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  *
  20  * Author: Paul McKenney <paulmck@us.ibm.com>
  21  *
  22  * For detailed explanation of Read-Copy Update mechanism see -
  23  *              Documentation/RCU/ *.txt
  24  *
  25  */
  26
  27 #ifndef _LINUX_SRCU_H
  28 #define _LINUX_SRCU_H
  29
  30 #include <linux/mutex.h>
  31 #include <linux/rcupdate.h>
  32 #include <linux/workqueue.h>
  33
  34 struct srcu_struct_array {
  35         unsigned long c[2];
  36         unsigned long seq[2];
  37 };
  38
  39 struct rcu_batch {
  40         struct rcu_head *head, **tail;
  41 };
  42
  43 struct srcu_struct {
  44         unsigned completed;
  45         struct srcu_struct_array __percpu *per_cpu_ref;
  46         spinlock_t queue_lock; /* protect ->batch_queue, ->running */
  47         bool running;
  48         /* callbacks just queued */
  49         struct rcu_batch batch_queue;
  50         /* callbacks try to do the first check_zero */
  51         struct rcu_batch batch_check0;
  52         /* callbacks done with the first check_zero and the flip */
  53         struct rcu_batch batch_check1;
  54         struct rcu_batch batch_done;
  55         struct delayed_work work;
  56 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  57         struct lockdep_map dep_map;
  58 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  59 };
  60
  61 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  62
  63 int __init_srcu_struct(struct srcu_struct *sp, const char *name,
  64                        struct lock_class_key *key);
  65
  66 #define init_srcu_struct(sp) \
  67 ({ \
  68         static struct lock_class_key __srcu_key; \
  69         \
  70         __init_srcu_struct((sp), #sp, &__srcu_key); \
  71 })
  72
  73 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  74
  75 int init_srcu_struct(struct srcu_struct *sp);
  76
  77 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  78
  79 /**
  80  * call_srcu() - Queue a callback for invocation after an SRCU grace period
  81  * @sp: srcu_struct in queue the callback
  82  * @head: structure to be used for queueing the SRCU callback.
  83  * @func: function to be invoked after the SRCU grace period
  84  *
  85  * The callback function will be invoked some time after a full SRCU
  86  * grace period elapses, in other words after all pre-existing SRCU
  87  * read-side critical sections have completed.  However, the callback
  88  * function might well execute concurrently with other SRCU read-side
  89  * critical sections that started after call_srcu() was invoked.  SRCU
  90  * read-side critical sections are delimited by srcu_read_lock() and
  91  * srcu_read_unlock(), and may be nested.
  92  *
  93  * The callback will be invoked from process context, but must nevertheless
  94  * be fast and must not block.
  95  */
  96 void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
  97                 void (*func)(struct rcu_head *head));
  98
  99 void cleanup_srcu_struct(struct srcu_struct *sp);
 100 int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
 101 void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
 102 void synchronize_srcu(struct srcu_struct *sp);
 103 void synchronize_srcu_expedited(struct srcu_struct *sp);
 104 long srcu_batches_completed(struct srcu_struct *sp);
 105 void srcu_barrier(struct srcu_struct *sp);
 106
 107 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 108
 109 /**
 110  * srcu_read_lock_held - might we be in SRCU read-side critical section?
 111  *
 112  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
 113  * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
 114  * this assumes we are in an SRCU read-side critical section unless it can
 115  * prove otherwise.
 116  *
 117  * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
 118  * and while lockdep is disabled.
 119  *
 120  * Note that if the CPU is in the idle loop from an RCU point of view
 121  * (ie: that we are in the section between rcu_idle_enter() and
 122  * rcu_idle_exit()) then srcu_read_lock_held() returns false even if
 123  * the CPU did an srcu_read_lock().  The reason for this is that RCU
 124  * ignores CPUs that are in such a section, considering these as in
 125  * extended quiescent state, so such a CPU is effectively never in an
 126  * RCU read-side critical section regardless of what RCU primitives it
 127  * invokes.  This state of affairs is required --- we need to keep an
 128  * RCU-free window in idle where the CPU may possibly enter into low
 129  * power mode. This way we can notice an extended quiescent state to
 130  * other CPUs that started a grace period. Otherwise we would delay any
 131  * grace period as long as we run in the idle task.
 132  *
 133  * Similarly, we avoid claiming an SRCU read lock held if the current
 134  * CPU is offline.
 135  */
 136 static inline int srcu_read_lock_held(struct srcu_struct *sp)
 137 {
 138         if (!debug_lockdep_rcu_enabled())
 139                 return 1;
 140         if (rcu_is_cpu_idle())
 141                 return 0;
 142         if (!rcu_lockdep_current_cpu_online())
 143                 return 0;
 144         return lock_is_held(&sp->dep_map);
 145 }
 146
 147 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 148
 149 static inline int srcu_read_lock_held(struct srcu_struct *sp)
 150 {
 151         return 1;
 152 }
 153
 154 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 155
 156 /**
 157  * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
 158  * @p: the pointer to fetch and protect for later dereferencing
 159  * @sp: pointer to the srcu_struct, which is used to check that we
 160  *      really are in an SRCU read-side critical section.
