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, 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 #include <linux/rcu_segcblist.h>
  36
  37 struct srcu_struct;
  38
  39 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  40
  41 int __init_srcu_struct(struct srcu_struct *sp, const char *name,
  42                        struct lock_class_key *key);
  43
  44 #define init_srcu_struct(sp) \
  45 ({ \
  46         static struct lock_class_key __srcu_key; \
  47         \
  48         __init_srcu_struct((sp), #sp, &__srcu_key); \
  49 })
  50
  51 #define __SRCU_DEP_MAP_INIT(srcu_name)  .dep_map = { .name = #srcu_name },
  52 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  53
  54 int init_srcu_struct(struct srcu_struct *sp);
  55
  56 #define __SRCU_DEP_MAP_INIT(srcu_name)
  57 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  58
  59 #ifdef CONFIG_TINY_SRCU
  60 #include <linux/srcutiny.h>
  61 #elif defined(CONFIG_TREE_SRCU)
  62 #include <linux/srcutree.h>
  63 #elif defined(CONFIG_SRCU)
  64 #error "Unknown SRCU implementation specified to kernel configuration"
  65 #else
  66 /* Dummy definition for things like notifiers.  Actual use gets link error. */
  67 struct srcu_struct { };
  68 #endif
  69
  70 void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
  71                 void (*func)(struct rcu_head *head));
  72 void cleanup_srcu_struct(struct srcu_struct *sp);
  73 int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
  74 void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
  75 void synchronize_srcu(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 SRCU is based on its own statemachine and it doesn't
  91  * relies on normal RCU, it can be called from the CPU which
  92  * is in the idle loop from an RCU point of view or offline.
  93  */
  94 static inline int srcu_read_lock_held(struct srcu_struct *sp)
  95 {
  96         if (!debug_lockdep_rcu_enabled())
  97                 return 1;
  98         return lock_is_held(&sp->dep_map);
  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), (c) || srcu_read_lock_held(sp), __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  * Note that srcu_read_lock() and the matching srcu_read_unlock() must
 150  * occur in the same context, for example, it is illegal to invoke
 151  * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
 152  * was invoked in process context.
 153  */
 154 static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
 155 {
 156         int retval;
 157
 158         retval = __srcu_read_lock(sp);
 159         rcu_lock_acquire(&(sp)->dep_map);
 160         return retval;
 161 }
 162
 163 /**
 164  * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
 165  * @sp: srcu_struct in which to unregister the old reader.
 166  * @idx: return value from corresponding srcu_read_lock().
 167  *
 168  * Exit an SRCU read-side critical section.
 169  */
 170 static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
 171         __releases(sp)
 172 {
 173         rcu_lock_release(&(sp)->dep_map);
 174         __srcu_read_unlock(sp, idx);
 175 }
 176
 177 /**
 178  * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
 179  *
 180  * Converts the preceding srcu_read_unlock into a two-way memory barrier.
 181  *
 182  * Call this after srcu_read_unlock, to guarantee that all memory operations
 183  * that occur after smp_mb__after_srcu_read_unlock will appear to happen after
 184  * the preceding srcu_read_unlock.
 185  */
 186 static inline void smp_mb__after_srcu_read_unlock(void)
 187 {
 188         /* __srcu_read_unlock has smp_mb() internally so nothing to do here. */
 189 }
 190
 191 #endif