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, write to the Free Software
  16  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  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 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)                                               \
 106         static DEFINE_PER_CPU(struct srcu_struct_array, name##_srcu_array);\
 107         struct srcu_struct name = __SRCU_STRUCT_INIT(name);
 108
 109 #define DEFINE_STATIC_SRCU(name)                                        \
 110         static DEFINE_PER_CPU(struct srcu_struct_array, name##_srcu_array);\
 111         static struct srcu_struct name = __SRCU_STRUCT_INIT(name);
 112
 113 /**
 114  * call_srcu() - Queue a callback for invocation after an SRCU grace period
 115  * @sp: srcu_struct in queue the callback
 116  * @head: structure to be used for queueing the SRCU callback.
 117  * @func: function to be invoked after the SRCU grace period
 118  *
 119  * The callback function will be invoked some time after a full SRCU
 120  * grace period elapses, in other words after all pre-existing SRCU
 121  * read-side critical sections have completed.  However, the callback
 122  * function might well execute concurrently with other SRCU read-side
 123  * critical sections that started after call_srcu() was invoked.  SRCU
 124  * read-side critical sections are delimited by srcu_read_lock() and
 125  * srcu_read_unlock(), and may be nested.
 126  *
 127  * The callback will be invoked from process context, but must nevertheless
 128  * be fast and must not block.
 129  */
 130 void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
 131                 void (*func)(struct rcu_head *head));
 132
 133 void cleanup_srcu_struct(struct srcu_struct *sp);
 134 int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
 135 void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
 136 void synchronize_srcu(struct srcu_struct *sp);
 137 void synchronize_srcu_expedited(struct srcu_struct *sp);
 138 long srcu_batches_completed(struct srcu_struct *sp);
 139 void srcu_barrier(struct srcu_struct *sp);
 140
 141 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 142
 143 /**
 144  * srcu_read_lock_held - might we be in SRCU read-side critical section?
 145  *
 146  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
 147  * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
 148  * this assumes we are in an SRCU read-side critical section unless it can
 149  * prove otherwise.
 150  *
 151  * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
 152  * and while lockdep is disabled.
 153  *
 154  * Note that SRCU is based on its own statemachine and it doesn't
 155  * relies on normal RCU, it can be called from the CPU which
 156  * is in the idle loop from an RCU point of view or offline.
 157  */
 158 static inline int srcu_read_lock_held(struct srcu_struct *sp)
 159 {
 160         if (!debug_lockdep_rcu_enabled())
 161                 return 1;
 162         return lock_is_held(&sp->dep_map);
 163 }
 164
 165 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 166
 167 static inline int srcu_read_lock_held(struct srcu_struct *sp)
 168 {
 169         return 1;
 170 }
 171
 172 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 173
 174 /**
 175  * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
 176  * @p: the pointer to fetch and protect for later dereferencing
 177  * @sp: pointer to the srcu_struct, which is used to check that we
 178  *      really are in an SRCU read-side critical section.
 179  * @c: condition to check for update-side use
 180  *
 181  * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
 182  * critical section will result in an RCU-lockdep splat, unless @c evaluates
 183  * to 1.  The @c argument will normally be a logical expression containing
 184  * lockdep_is_held() calls.
 185  */
 186 #define srcu_dereference_check(p, sp, c) \
 187         __rcu_dereference_check((p), srcu_read_lock_held(sp) || (c), __rcu)
 188
 189 /**
 190  * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
 191  * @p: the pointer to fetch and protect for later dereferencing
 192  * @sp: pointer to the srcu_struct, which is used to check that we
 193  *      really are in an SRCU read-side critical section.
 194  *
 195  * Makes rcu_dereference_check() do the dirty work.  If PROVE_RCU
 196  * is enabled, invoking this outside of an RCU read-side critical
 197  * section will result in an RCU-lockdep splat.
 198  */
 199 #define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0)
 200
 201 /**
 202  * srcu_read_lock - register a new reader for an SRCU-protected structure.
 203  * @sp: srcu_struct in which to register the new reader.
 204  *
 205  * Enter an SRCU read-side critical section.  Note that SRCU read-side
 206  * critical sections may be nested.  However, it is illegal to
 207  * call anything that waits on an SRCU grace period for the same
 208  * srcu_struct, whether directly or indirectly.  Please note that
 209  * one way to indirectly wait on an SRCU grace period is to acquire
 210  * a mutex that is held elsewhere while calling synchronize_srcu() or
 211  * synchronize_srcu_expedited().
 212  *
 213  * Note that srcu_read_lock() and the matching srcu_read_unlock() must
 214  * occur in the same context, for example, it is illegal to invoke
 215  * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
 216  * was invoked in process context.
 217  */
 218 static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
 219 {
 220         int retval = __srcu_read_lock(sp);
 221
 222         rcu_lock_acquire(&(sp)->dep_map);
 223         return retval;
 224 }
 225
 226 /**
 227  * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
 228  * @sp: srcu_struct in which to unregister the old reader.
 229  * @idx: return value from corresponding srcu_read_lock().
 230  *
 231  * Exit an SRCU read-side critical section.
 232  */
 233 static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
 234         __releases(sp)
 235 {
 236         rcu_lock_release(&(sp)->dep_map);
 237         __srcu_read_unlock(sp, idx);
 238 }
 239
 240 /**
 241  * srcu_read_lock_raw - register a new reader for an SRCU-protected structure.
 242  * @sp: srcu_struct in which to register the new reader.
 243  *
 244  * Enter an SRCU read-side critical section.  Similar to srcu_read_lock(),
 245  * but avoids the RCU-lockdep checking.  This means that it is legal to
 246  * use srcu_read_lock_raw() in one context, for example, in an exception
 247  * handler, and then have the matching srcu_read_unlock_raw() in another
 248  * context, for example in the task that took the exception.
 249  *
 250  * However, the entire SRCU read-side critical section must reside within a
 251  * single task.  For example, beware of using srcu_read_lock_raw() in
 252  * a device interrupt handler and srcu_read_unlock() in the interrupted
 253  * task:  This will not work if interrupts are threaded.
 254  */
 255 static inline int srcu_read_lock_raw(struct srcu_struct *sp)
 256 {
 257         unsigned long flags;
 258         int ret;
 259
 260         local_irq_save(flags);
 261         ret =  __srcu_read_lock(sp);
 262         local_irq_restore(flags);
 263         return ret;
 264 }
 265
 266 /**
 267  * srcu_read_unlock_raw - unregister reader from an SRCU-protected structure.
 268  * @sp: srcu_struct in which to unregister the old reader.
 269  * @idx: return value from corresponding srcu_read_lock_raw().
 270  *
 271  * Exit an SRCU read-side critical section without lockdep-RCU checking.
 272  * See srcu_read_lock_raw() for more details.
 273  */
 274 static inline void srcu_read_unlock_raw(struct srcu_struct *sp, int idx)
 275 {
 276         unsigned long flags;
 277
 278         local_irq_save(flags);
 279         __srcu_read_unlock(sp, idx);
 280         local_irq_restore(flags);
 281 }
 282
 283 #endif