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/include/linux/srcu.h

https://github.com/airy09/android_kernel_sony_apq8064
C Header | 239 lines | 91 code | 27 blank | 121 comment | 4 complexity | 8c2aa0f9ddb62e2c871e124d635849d4 MD5 | raw file
  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, write to the Free Software
 16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 17 *
 18 * Copyright (C) IBM Corporation, 2006
 19 *
 20 * Author: Paul McKenney <paulmck@us.ibm.com>
 21 *
 22 * For detailed explanation of Read-Copy Update mechanism see -
 23 * 		Documentation/RCU/ *.txt
 24 *
 25 */
 26
 27#ifndef _LINUX_SRCU_H
 28#define _LINUX_SRCU_H
 29
 30#include <linux/mutex.h>
 31#include <linux/rcupdate.h>
 32
 33struct srcu_struct_array {
 34	int c[2];
 35};
 36
 37struct srcu_struct {
 38	int completed;
 39	struct srcu_struct_array __percpu *per_cpu_ref;
 40	struct mutex mutex;
 41#ifdef CONFIG_DEBUG_LOCK_ALLOC
 42	struct lockdep_map dep_map;
 43#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 44};
 45
 46#ifndef CONFIG_PREEMPT
 47#define srcu_barrier() barrier()
 48#else /* #ifndef CONFIG_PREEMPT */
 49#define srcu_barrier()
 50#endif /* #else #ifndef CONFIG_PREEMPT */
 51
 52#ifdef CONFIG_DEBUG_LOCK_ALLOC
 53
 54int __init_srcu_struct(struct srcu_struct *sp, const char *name,
 55		       struct lock_class_key *key);
 56
 57#define init_srcu_struct(sp) \
 58({ \
 59	static struct lock_class_key __srcu_key; \
 60	\
 61	__init_srcu_struct((sp), #sp, &__srcu_key); \
 62})
 63
 64#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 65
 66int init_srcu_struct(struct srcu_struct *sp);
 67
 68#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 69
 70void cleanup_srcu_struct(struct srcu_struct *sp);
 71int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
 72void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
 73void synchronize_srcu(struct srcu_struct *sp);
 74void synchronize_srcu_expedited(struct srcu_struct *sp);
 75long srcu_batches_completed(struct srcu_struct *sp);
 76
 77#ifdef CONFIG_DEBUG_LOCK_ALLOC
 78
 79/**
 80 * srcu_read_lock_held - might we be in SRCU read-side critical section?
 81 *
 82 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
 83 * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
 84 * this assumes we are in an SRCU read-side critical section unless it can
 85 * prove otherwise.
 86 *
 87 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
 88 * and while lockdep is disabled.
 89 *
 90 * Note that if the CPU is in the idle loop from an RCU point of view
 91 * (ie: that we are in the section between rcu_idle_enter() and
 92 * rcu_idle_exit()) then srcu_read_lock_held() returns false even if
 93 * the CPU did an srcu_read_lock().  The reason for this is that RCU
 94 * ignores CPUs that are in such a section, considering these as in
 95 * extended quiescent state, so such a CPU is effectively never in an
 96 * RCU read-side critical section regardless of what RCU primitives it
 97 * invokes.  This state of affairs is required --- we need to keep an
 98 * RCU-free window in idle where the CPU may possibly enter into low
 99 * power mode. This way we can notice an extended quiescent state to
100 * other CPUs that started a grace period. Otherwise we would delay any
101 * grace period as long as we run in the idle task.
102 *
103 * Similarly, we avoid claiming an SRCU read lock held if the current
104 * CPU is offline.
105 */
106static inline int srcu_read_lock_held(struct srcu_struct *sp)
107{
108	if (!debug_lockdep_rcu_enabled())
109		return 1;
110	if (rcu_is_cpu_idle())
111		return 0;
112	if (!rcu_lockdep_current_cpu_online())
113		return 0;
114	return lock_is_held(&sp->dep_map);
115}
116
117#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
118
119static inline int srcu_read_lock_held(struct srcu_struct *sp)
120{
121	return 1;
122}
123
124#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
125
126/**
127 * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
128 * @p: the pointer to fetch and protect for later dereferencing
129 * @sp: pointer to the srcu_struct, which is used to check that we
130 *	really are in an SRCU read-side critical section.
