 * The callback function will be invoked some time after a full SRCU
123 * grace period elapses, in other words after all pre-existing SRCU
124 * read-side critical sections have completed. However, the callback
125 * function might well execute concurrently with other SRCU read-side
126 * critical sections that started after call_srcu() was invoked. SRCU
127 * read-side critical sections are delimited by srcu_read_lock() and
128 * srcu_read_unlock(), and may be nested.
130 * The callback will be invoked from process context, but must nevertheless
131 * be fast and must not block.
133 void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
134 void (*func)(struct rcu_head *head));
136 void cleanup_srcu_struct(struct srcu_struct *sp);
137 int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
138 void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
139 void synchronize_srcu(struct srcu_struct *sp);
140 void synchronize_srcu_expedited(struct srcu_struct *sp);
141 unsigned long srcu_batches_completed(struct srcu_struct *sp);
142 void srcu_barrier(struct srcu_struct *sp);
144 #ifdef CONFIG_DEBUG_LOCK_ALLOC
147 * srcu_read_lock_held - might we be in SRCU read-side critical section?
149 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
150 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
151 * this assumes we are in an SRCU read-side critical section unless it can
154 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
155 * and while lockdep is disabled.
157 * Note that SRCU is based on its own statemachine and it doesn't
158 * relies on normal RCU, it can be called from the CPU which
159 * is in the idle loop from an RCU point of view or offline.
161 static inline int srcu_read_lock_held(struct srcu_struct *sp)
163 if (!debug_lockdep_rcu_enabled())
165 return lock_is_held(&sp->dep_map);
168 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
170 static inline int srcu_read_lock_held(struct srcu_struct *sp)
175 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
178 * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
179 * @p: the pointer to fetch and protect for later dereferencing
180 * @sp: pointer to the srcu_struct, which is used to check that we
181 * really are in an SRCU read-side critical section.
182 * @c: condition to check for update-side use
184 * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
185 * critical section will result in an RCU-lockdep splat, unless @c evaluates
186 * to 1. The @c argument will normally be a logical expression containing
187 * lockdep_is_held() calls.
189 #define srcu_dereference_check(p, sp, c) \
190 __rcu_dereference_check((p), (c) || srcu_read_lock_held(sp), __rcu)
193 * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
194 * @p: the pointer to fetch and protect for later dereferencing
195 * @sp: pointer to the srcu_struct, which is used to check that we
196 * really are in an SRCU read-side critical section.
198 * Makes rcu_dereference_check() do the dirty work. If PROVE_RCU
199 * is enabled, invoking this outside of an RCU read-side critical
200 * section will result in an RCU-lockdep splat.
202 #define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0)
205 * srcu_read_lock - register a new reader for an SRCU-protected structure.
206 * @sp: srcu_struct in which to register the new reader.
208 * Enter an SRCU read-side critical section. Note that SRCU read-side
209 * critical sections may be nested. However, it is illegal to
210 * call anything that waits on an SRCU grace period for the same
211 * srcu_struct, whether directly or indirectly. Please note that
212 * one way to indirectly wait on an SRCU grace period is to acquire
213 * a mutex that is held elsewhere while calling synchronize_srcu() or
214 * synchronize_srcu_expedited().
216 * Note that srcu_read_lock() and the matching srcu_read_unlock() must
217 * occur in the same context, for example, it is illegal to invoke
218 * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
219 * was invoked in process context.
221 static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
226 retval = __srcu_read_lock(sp);
228 rcu_lock_acquire(&(sp)->dep_map);
233 * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
234 * @sp: srcu_struct in which to unregister the old reader.
235 * @idx: return value from corresponding srcu_read_lock().
237 * Exit an SRCU read-side critical section.
239 static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
242 rcu_lock_release(&(sp)->dep_map);
243 __srcu_read_unlock(sp, idx);
247 * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
249 * Converts the preceding srcu_read_unlock into a two-way memory barrier.
251 * Call this after srcu_read_unlock, to guarantee that all memory operations
252 * that occur after smp_mb__after_srcu_read_unlock will appear to happen after
253 * the preceding srcu_read_unlock.
255 static inline void smp_mb__after_srcu_read_unlock(void)
257 /* __srcu_read_unlock has smp_mb() internally so nothing to do here. */