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
  36 struct srcu_struct_array {
  37         unsigned long c[2];
  38         unsigned long seq[2];
  39 };
  40
  41 struct rcu_batch {
  42         struct rcu_head *head, **tail;
  43 };
  44
  45 #define RCU_BATCH_INIT(name) { NULL, &(name.head) }
  46
  47 struct srcu_struct {
  48         unsigned long 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
  67 int __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
  80 int 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
  85 void 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 initialize a srcu struct at build time.
 103  * Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it.
 104  *
 105  * Note that although DEFINE_STATIC_SRCU() hides the name from other
 106  * files, the per-CPU variable rules nevertheless require that the
 107  * chosen name be globally unique.  These rules also prohibit use of
 108  * DEFINE_STATIC_SRCU() within a function.  If these rules are too
 109  * restrictive, declare the srcu_struct manually.  For example, in
 110  * each file:
 111  *
 112  *      static struct srcu_struct my_srcu;
 113  *
 114  * Then, before the first use of each my_srcu, manually initialize it:
 115  *
 116  *      init_srcu_struct(&my_srcu);
 117  *
 118  * See include/linux/percpu-defs.h for the rules on per-CPU variables.
 119  */
 120 #define __DEFINE_SRCU(name, is_static)                                  \
 121         static DEFINE_PER_CPU(struct srcu_struct_array, name##_srcu_array);\
 122         is_static struct srcu_struct name = __SRCU_STRUCT_INIT(name)
 123 #define DEFINE_SRCU(name)               __DEFINE_SRCU(name, /* not static */)
 124 #define DEFINE_STATIC_SRCU(name)        __DEFINE_SRCU(name, static)
 125
 126 /**
 127  * call_srcu() - Queue a callback for invocation after an SRCU grace period
 128  * @sp: srcu_struct in queue the callback
 129  * @head: structure to be used for queueing the SRCU callback.
 130  * @func: function to be invoked after the SRCU grace period
 131  *
 132  * The callback function will be invoked some time after a full SRCU
 133  * grace period elapses, in other words after all pre-existing SRCU
 134  * read-side critical sections have completed.  However, the callback
 135  * function might well execute concurrently with other SRCU read-side
 136  * critical sections that started after call_srcu() was invoked.  SRCU
 137  * read-side critical sections are delimited by srcu_read_lock() and
 138  * srcu_read_unlock(), and may be nested.
 139  *
 140  * The callback will be invoked from process context, but must nevertheless
 141  * be fast and must not block.
 142  */
 143 void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
 144                 void (*func)(struct rcu_head *head));
 145
 146 void cleanup_srcu_struct(struct srcu_struct *sp);
 147 int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
 148 void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
 149 void synchronize_srcu(struct srcu_struct *sp);
 150 void synchronize_srcu_expedited(struct srcu_struct *sp);
 151 unsigned long srcu_batches_completed(struct srcu_struct *sp);
 152 void srcu_barrier(struct srcu_struct *sp);
 153
 154 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 155
 156 /**
 157  * srcu_read_lock_held - might we be in SRCU read-side critical section?
 158  *
 159  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
 160  * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
 161  * this assumes we are in an SRCU read-side critical section unless it can
 162  * prove otherwise.
 163  *
 164  * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
 165  * and while lockdep is disabled.
 166  *
 167  * Note that SRCU is based on its own statemachine and it doesn't
 168  * relies on normal RCU, it can be called from the CPU which
 169  * is in the idle loop from an RCU point of view or offline.
 170  */
 171 static inline int srcu_read_lock_held(struct srcu_struct *sp)
 172 {
 173         if (!debug_lockdep_rcu_enabled())
 174                 return 1;
 175         return lock_is_held(&sp->dep_map);
 176 }
 177
 178 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 179
 180 static inline int srcu_read_lock_held(struct srcu_struct *sp)
 181 {
 182         return 1;
 183 }
 184
 185 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 186
 187 /**
 188  * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
 189  * @p: the pointer to fetch and protect for later dereferencing
 190  * @sp: pointer to the srcu_struct, which is used to check that we
 191  *      really are in an SRCU read-side critical section.
 192  * @c: condition to check for update-side use
 193  *
 194  * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
 195  * critical section will result in an RCU-lockdep splat, unless @c evaluates
 196  * to 1.  The @c argument will normally be a logical expression containing
 197  * lockdep_is_held() calls.
 198  */
 199 #define srcu_dereference_check(p, sp, c) \
 200         __rcu_dereference_check((p), (c) || srcu_read_lock_held(sp), __rcu)
 201
 202 /**
 203  * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
 204  * @p: the pointer to fetch and protect for later dereferencing
 205  * @sp: pointer to the srcu_struct, which is used to check that we
 206  *      really are in an SRCU read-side critical section.
 207  *
 208  * Makes rcu_dereference_check() do the dirty work.  If PROVE_RCU
 209  * is enabled, invoking this outside of an RCU read-side critical
 210  * section will result in an RCU-lockdep splat.
 211  */
 212 #define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0)
 213
 214 /**
 215  * srcu_read_lock - register a new reader for an SRCU-protected structure.
 216  * @sp: srcu_struct in which to register the new reader.
 217  *
 218  * Enter an SRCU read-side critical section.  Note that SRCU read-side
 219  * critical sections may be nested.  However, it is illegal to
 220  * call anything that waits on an SRCU grace period for the same
 221  * srcu_struct, whether directly or indirectly.  Please note that
 222  * one way to indirectly wait on an SRCU grace period is to acquire
 223  * a mutex that is held elsewhere while calling synchronize_srcu() or
 224  * synchronize_srcu_expedited().
 225  *
 226  * Note that srcu_read_lock() and the matching srcu_read_unlock() must
 227  * occur in the same context, for example, it is illegal to invoke
 228  * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
 229  * was invoked in process context.
 230  */
 231 static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
 232 {
 233         int retval;
 234
 235         preempt_disable();
 236         retval = __srcu_read_lock(sp);
 237         preempt_enable();
 238         rcu_lock_acquire(&(sp)->dep_map);
 239         return retval;
 240 }
 241
 242 /**
 243  * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
 244  * @sp: srcu_struct in which to unregister the old reader.
 245  * @idx: return value from corresponding srcu_read_lock().
 246  *
 247  * Exit an SRCU read-side critical section.
 248  */
 249 static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
 250         __releases(sp)
 251 {
 252         rcu_lock_release(&(sp)->dep_map);
 253         __srcu_read_unlock(sp, idx);
 254 }
 255
 256 /**
 257  * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
 258  *
 259  * Converts the preceding srcu_read_unlock into a two-way memory barrier.
 260  *
 261  * Call this after srcu_read_unlock, to guarantee that all memory operations
 262  * that occur after smp_mb__after_srcu_read_unlock will appear to happen after
 263  * the preceding srcu_read_unlock.
 264  */
 265 static inline void smp_mb__after_srcu_read_unlock(void)
 266 {
 267         /* __srcu_read_unlock has smp_mb() internally so nothing to do here. */
 268 }
 269
 270 #endif