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