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, 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#include <linux/workqueue.h>
  33
  34struct srcu_struct_array {
  35        unsigned long c[2];
  36        unsigned long seq[2];
  37};
  38
  39struct rcu_batch {
  40        struct rcu_head *head, **tail;
  41};
  42
  43struct srcu_struct {
  44        unsigned completed;
  45        struct srcu_struct_array __percpu *per_cpu_ref;
  46        spinlock_t queue_lock; /* protect ->batch_queue, ->running */
  47        bool running;
  48        /* callbacks just queued */
  49        struct rcu_batch batch_queue;
  50        /* callbacks try to do the first check_zero */
  51        struct rcu_batch batch_check0;
  52        /* callbacks done with the first check_zero and the flip */
  53        struct rcu_batch batch_check1;
  54        struct rcu_batch batch_done;
  55        struct delayed_work work;
  56#ifdef CONFIG_DEBUG_LOCK_ALLOC
  57        struct lockdep_map dep_map;
  58#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  59};
  60
  61#ifdef CONFIG_DEBUG_LOCK_ALLOC
  62
  63int __init_srcu_struct(struct srcu_struct *sp, const char *name,
  64                       struct lock_class_key *key);
  65
  66#define init_srcu_struct(sp) \
  67({ \
  68        static struct lock_class_key __srcu_key; \
  69        \
  70        __init_srcu_struct((sp), #sp, &__srcu_key); \
  71})
  72
  73#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  74
  75int init_srcu_struct(struct srcu_struct *sp);
  76
  77#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  78
  79/**
  80 * call_srcu() - Queue a callback for invocation after an SRCU grace period
  81 * @sp: srcu_struct in queue the callback
  82 * @head: structure to be used for queueing the SRCU callback.
  83 * @func: function to be invoked after the SRCU grace period
  84 *
  85 * The callback function will be invoked some time after a full SRCU
  86 * grace period elapses, in other words after all pre-existing SRCU
  87 * read-side critical sections have completed.  However, the callback
  88 * function might well execute concurrently with other SRCU read-side
  89 * critical sections that started after call_srcu() was invoked.  SRCU
  90 * read-side critical sections are delimited by srcu_read_lock() and
  91 * srcu_read_unlock(), and may be nested.
  92 *
  93 * The callback will be invoked from process context, but must nevertheless
  94 * be fast and must not block.
  95 */
  96void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
  97                void (*func)(struct rcu_head *head));
  98
  99void cleanup_srcu_struct(struct srcu_struct *sp);
 100int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
 101void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
 102void synchronize_srcu(struct srcu_struct *sp);
 103void synchronize_srcu_expedited(struct srcu_struct *sp);
 104long srcu_batches_completed(struct srcu_struct *sp);
 105void srcu_barrier(struct srcu_struct *sp);
 106
 107#ifdef CONFIG_DEBUG_LOCK_ALLOC
 108
 109/**
 110 * srcu_read_lock_held - might we be in SRCU read-side critical section?
 111 *
 112 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
 113 * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
 114 * this assumes we are in an SRCU read-side critical section unless it can
 115 * prove otherwise.
 116 *
 117 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
 118 * and while lockdep is disabled.
 119 *
 120 * Note that if the CPU is in the idle loop from an RCU point of view
 121 * (ie: that we are in the section between rcu_idle_enter() and
 122 * rcu_idle_exit()) then srcu_read_lock_held() returns false even if
 123 * the CPU did an srcu_read_lock().  The reason for this is that RCU
 124 * ignores CPUs that are in such a section, considering these as in
 125 * extended quiescent state, so such a CPU is effectively never in an
 126 * RCU read-side critical section regardless of what RCU primitives it
 127 * invokes.  This state of affairs is required --- we need to keep an
 128 * RCU-free window in idle where the CPU may possibly enter into low
 129 * power mode. This way we can notice an extended quiescent state to
 130 * other CPUs that started a grace period. Otherwise we would delay any
 131 * grace period as long as we run in the idle task.
 132 *
 133 * Similarly, we avoid claiming an SRCU read lock held if the current
 134 * CPU is offline.
 135 */
 136static inline int srcu_read_lock_held(struct srcu_struct *sp)
 137{
 138        if (!debug_lockdep_rcu_enabled())
 139                return 1;
 140        if (rcu_is_cpu_idle())
 141                return 0;
 142        if (!rcu_lockdep_current_cpu_online())
 143                return 0;
 144        return lock_is_held(&sp->dep_map);
 145}
 146
 147#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 148
 149static inline int srcu_read_lock_held(struct srcu_struct *sp)
 150{
 151        return 1;
 152}
 153
 154#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 155
 156/**
 157 * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
 158 * @p: the pointer to fetch and protect for later dereferencing
 159 * @sp: pointer to the srcu_struct, which is used to check that we
 160 *      really are in an SRCU read-side critical section.
