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, bool quiesced);
  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 /**
  78  * cleanup_srcu_struct - deconstruct a sleep-RCU structure
  79  * @sp: structure to clean up.
  80  *
  81  * Must invoke this after you are finished using a given srcu_struct that
  82  * was initialized via init_srcu_struct(), else you leak memory.
  83  */
  84 static inline void cleanup_srcu_struct(struct srcu_struct *sp)
  85 {
  86         _cleanup_srcu_struct(sp, false);
  87 }
  88
  89 /**
  90  * cleanup_srcu_struct_quiesced - deconstruct a quiesced sleep-RCU structure
  91  * @sp: structure to clean up.
  92  *
  93  * Must invoke this after you are finished using a given srcu_struct that
  94  * was initialized via init_srcu_struct(), else you leak memory.  Also,
  95  * all grace-period processing must have completed.
  96  *
  97  * "Completed" means that the last synchronize_srcu() and
  98  * synchronize_srcu_expedited() calls must have returned before the call
  99  * to cleanup_srcu_struct_quiesced().  It also means that the callback
 100  * from the last call_srcu() must have been invoked before the call to
 101  * cleanup_srcu_struct_quiesced(), but you can use srcu_barrier() to help
 102  * with this last.  Violating these rules will get you a WARN_ON() splat
 103  * (with high probability, anyway), and will also cause the srcu_struct
 104  * to be leaked.
 105  */
 106 static inline void cleanup_srcu_struct_quiesced(struct srcu_struct *sp)
 107 {
 108         _cleanup_srcu_struct(sp, true);
 109 }
 110
 111 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 112
 113 /**
 114  * srcu_read_lock_held - might we be in SRCU read-side critical section?
 115  * @sp: The srcu_struct structure to check
 116  *
 117  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
 118  * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
 119  * this assumes we are in an SRCU read-side critical section unless it can
 120  * prove otherwise.
 121  *
 122  * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
 123  * and while lockdep is disabled.
 124  *
 125  * Note that SRCU is based on its own statemachine and it doesn't
 126  * relies on normal RCU, it can be called from the CPU which
 127  * is in the idle loop from an RCU point of view or offline.
 128  */
 129 static inline int srcu_read_lock_held(const struct srcu_struct *sp)
 130 {
 131         if (!debug_lockdep_rcu_enabled())
 132                 return 1;
 133         return lock_is_held(&sp->dep_map);
 134 }
 135
 136 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 137
 138 static inline int srcu_read_lock_held(const struct srcu_struct *sp)
 139 {
 140         return 1;
 141 }
 142
 143 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 144
 145 /**
 146  * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
 147  * @p: the pointer to fetch and protect for later dereferencing
 148  * @sp: pointer to the srcu_struct, which is used to check that we
 149  *      really are in an SRCU read-side critical section.
 150  * @c: condition to check for update-side use
 151  *
 152  * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
 153  * critical section will result in an RCU-lockdep splat, unless @c evaluates
 154  * to 1.  The @c argument will normally be a logical expression containing
 155  * lockdep_is_held() calls.
 156  */
 157 #define srcu_dereference_check(p, sp, c) \
 158         __rcu_dereference_check((p), (c) || srcu_read_lock_held(sp), __rcu)
 159
 160 /**
 161  * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
 162  * @p: the pointer to fetch and protect for later dereferencing
 163  * @sp: pointer to the srcu_struct, which is used to check that we
 164  *      really are in an SRCU read-side critical section.
 165  *
 166  * Makes rcu_dereference_check() do the dirty work.  If PROVE_RCU
 167  * is enabled, invoking this outside of an RCU read-side critical
 168  * section will result in an RCU-lockdep splat.
 169  */
 170 #define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0)
 171
 172 /**
 173  * srcu_dereference_notrace - no tracing and no lockdep calls from here
 174  */
 175 #define srcu_dereference_notrace(p, sp) srcu_dereference_check((p), (sp), 1)
 176
 177 /**
 178  * srcu_read_lock - register a new reader for an SRCU-protected structure.
 179  * @sp: srcu_struct in which to register the new reader.
 180  *
 181  * Enter an SRCU read-side critical section.  Note that SRCU read-side
 182  * critical sections may be nested.  However, it is illegal to
 183  * call anything that waits on an SRCU grace period for the same
 184  * srcu_struct, whether directly or indirectly.  Please note that
 185  * one way to indirectly wait on an SRCU grace period is to acquire
 186  * a mutex that is held elsewhere while calling synchronize_srcu() or
 187  * synchronize_srcu_expedited().
 188  *
 189  * Note that srcu_read_lock() and the matching srcu_read_unlock() must
 190  * occur in the same context, for example, it is illegal to invoke
 191  * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
 192  * was invoked in process context.
 193  */
 194 static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
 195 {
 196         int retval;
 197
 198         retval = __srcu_read_lock(sp);
 199         rcu_lock_acquire(&(sp)->dep_map);
 200         return retval;
 201 }
 202
 203 /* Used by tracing, cannot be traced and cannot invoke lockdep. */
 204 static inline notrace int
 205 srcu_read_lock_notrace(struct srcu_struct *sp) __acquires(sp)
 206 {
 207         int retval;
 208
 209         retval = __srcu_read_lock(sp);
 210         return retval;
 211 }
 212
 213 /**
 214  * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
 215  * @sp: srcu_struct in which to unregister the old reader.
 216  * @idx: return value from corresponding srcu_read_lock().
 217  *
 218  * Exit an SRCU read-side critical section.
 219  */
 220 static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
 221         __releases(sp)
 222 {
 223         rcu_lock_release(&(sp)->dep_map);
 224         __srcu_read_unlock(sp, idx);
 225 }
 226
 227 /* Used by tracing, cannot be traced and cannot call lockdep. */
 228 static inline notrace void
 229 srcu_read_unlock_notrace(struct srcu_struct *sp, int idx) __releases(sp)
 230 {
 231         __srcu_read_unlock(sp, idx);
 232 }
 233
 234 /**
 235  * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
 236  *
 237  * Converts the preceding srcu_read_unlock into a two-way memory barrier.
 238  *
 239  * Call this after srcu_read_unlock, to guarantee that all memory operations
 240  * that occur after smp_mb__after_srcu_read_unlock will appear to happen after
 241  * the preceding srcu_read_unlock.
 242  */
 243 static inline void smp_mb__after_srcu_read_unlock(void)
 244 {
 245         /* __srcu_read_unlock has smp_mb() internally so nothing to do here. */
 246 }
 247
 248 #endif