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  * @sp: The srcu_struct structure to check
  82  *
  83  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
  84  * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
  85  * this assumes we are in an SRCU read-side critical section unless it can
  86  * prove otherwise.
  87  *
  88  * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
  89  * and while lockdep is disabled.
  90  *
  91  * Note that SRCU is based on its own statemachine and it doesn't
  92  * relies on normal RCU, it can be called from the CPU which
  93  * is in the idle loop from an RCU point of view or offline.
  94  */
  95 static inline int srcu_read_lock_held(struct srcu_struct *sp)
  96 {
  97         if (!debug_lockdep_rcu_enabled())
  98                 return 1;
  99         return lock_is_held(&sp->dep_map);
 100 }
 101
 102 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 103
 104 static inline int srcu_read_lock_held(struct srcu_struct *sp)
 105 {
 106         return 1;
 107 }
 108
 109 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 110
 111 /**
 112  * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
 113  * @p: the pointer to fetch and protect for later dereferencing
 114  * @sp: pointer to the srcu_struct, which is used to check that we
 115  *      really are in an SRCU read-side critical section.
 116  * @c: condition to check for update-side use
 117  *
 118  * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
 119  * critical section will result in an RCU-lockdep splat, unless @c evaluates
 120  * to 1.  The @c argument will normally be a logical expression containing
 121  * lockdep_is_held() calls.
 122  */
 123 #define srcu_dereference_check(p, sp, c) \
 124         __rcu_dereference_check((p), (c) || srcu_read_lock_held(sp), __rcu)
 125
 126 /**
 127  * srcu_dereference - 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  *
 132  * Makes rcu_dereference_check() do the dirty work.  If PROVE_RCU
 133  * is enabled, invoking this outside of an RCU read-side critical
 134  * section will result in an RCU-lockdep splat.
 135  */
 136 #define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0)
 137
 138 /**
 139  * srcu_read_lock - register a new reader for an SRCU-protected structure.
 140  * @sp: srcu_struct in which to register the new reader.
 141  *
 142  * Enter an SRCU read-side critical section.  Note that SRCU read-side
 143  * critical sections may be nested.  However, it is illegal to
 144  * call anything that waits on an SRCU grace period for the same
 145  * srcu_struct, whether directly or indirectly.  Please note that
 146  * one way to indirectly wait on an SRCU grace period is to acquire
 147  * a mutex that is held elsewhere while calling synchronize_srcu() or
 148  * synchronize_srcu_expedited().
 149  *
 150  * Note that srcu_read_lock() and the matching srcu_read_unlock() must
 151  * occur in the same context, for example, it is illegal to invoke
 152  * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
 153  * was invoked in process context.
 154  */
 155 static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
 156 {
 157         int retval;
 158
 159         retval = __srcu_read_lock(sp);
 160         rcu_lock_acquire(&(sp)->dep_map);
 161         return retval;
 162 }
 163
 164 /**
 165  * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
 166  * @sp: srcu_struct in which to unregister the old reader.
 167  * @idx: return value from corresponding srcu_read_lock().
 168  *
 169  * Exit an SRCU read-side critical section.
 170  */
 171 static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
 172         __releases(sp)
 173 {
 174         rcu_lock_release(&(sp)->dep_map);
 175         __srcu_read_unlock(sp, idx);
 176 }
 177
 178 /**
 179  * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
 180  *
 181  * Converts the preceding srcu_read_unlock into a two-way memory barrier.
 182  *
 183  * Call this after srcu_read_unlock, to guarantee that all memory operations
 184  * that occur after smp_mb__after_srcu_read_unlock will appear to happen after
 185  * the preceding srcu_read_unlock.
 186  */
 187 static inline void smp_mb__after_srcu_read_unlock(void)
 188 {
 189         /* __srcu_read_unlock has smp_mb() internally so nothing to do here. */
 190 }
 191
 192 #endif