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 * 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
  36struct srcu_struct_array {
  37        unsigned long c[2];
  38        unsigned long seq[2];
  39};
  40
  41struct rcu_batch {
  42        struct rcu_head *head, **tail;
  43};
  44
  45#define RCU_BATCH_INIT(name) { NULL, &(name.head) }
  46
  47struct srcu_struct {
  48        unsigned completed;
  49        struct srcu_struct_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
  67int __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
  80int 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
  85void 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 init a srcu struct at build time.
 103 * dont't call init_srcu_struct() nor cleanup_srcu_struct() on it.
 104 */
 105#define DEFINE_SRCU(name)                                               \
 106        static DEFINE_PER_CPU(struct srcu_struct_array, name##_srcu_array);\
 107        struct srcu_struct name = __SRCU_STRUCT_INIT(name);
 108
 109#define DEFINE_STATIC_SRCU(name)                                        \
 110        static DEFINE_PER_CPU(struct srcu_struct_array, name##_srcu_array);\
 111        static struct srcu_struct name = __SRCU_STRUCT_INIT(name);
 112
 113/**
 114 * call_srcu() - Queue a callback for invocation after an SRCU grace period
 115 * @sp: srcu_struct in queue the callback
 116 * @head: structure to be used for queueing the SRCU callback.
 117 * @func: function to be invoked after the SRCU grace period
 118 *
 119 * The callback function will be invoked some time after a full SRCU
 120 * grace period elapses, in other words after all pre-existing SRCU
 121 * read-side critical sections have completed.  However, the callback
 122 * function might well execute concurrently with other SRCU read-side
 123 * critical sections that started after call_srcu() was invoked.  SRCU
 124 * read-side critical sections are delimited by srcu_read_lock() and
 125 * srcu_read_unlock(), and may be nested.
 126 *
 127 * The callback will be invoked from process context, but must nevertheless
 128 * be fast and must not block.
 129 */
 130void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
 131                void (*func)(struct rcu_head *head));
 132
 133void cleanup_srcu_struct(struct srcu_struct *sp);
 134int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
 135void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
 136void synchronize_srcu(struct srcu_struct *sp);
 137void synchronize_srcu_expedited(struct srcu_struct *sp);
 138long srcu_batches_completed(struct srcu_struct *sp);
 139void srcu_barrier(struct srcu_struct *sp);
 140
 141#ifdef CONFIG_DEBUG_LOCK_ALLOC
 142
 143/**
 144 * srcu_read_lock_held - might we be in SRCU read-side critical section?
 145 *
 146 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
 147 * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
 148 * this assumes we are in an SRCU read-side critical section unless it can
 149 * prove otherwise.
 150 *
 151 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
 152 * and while lockdep is disabled.
 153 *
 154 * Note that if the CPU is in the idle loop from an RCU point of view
 155 * (ie: that we are in the section between rcu_idle_enter() and
 156 * rcu_idle_exit()) then srcu_read_lock_held() returns false even if
 157 * the CPU did an srcu_read_lock().  The reason for this is that RCU
 158 * ignores CPUs that are in such a section, considering these as in
 159 * extended quiescent state, so such a CPU is effectively never in an
 160 * RCU read-side critical section regardless of what RCU primitives it
 161 * invokes.  This state of affairs is required --- we need to keep an
 162 * RCU-free window in idle where the CPU may possibly enter into low
 163 * power mode. This way we can notice an extended quiescent state to
 164 * other CPUs that started a grace period. Otherwise we would delay any
 165 * grace period as long as we run in the idle task.
 166 *
 167 * Similarly, we avoid claiming an SRCU read lock held if the current
 168 * CPU is offline.
 169 */
 170static inline int srcu_read_lock_held(struct srcu_struct *sp)
 171{
 172        if (!debug_lockdep_rcu_enabled())
 173                return 1;
 174        if (rcu_is_cpu_idle())
 175                return 0;
 176        if (!rcu_lockdep_current_cpu_online())
 177                return 0;
 178        return lock_is_held(&sp->dep_map);
 179}
 180
 181#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 182
 183static inline int srcu_read_lock_held(struct srcu_struct *sp)
 184{
 185        return 1;
 186}
 187
 188#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 189
 190/**
 191 * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
 192 * @p: the pointer to fetch and protect for later dereferencing
 193 * @sp: pointer to the srcu_struct, which is used to check that we
 194 *      really are in an SRCU read-side critical section.
