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Linux/include/linux/srcu.h

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  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_array {
 37         unsigned long lock_count[2];
 38         unsigned long unlock_count[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_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_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  */
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 
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  */
231 static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
232 {
233         int retval;
234 
235         retval = __srcu_read_lock(sp);
236         rcu_lock_acquire(&(sp)->dep_map);
237         return retval;
238 }
239 
240 /**
241  * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
242  * @sp: srcu_struct in which to unregister the old reader.
243  * @idx: return value from corresponding srcu_read_lock().
244  *
245  * Exit an SRCU read-side critical section.
246  */
247 static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
248         __releases(sp)
249 {
250         rcu_lock_release(&(sp)->dep_map);
251         __srcu_read_unlock(sp, idx);
252 }
253 
254 /**
255  * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
256  *
257  * Converts the preceding srcu_read_unlock into a two-way memory barrier.
258  *
259  * Call this after srcu_read_unlock, to guarantee that all memory operations
260  * that occur after smp_mb__after_srcu_read_unlock will appear to happen after
261  * the preceding srcu_read_unlock.
262  */
263 static inline void smp_mb__after_srcu_read_unlock(void)
264 {
265         /* __srcu_read_unlock has smp_mb() internally so nothing to do here. */
266 }
267 
268 #endif
269 

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