 161 * @c: condition to check for update-side use
 162 *
 163 * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
 164 * critical section will result in an RCU-lockdep splat, unless @c evaluates
 165 * to 1.  The @c argument will normally be a logical expression containing
 166 * lockdep_is_held() calls.
 167 */
 168#define srcu_dereference_check(p, sp, c) \
 169        __rcu_dereference_check((p), srcu_read_lock_held(sp) || (c), __rcu)
 170
 171/**
 172 * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
 173 * @p: the pointer to fetch and protect for later dereferencing
 174 * @sp: pointer to the srcu_struct, which is used to check that we
 175 *      really are in an SRCU read-side critical section.
 176 *
 177 * Makes rcu_dereference_check() do the dirty work.  If PROVE_RCU
 178 * is enabled, invoking this outside of an RCU read-side critical
 179 * section will result in an RCU-lockdep splat.
 180 */
 181#define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0)
 182
 183/**
 184 * srcu_read_lock - register a new reader for an SRCU-protected structure.
 185 * @sp: srcu_struct in which to register the new reader.
 186 *
 187 * Enter an SRCU read-side critical section.  Note that SRCU read-side
 188 * critical sections may be nested.  However, it is illegal to
 189 * call anything that waits on an SRCU grace period for the same
 190 * srcu_struct, whether directly or indirectly.  Please note that
 191 * one way to indirectly wait on an SRCU grace period is to acquire
 192 * a mutex that is held elsewhere while calling synchronize_srcu() or
 193 * synchronize_srcu_expedited().
 194 *
 195 * Note that srcu_read_lock() and the matching srcu_read_unlock() must
 196 * occur in the same context, for example, it is illegal to invoke
 197 * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
 198 * was invoked in process context.
 199 */
 200static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
 201{
 202        int retval = __srcu_read_lock(sp);
 203
 204        rcu_lock_acquire(&(sp)->dep_map);
 205        rcu_lockdep_assert(!rcu_is_cpu_idle(),
 206                           "srcu_read_lock() used illegally while idle");
 207        return retval;
 208}
 209
 210/**
 211 * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
 212 * @sp: srcu_struct in which to unregister the old reader.
 213 * @idx: return value from corresponding srcu_read_lock().
 214 *
 215 * Exit an SRCU read-side critical section.
 216 */
 217static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
 218        __releases(sp)
 219{
 220        rcu_lockdep_assert(!rcu_is_cpu_idle(),
 221                           "srcu_read_unlock() used illegally while idle");
 222        rcu_lock_release(&(sp)->dep_map);
 223        __srcu_read_unlock(sp, idx);
 224}
 225
 226/**
 227 * srcu_read_lock_raw - register a new reader for an SRCU-protected structure.
 228 * @sp: srcu_struct in which to register the new reader.
 229 *
 230 * Enter an SRCU read-side critical section.  Similar to srcu_read_lock(),
 231 * but avoids the RCU-lockdep checking.  This means that it is legal to
 232 * use srcu_read_lock_raw() in one context, for example, in an exception
 233 * handler, and then have the matching srcu_read_unlock_raw() in another
 234 * context, for example in the task that took the exception.
 235 *
 236 * However, the entire SRCU read-side critical section must reside within a
 237 * single task.  For example, beware of using srcu_read_lock_raw() in
 238 * a device interrupt handler and srcu_read_unlock() in the interrupted
 239 * task:  This will not work if interrupts are threaded.
 240 */
 241static inline int srcu_read_lock_raw(struct srcu_struct *sp)
 242{
 243        unsigned long flags;
 244        int ret;
 245
 246        local_irq_save(flags);
 247        ret =  __srcu_read_lock(sp);
 248        local_irq_restore(flags);
 249        return ret;
 250}
 251
 252/**
 253 * srcu_read_unlock_raw - unregister reader from an SRCU-protected structure.
 254 * @sp: srcu_struct in which to unregister the old reader.
 255 * @idx: return value from corresponding srcu_read_lock_raw().
 256 *
 257 * Exit an SRCU read-side critical section without lockdep-RCU checking.
 258 * See srcu_read_lock_raw() for more details.
 259 */
 260static inline void srcu_read_unlock_raw(struct srcu_struct *sp, int idx)
 261{
 262        unsigned long flags;
 263
 264        local_irq_save(flags);
 265        __srcu_read_unlock(sp, idx);
 266        local_irq_restore(flags);
 267}
 268
 269#endif
 270
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