131 * @c: condition to check for update-side use
132 *
133 * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
134 * critical section will result in an RCU-lockdep splat, unless @c evaluates
135 * to 1.  The @c argument will normally be a logical expression containing
136 * lockdep_is_held() calls.
137 */
138#define srcu_dereference_check(p, sp, c) \
139	__rcu_dereference_check((p), srcu_read_lock_held(sp) || (c), __rcu)
140
141/**
142 * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
143 * @p: the pointer to fetch and protect for later dereferencing
144 * @sp: pointer to the srcu_struct, which is used to check that we
145 *	really are in an SRCU read-side critical section.
146 *
147 * Makes rcu_dereference_check() do the dirty work.  If PROVE_RCU
148 * is enabled, invoking this outside of an RCU read-side critical
149 * section will result in an RCU-lockdep splat.
150 */
151#define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0)
152
153/**
154 * srcu_read_lock - register a new reader for an SRCU-protected structure.
155 * @sp: srcu_struct in which to register the new reader.
156 *
157 * Enter an SRCU read-side critical section.  Note that SRCU read-side
158 * critical sections may be nested.  However, it is illegal to
159 * call anything that waits on an SRCU grace period for the same
160 * srcu_struct, whether directly or indirectly.  Please note that
161 * one way to indirectly wait on an SRCU grace period is to acquire
162 * a mutex that is held elsewhere while calling synchronize_srcu() or
163 * synchronize_srcu_expedited().
164 *
165 * Note that srcu_read_lock() and the matching srcu_read_unlock() must
166 * occur in the same context, for example, it is illegal to invoke
167 * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
168 * was invoked in process context.
169 */
170static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
171{
172	int retval = __srcu_read_lock(sp);
173
174	rcu_lock_acquire(&(sp)->dep_map);
175	rcu_lockdep_assert(!rcu_is_cpu_idle(),
176			   "srcu_read_lock() used illegally while idle");
177	return retval;
178}
179
180/**
181 * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
182 * @sp: srcu_struct in which to unregister the old reader.
183 * @idx: return value from corresponding srcu_read_lock().
184 *
185 * Exit an SRCU read-side critical section.
186 */
187static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
188	__releases(sp)
189{
190	rcu_lockdep_assert(!rcu_is_cpu_idle(),
191			   "srcu_read_unlock() used illegally while idle");
192	rcu_lock_release(&(sp)->dep_map);
193	__srcu_read_unlock(sp, idx);
194}
195
196/**
197 * srcu_read_lock_raw - register a new reader for an SRCU-protected structure.
198 * @sp: srcu_struct in which to register the new reader.
199 *
200 * Enter an SRCU read-side critical section.  Similar to srcu_read_lock(),
201 * but avoids the RCU-lockdep checking.  This means that it is legal to
202 * use srcu_read_lock_raw() in one context, for example, in an exception
203 * handler, and then have the matching srcu_read_unlock_raw() in another
204 * context, for example in the task that took the exception.
205 *
206 * However, the entire SRCU read-side critical section must reside within a
207 * single task.  For example, beware of using srcu_read_lock_raw() in
208 * a device interrupt handler and srcu_read_unlock() in the interrupted
209 * task:  This will not work if interrupts are threaded.
210 */
211static inline int srcu_read_lock_raw(struct srcu_struct *sp)
212{
213	unsigned long flags;
214	int ret;
215
216	local_irq_save(flags);
217	ret =  __srcu_read_lock(sp);
218	local_irq_restore(flags);
219	return ret;
220}
221
222/**
223 * srcu_read_unlock_raw - unregister reader from an SRCU-protected structure.
224 * @sp: srcu_struct in which to unregister the old reader.
225 * @idx: return value from corresponding srcu_read_lock_raw().
226 *
227 * Exit an SRCU read-side critical section without lockdep-RCU checking.
228 * See srcu_read_lock_raw() for more details.
229 */
230static inline void srcu_read_unlock_raw(struct srcu_struct *sp, int idx)
231{
232	unsigned long flags;
233
234	local_irq_save(flags);
235	__srcu_read_unlock(sp, idx);
236	local_irq_restore(flags);
237}
238
239#endif