kernel/rcupdate.c

   1 /*
   2  * 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 IBM Corporation, 2001
  19  *
  20  * Authors: Dipankar Sarma <dipankar@in.ibm.com>
  21  *          Manfred Spraul <manfred@colorfullife.com>
  22  *
  23  * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
  24  * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
  25  * Papers:
  26  * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
  27  * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
  28  *
  29  * For detailed explanation of Read-Copy Update mechanism see -
  30  *              http://lse.sourceforge.net/locking/rcupdate.html
  31  *
  32  */
  33 #include <linux/types.h>
  34 #include <linux/kernel.h>
  35 #include <linux/init.h>
  36 #include <linux/spinlock.h>
  37 #include <linux/smp.h>
  38 #include <linux/interrupt.h>
  39 #include <linux/sched.h>
  40 #include <asm/atomic.h>
  41 #include <linux/bitops.h>
  42 #include <linux/percpu.h>
  43 #include <linux/notifier.h>
  44 #include <linux/cpu.h>
  45 #include <linux/mutex.h>
  46 #include <linux/module.h>
  47 #include <linux/hardirq.h>
  48
  49 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  50 static struct lock_class_key rcu_lock_key;
  51 struct lockdep_map rcu_lock_map =
  52         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
  53 EXPORT_SYMBOL_GPL(rcu_lock_map);
  54
  55 static struct lock_class_key rcu_bh_lock_key;
  56 struct lockdep_map rcu_bh_lock_map =
  57         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
  58 EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
  59
  60 static struct lock_class_key rcu_sched_lock_key;
  61 struct lockdep_map rcu_sched_lock_map =
  62         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
  63 EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
  64 #endif
  65
  66 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  67
  68 int debug_lockdep_rcu_enabled(void)
  69 {
  70         return rcu_scheduler_active && debug_locks &&
  71                current->lockdep_recursion == 0;
  72 }
  73 EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
  74
  75 /**
  76  * rcu_read_lock_bh_held - might we be in RCU-bh read-side critical section?
  77  *
  78  * Check for bottom half being disabled, which covers both the
  79  * CONFIG_PROVE_RCU and not cases.  Note that if someone uses
  80  * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
  81  * will show the situation.
  82  *
  83  * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
  84  */
  85 int rcu_read_lock_bh_held(void)
  86 {
  87         if (!debug_lockdep_rcu_enabled())
  88                 return 1;
  89         return in_softirq();
  90 }
  91 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
  92
  93 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  94
  95 /*
  96  * Awaken the corresponding synchronize_rcu() instance now that a
  97  * grace period has elapsed.
  98  */
  99 void wakeme_after_rcu(struct rcu_head  *head)
 100 {
 101         struct rcu_synchronize *rcu;
 102
 103         rcu = container_of(head, struct rcu_synchronize, head);
 104         complete(&rcu->completion);
 105 }
 106
 107 #ifdef CONFIG_PROVE_RCU
 108 /*
 109  * wrapper function to avoid #include problems.
 110  */
 111 int rcu_my_thread_group_empty(void)
 112 {
 113         return thread_group_empty(current);
 114 }
 115 EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
 116 #endif /* #ifdef CONFIG_PROVE_RCU */