include/linux/srcu.h

   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
  32 struct srcu_struct_array {
  33         int c[2];
  34 };
  35
  36 struct srcu_struct {
  37         int completed;
  38         struct srcu_struct_array __percpu *per_cpu_ref;
  39         struct mutex mutex;
  40 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  41         struct lockdep_map dep_map;
  42 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  43 };
  44
  45 #ifndef CONFIG_PREEMPT
  46 #define srcu_barrier() barrier()
  47 #else /* #ifndef CONFIG_PREEMPT */
  48 #define srcu_barrier()
  49 #endif /* #else #ifndef CONFIG_PREEMPT */
  50
  51 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  52
  53 int __init_srcu_struct(struct srcu_struct *sp, const char *name,
  54                        struct lock_class_key *key);
  55
  56 #define init_srcu_struct(sp) \
  57 ({ \
  58         static struct lock_class_key __srcu_key; \
  59         \
  60         __init_srcu_struct((sp), #sp, &__srcu_key); \
  61 })
  62
  63 # define srcu_read_acquire(sp) \
  64                 lock_acquire(&(sp)->dep_map, 0, 0, 2, 1, NULL, _THIS_IP_)
  65 # define srcu_read_release(sp) \
  66                 lock_release(&(sp)->dep_map, 1, _THIS_IP_)
  67
  68 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  69
  70 int init_srcu_struct(struct srcu_struct *sp);
  71
  72 # define srcu_read_acquire(sp)  do { } while (0)
  73 # define srcu_read_release(sp)  do { } while (0)
  74
  75 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  76
  77 void cleanup_srcu_struct(struct srcu_struct *sp);
  78 int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
  79 void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
  80 void synchronize_srcu(struct srcu_struct *sp);
  81 void synchronize_srcu_expedited(struct srcu_struct *sp);
  82 long srcu_batches_completed(struct srcu_struct *sp);
  83
  84 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  85
  86 /**
  87  * srcu_read_lock_held - might we be in SRCU read-side critical section?
  88  *
  89  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
  90  * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
  91  * this assumes we are in an SRCU read-side critical section unless it can
  92  * prove otherwise.
  93  */
  94 static inline int srcu_read_lock_held(struct srcu_struct *sp)
  95 {
  96         if (debug_locks)
  97                 return lock_is_held(&sp->dep_map);
  98         return 1;
  99 }
 100
 101 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 102
 103 static inline int srcu_read_lock_held(struct srcu_struct *sp)
 104 {
 105         return 1;
 106 }
 107
 108 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 109
 110 /**
 111  * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
 112  * @p: the pointer to fetch and protect for later dereferencing
 113  * @sp: pointer to the srcu_struct, which is used to check that we
 114  *      really are in an SRCU read-side critical section.
 115  * @c: condition to check for update-side use
 116  *
 117  * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
 118  * critical section will result in an RCU-lockdep splat, unless @c evaluates
 119  * to 1.  The @c argument will normally be a logical expression containing
 120  * lockdep_is_held() calls.
 121  */
 122 #define srcu_dereference_check(p, sp, c) \
 123         __rcu_dereference_check((p), srcu_read_lock_held(sp) || (c), __rcu)
 124
 125 /**
 126  * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
 127  * @p: the pointer to fetch and protect for later dereferencing
 128  * @sp: pointer to the srcu_struct, which is used to check that we
 129  *      really are in an SRCU read-side critical section.
 130  *
 131  * Makes rcu_dereference_check() do the dirty work.  If PROVE_RCU
 132  * is enabled, invoking this outside of an RCU read-side critical
 133  * section will result in an RCU-lockdep splat.
 134  */
 135 #define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0)
 136
 137 /**
 138  * srcu_read_lock - register a new reader for an SRCU-protected structure.
 139  * @sp: srcu_struct in which to register the new reader.
 140  *
 141  * Enter an SRCU read-side critical section.  Note that SRCU read-side
 142  * critical sections may be nested.  However, it is illegal to
 143  * call anything that waits on an SRCU grace period for the same
 144  * srcu_struct, whether directly or indirectly.  Please note that
 145  * one way to indirectly wait on an SRCU grace period is to acquire
 146  * a mutex that is held elsewhere while calling synchronize_srcu() or
 147  * synchronize_srcu_expedited().
 148  */
 149 static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
 150 {
 151         int retval = __srcu_read_lock(sp);
 152
 153         srcu_read_acquire(sp);
 154         return retval;
 155 }
 156
 157 /**
 158  * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
 159  * @sp: srcu_struct in which to unregister the old reader.
 160  * @idx: return value from corresponding srcu_read_lock().
 161  *
 162  * Exit an SRCU read-side critical section.
 163  */
 164 static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
 165         __releases(sp)
 166 {
 167         srcu_read_release(sp);
 168         __srcu_read_unlock(sp, idx);
 169 }
 170
 171 #endif