 195 * @c: condition to check for update-side use
 196 *
 197 * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
 198 * critical section will result in an RCU-lockdep splat, unless @c evaluates
 199 * to 1.  The @c argument will normally be a logical expression containing
 200 * lockdep_is_held() calls.
 201 */
 202#define srcu_dereference_check(p, sp, c) \
 203        __rcu_dereference_check((p), srcu_read_lock_held(sp) || (c), __rcu)
 204
 205/**
 206 * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
 207 * @p: the pointer to fetch and protect for later dereferencing
 208 * @sp: pointer to the srcu_struct, which is used to check that we
 209 *      really are in an SRCU read-side critical section.
 210 *
 211 * Makes rcu_dereference_check() do the dirty work.  If PROVE_RCU
 212 * is enabled, invoking this outside of an RCU read-side critical
 213 * section will result in an RCU-lockdep splat.
 214 */
 215#define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0)
 216
 217/**
 218 * srcu_read_lock - register a new reader for an SRCU-protected structure.
 219 * @sp: srcu_struct in which to register the new reader.
 220 *
 221 * Enter an SRCU read-side critical section.  Note that SRCU read-side
 222 * critical sections may be nested.  However, it is illegal to
 223 * call anything that waits on an SRCU grace period for the same
 224 * srcu_struct, whether directly or indirectly.  Please note that
 225 * one way to indirectly wait on an SRCU grace period is to acquire
 226 * a mutex that is held elsewhere while calling synchronize_srcu() or
 227 * synchronize_srcu_expedited().
 228 *
 229 * Note that srcu_read_lock() and the matching srcu_read_unlock() must
 230 * occur in the same context, for example, it is illegal to invoke
 231 * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
 232 * was invoked in process context.
 233 */
 234static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
 235{
 236        int retval = __srcu_read_lock(sp);
 237
 238        rcu_lock_acquire(&(sp)->dep_map);
 239        rcu_lockdep_assert(!rcu_is_cpu_idle(),
 240                           "srcu_read_lock() used illegally while idle");
 241        return retval;
 242}
 243
 244/**
 245 * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
 246 * @sp: srcu_struct in which to unregister the old reader.
 247 * @idx: return value from corresponding srcu_read_lock().
 248 *
 249 * Exit an SRCU read-side critical section.
 250 */
 251static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
 252        __releases(sp)
 253{
 254        rcu_lockdep_assert(!rcu_is_cpu_idle(),
 255                           "srcu_read_unlock() used illegally while idle");
 256        rcu_lock_release(&(sp)->dep_map);
 257        __srcu_read_unlock(sp, idx);
 258}
 259
 260/**
 261 * srcu_read_lock_raw - register a new reader for an SRCU-protected structure.
 262 * @sp: srcu_struct in which to register the new reader.
 263 *
 264 * Enter an SRCU read-side critical section.  Similar to srcu_read_lock(),
 265 * but avoids the RCU-lockdep checking.  This means that it is legal to
 266 * use srcu_read_lock_raw() in one context, for example, in an exception
 267 * handler, and then have the matching srcu_read_unlock_raw() in another
 268 * context, for example in the task that took the exception.
 269 *
 270 * However, the entire SRCU read-side critical section must reside within a
 271 * single task.  For example, beware of using srcu_read_lock_raw() in
 272 * a device interrupt handler and srcu_read_unlock() in the interrupted
 273 * task:  This will not work if interrupts are threaded.
 274 */
 275static inline int srcu_read_lock_raw(struct srcu_struct *sp)
 276{
 277        unsigned long flags;
 278        int ret;
 279
 280        local_irq_save(flags);
 281        ret =  __srcu_read_lock(sp);
 282        local_irq_restore(flags);
 283        return ret;
 284}
 285
 286/**
 287 * srcu_read_unlock_raw - unregister reader from an SRCU-protected structure.
 288 * @sp: srcu_struct in which to unregister the old reader.
 289 * @idx: return value from corresponding srcu_read_lock_raw().
 290 *
 291 * Exit an SRCU read-side critical section without lockdep-RCU checking.
 292 * See srcu_read_lock_raw() for more details.
 293 */
 294static inline void srcu_read_unlock_raw(struct srcu_struct *sp, int idx)
 295{
 296        unsigned long flags;
 297
 298        local_irq_save(flags);
 299        __srcu_read_unlock(sp, idx);
 300        local_irq_restore(flags);
 301}
 302
 303#endif
 304
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