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 */
 117
 118 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
 119 static inline void debug_init_rcu_head(struct rcu_head *head)
 120 {
 121         debug_object_init(head, &rcuhead_debug_descr);
 122 }
 123
 124 static inline void debug_rcu_head_free(struct rcu_head *head)
 125 {
 126         debug_object_free(head, &rcuhead_debug_descr);
 127 }
 128
 129 /*
 130  * fixup_init is called when:
 131  * - an active object is initialized
 132  */
 133 static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
 134 {
 135         struct rcu_head *head = addr;
 136
 137         switch (state) {
 138         case ODEBUG_STATE_ACTIVE:
 139                 /*
 140                  * Ensure that queued callbacks are all executed.
 141                  * If we detect that we are nested in a RCU read-side critical
 142                  * section, we should simply fail, otherwise we would deadlock.
 143                  */
 144                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 145                     irqs_disabled()) {
 146                         WARN_ON(1);
 147                         return 0;
 148                 }
 149                 rcu_barrier();
 150                 rcu_barrier_sched();
 151                 rcu_barrier_bh();
 152                 debug_object_init(head, &rcuhead_debug_descr);
 153                 return 1;
 154         default:
 155                 return 0;
 156         }
 157 }
 158
 159 /*
 160  * fixup_activate is called when:
 161  * - an active object is activated
 162  * - an unknown object is activated (might be a statically initialized object)
 163  * Activation is performed internally by call_rcu().
 164  */
 165 static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
 166 {
 167         struct rcu_head *head = addr;
 168
 169         switch (state) {
 170
 171         case ODEBUG_STATE_NOTAVAILABLE:
 172                 /*
 173                  * This is not really a fixup. We just make sure that it is
 174                  * tracked in the object tracker.
 175                  */
 176                 debug_object_init(head, &rcuhead_debug_descr);
 177                 debug_object_activate(head, &rcuhead_debug_descr);
 178                 return 0;
 179
 180         case ODEBUG_STATE_ACTIVE:
 181                 /*
 182                  * Ensure that queued callbacks are all executed.
 183                  * If we detect that we are nested in a RCU read-side critical
 184                  * section, we should simply fail, otherwise we would deadlock.
 185                  */
 186                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 187                     irqs_disabled()) {
 188                         WARN_ON(1);
 189                         return 0;
 190                 }
 191                 rcu_barrier();
 192                 rcu_barrier_sched();
 193                 rcu_barrier_bh();
 194                 debug_object_activate(head, &rcuhead_debug_descr);
 195                 return 1;
 196         default:
 197                 return 0;
 198         }
 199 }
 200
 201 /*
 202  * fixup_free is called when:
 203  * - an active object is freed
 204  */
 205 static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
 206 {
 207         struct rcu_head *head = addr;
 208
 209         switch (state) {
 210         case ODEBUG_STATE_ACTIVE:
 211                 /*
 212                  * Ensure that queued callbacks are all executed.
 213                  * If we detect that we are nested in a RCU read-side critical
 214                  * section, we should simply fail, otherwise we would deadlock.
 215                  */
 216 #ifndef CONFIG_PREEMPT
 217                 WARN_ON(1);
 218                 return 0;
 219 #else
 220                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 221                     irqs_disabled()) {
 222                         WARN_ON(1);
 223                         return 0;
 224                 }
 225                 rcu_barrier();
 226                 rcu_barrier_sched();
 227                 rcu_barrier_bh();
 228                 debug_object_free(head, &rcuhead_debug_descr);
 229                 return 1;
 230 #endif
 231         default:
 232                 return 0;
 233         }
 234 }
 235
 236 /**
 237  * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
 238  * @head: pointer to rcu_head structure to be initialized
 239  *
 240  * This function informs debugobjects of a new rcu_head structure that
 241  * has been allocated as an auto variable on the stack.  This function
 242  * is not required for rcu_head structures that are statically defined or
 243  * that are dynamically allocated on the heap.  This function has no
 244  * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 245  */
 246 void init_rcu_head_on_stack(struct rcu_head *head)
 247 {
 248         debug_object_init_on_stack(head, &rcuhead_debug_descr);
 249 }
 250 EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
 251
 252 /**
 253  * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
 254  * @head: pointer to rcu_head structure to be initialized
 255  *
 256  * This function informs debugobjects that an on-stack rcu_head structure
 257  * is about to go out of scope.  As with init_rcu_head_on_stack(), this
 258  * function is not required for rcu_head structures that are statically
 259  * defined or that are dynamically allocated on the heap.  Also as with
 260  * init_rcu_head_on_stack(), this function has no effect for
 261  * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 262  */
 263 void destroy_rcu_head_on_stack(struct rcu_head *head)
 264 {
 265         debug_object_free(head, &rcuhead_debug_descr);
 266 }
 267 EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
 268
 269 struct debug_obj_descr rcuhead_debug_descr = {
 270         .name = "rcu_head",
 271         .fixup_init = rcuhead_fixup_init,
 272         .fixup_activate = rcuhead_fixup_activate,
 273         .fixup_free = rcuhead_fixup_free,
 274 };
 275 EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
 276 #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */