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/kernel_stat.h>
  48 #include <linux/hardirq.h>
  49
  50 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  51 static struct lock_class_key rcu_lock_key;
  52 struct lockdep_map rcu_lock_map =
  53         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
  54 EXPORT_SYMBOL_GPL(rcu_lock_map);
  55
  56 static struct lock_class_key rcu_bh_lock_key;
  57 struct lockdep_map rcu_bh_lock_map =
  58         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
  59 EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
  60
  61 static struct lock_class_key rcu_sched_lock_key;
  62 struct lockdep_map rcu_sched_lock_map =
  63         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
  64 EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
  65 #endif
  66
  67 int rcu_scheduler_active __read_mostly;
  68 EXPORT_SYMBOL_GPL(rcu_scheduler_active);
  69
  70 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  71
  72 int debug_lockdep_rcu_enabled(void)
  73 {
  74         return rcu_scheduler_active && debug_locks &&
  75                current->lockdep_recursion == 0;
  76 }
  77 EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
  78
  79 /**
  80  * rcu_read_lock_bh_held - might we be in RCU-bh read-side critical section?
  81  *
  82  * Check for bottom half being disabled, which covers both the
  83  * CONFIG_PROVE_RCU and not cases.  Note that if someone uses
  84  * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
  85  * will show the situation.
  86  *
  87  * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
  88  */
  89 int rcu_read_lock_bh_held(void)
  90 {
  91         if (!debug_lockdep_rcu_enabled())
  92                 return 1;
  93         return in_softirq();
  94 }
  95 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
  96
  97 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  98
  99 /*
 100  * This function is invoked towards the end of the scheduler's initialization
 101  * process.  Before this is called, the idle task might contain
 102  * RCU read-side critical sections (during which time, this idle
 103  * task is booting the system).  After this function is called, the
 104  * idle tasks are prohibited from containing RCU read-side critical
 105  * sections.
 106  */
 107 void rcu_scheduler_starting(void)
 108 {
 109         WARN_ON(num_online_cpus() != 1);
 110         WARN_ON(nr_context_switches() > 0);
 111         rcu_scheduler_active = 1;
 112 }
 113
 114 /*
 115  * Awaken the corresponding synchronize_rcu() instance now that a
 116  * grace period has elapsed.
 117  */
 118 void wakeme_after_rcu(struct rcu_head  *head)
 119 {
 120         struct rcu_synchronize *rcu;
 121
 122         rcu = container_of(head, struct rcu_synchronize, head);
 123         complete(&rcu->completion);
 124 }