 161  * @c: condition to check for update-side use
 162  *
 163  * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
 164  * critical section will result in an RCU-lockdep splat, unless @c evaluates
 165  * to 1.  The @c argument will normally be a logical expression containing
 166  * lockdep_is_held() calls.
 167  */
 168 #define srcu_dereference_check(p, sp, c) \
 169         __rcu_dereference_check((p), srcu_read_lock_held(sp) || (c), __rcu)
 170
 171 /**
 172  * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
 173  * @p: the pointer to fetch and protect for later dereferencing
 174  * @sp: pointer to the srcu_struct, which is used to check that we
 175  *      really are in an SRCU read-side critical section.
 176  *
 177  * Makes rcu_dereference_check() do the dirty work.  If PROVE_RCU
 178  * is enabled, invoking this outside of an RCU read-side critical
 179  * section will result in an RCU-lockdep splat.
 180  */
 181 #define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0)
 182
 183 /**
 184  * srcu_read_lock - register a new reader for an SRCU-protected structure.
 185  * @sp: srcu_struct in which to register the new reader.
 186  *
 187  * Enter an SRCU read-side critical section.  Note that SRCU read-side
 188  * critical sections may be nested.  However, it is illegal to
 189  * call anything that waits on an SRCU grace period for the same
 190  * srcu_struct, whether directly or indirectly.  Please note that
 191  * one way to indirectly wait on an SRCU grace period is to acquire
 192  * a mutex that is held elsewhere while calling synchronize_srcu() or
 193  * synchronize_srcu_expedited().
 194  *
 195  * Note that srcu_read_lock() and the matching srcu_read_unlock() must
 196  * occur in the same context, for example, it is illegal to invoke
 197  * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
 198  * was invoked in process context.
 199  */
 200 static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
 201 {
 202         int retval = __srcu_read_lock(sp);
 203
 204         rcu_lock_acquire(&(sp)->dep_map);
 205         rcu_lockdep_assert(!rcu_is_cpu_idle(),
 206                            "srcu_read_lock() used illegally while idle");
 207         return retval;
 208 }
 209
 210 /**
 211  * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
 212  * @sp: srcu_struct in which to unregister the old reader.
 213  * @idx: return value from corresponding srcu_read_lock().
 214  *
 215  * Exit an SRCU read-side critical section.
 216  */
 217 static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
 218         __releases(sp)
 219 {
 220         rcu_lockdep_assert(!rcu_is_cpu_idle(),
 221                            "srcu_read_unlock() used illegally while idle");
 222         rcu_lock_release(&(sp)->dep_map);
 223         __srcu_read_unlock(sp, idx);
 224 }
 225
 226 /**
 227  * srcu_read_lock_raw - register a new reader for an SRCU-protected structure.
 228  * @sp: srcu_struct in which to register the new reader.
 229  *
 230  * Enter an SRCU read-side critical section.  Similar to srcu_read_lock(),
 231  * but avoids the RCU-lockdep checking.  This means that it is legal to
 232  * use srcu_read_lock_raw() in one context, for example, in an exception
 233  * handler, and then have the matching srcu_read_unlock_raw() in another
 234  * context, for example in the task that took the exception.
 235  *
 236  * However, the entire SRCU read-side critical section must reside within a
 237  * single task.  For example, beware of using srcu_read_lock_raw() in
 238  * a device interrupt handler and srcu_read_unlock() in the interrupted
 239  * task:  This will not work if interrupts are threaded.
 240  */
 241 static inline int srcu_read_lock_raw(struct srcu_struct *sp)
 242 {
 243         unsigned long flags;
 244         int ret;
 245
 246         local_irq_save(flags);
 247         ret =  __srcu_read_lock(sp);
 248         local_irq_restore(flags);
 249         return ret;
 250 }
 251
 252 /**
 253  * srcu_read_unlock_raw - unregister reader from an SRCU-protected structure.
 254  * @sp: srcu_struct in which to unregister the old reader.
 255  * @idx: return value from corresponding srcu_read_lock_raw().
 256  *
 257  * Exit an SRCU read-side critical section without lockdep-RCU checking.
 258  * See srcu_read_lock_raw() for more details.
 259  */
 260 static inline void srcu_read_unlock_raw(struct srcu_struct *sp, int idx)
 261 {
 262         unsigned long flags;
 263
 264         local_irq_save(flags);
 265         __srcu_read_unlock(sp, idx);
 266         local_irq_restore(flags);
 267 }
 268
 269 #endif