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