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.  This is useful for debug checks in functions
  82  * that require that they be called within an RCU read-side critical
  83  * section.
  84  *
  85  * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
  86  */
  87 int rcu_read_lock_bh_held(void)
  88 {
  89         if (!debug_lockdep_rcu_enabled())
  90                 return 1;
  91         return in_softirq() || irqs_disabled();
  92 }
  93 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
  94
  95 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  96
  97 /*
  98  * Awaken the corresponding synchronize_rcu() instance now that a
  99  * grace period has elapsed.
 100  */
 101 void wakeme_after_rcu(struct rcu_head  *head)
 102 {
 103         struct rcu_synchronize *rcu;
 104
 105         rcu = container_of(head, struct rcu_synchronize, head);
 106         complete(&rcu->completion);
 107 }
 108
 109 #ifdef CONFIG_PROVE_RCU
 110 /*
 111  * wrapper function to avoid #include problems.
 112  */
 113 int rcu_my_thread_group_empty(void)
 114 {
 115         return thread_group_empty(current);
 116 }
 117 EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
 118 #endif /* #ifdef CONFIG_PROVE_RCU */
 119
 120 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
 121 static inline void debug_init_rcu_head(struct rcu_head *head)
 122 {
 123         debug_object_init(head, &rcuhead_debug_descr);
 124 }
 125
 126 static inline void debug_rcu_head_free(struct rcu_head *head)
 127 {
 128         debug_object_free(head, &rcuhead_debug_descr);
 129 }
 130
 131 /*
 132  * fixup_init is called when:
 133  * - an active object is initialized
 134  */
 135 static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
 136 {
 137         struct rcu_head *head = addr;
 138
 139         switch (state) {
 140         case ODEBUG_STATE_ACTIVE:
 141                 /*
 142                  * Ensure that queued callbacks are all executed.
 143                  * If we detect that we are nested in a RCU read-side critical
 144                  * section, we should simply fail, otherwise we would deadlock.
 145                  * In !PREEMPT configurations, there is no way to tell if we are
 146                  * in a RCU read-side critical section or not, so we never
 147                  * attempt any fixup and just print a warning.
 148                  */
 149 #ifndef CONFIG_PREEMPT
 150                 WARN_ON_ONCE(1);
 151                 return 0;
 152 #endif
 153                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 154                     irqs_disabled()) {
 155                         WARN_ON_ONCE(1);
 156                         return 0;
 157                 }
 158                 rcu_barrier();
 159                 rcu_barrier_sched();
 160                 rcu_barrier_bh();
 161                 debug_object_init(head, &rcuhead_debug_descr);
 162                 return 1;
 163         default:
 164                 return 0;
 165         }
 166 }
 167
 168 /*
 169  * fixup_activate is called when:
 170  * - an active object is activated
 171  * - an unknown object is activated (might be a statically initialized object)
 172  * Activation is performed internally by call_rcu().
 173  */
 174 static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
 175 {
 176         struct rcu_head *head = addr;
 177
 178         switch (state) {
 179
 180         case ODEBUG_STATE_NOTAVAILABLE:
 181                 /*
 182                  * This is not really a fixup. We just make sure that it is
 183                  * tracked in the object tracker.
 184                  */
 185                 debug_object_init(head, &rcuhead_debug_descr);
 186                 debug_object_activate(head, &rcuhead_debug_descr);
 187                 return 0;
 188
 189         case ODEBUG_STATE_ACTIVE:
 190                 /*
 191                  * Ensure that queued callbacks are all executed.
 192                  * If we detect that we are nested in a RCU read-side critical
 193                  * section, we should simply fail, otherwise we would deadlock.
 194                  * In !PREEMPT configurations, there is no way to tell if we are
 195                  * in a RCU read-side critical section or not, so we never
 196                  * attempt any fixup and just print a warning.
 197                  */
 198 #ifndef CONFIG_PREEMPT
 199                 WARN_ON_ONCE(1);
 200                 return 0;
 201 #endif
 202                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 203                     irqs_disabled()) {
 204                         WARN_ON_ONCE(1);
 205                         return 0;
 206                 }
 207                 rcu_barrier();
 208                 rcu_barrier_sched();
 209                 rcu_barrier_bh();
 210                 debug_object_activate(head, &rcuhead_debug_descr);
 211                 return 1;
 212         default:
 213                 return 0;
 214         }
 215 }
 216
 217 /*
 218  * fixup_free is called when:
 219  * - an active object is freed
 220  */
 221 static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
 222 {
 223         struct rcu_head *head = addr;
 224
 225         switch (state) {
 226         case ODEBUG_STATE_ACTIVE:
 227                 /*
 228                  * Ensure that queued callbacks are all executed.
 229                  * If we detect that we are nested in a RCU read-side critical
 230                  * section, we should simply fail, otherwise we would deadlock.
 231                  * In !PREEMPT configurations, there is no way to tell if we are
 232                  * in a RCU read-side critical section or not, so we never
 233                  * attempt any fixup and just print a warning.
 234                  */
 235 #ifndef CONFIG_PREEMPT
 236                 WARN_ON_ONCE(1);
 237                 return 0;
 238 #endif
 239                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 240                     irqs_disabled()) {
 241                         WARN_ON_ONCE(1);
 242                         return 0;
 243                 }
 244                 rcu_barrier();
 245                 rcu_barrier_sched();
 246                 rcu_barrier_bh();
 247                 debug_object_free(head, &rcuhead_debug_descr);
 248                 return 1;
 249         default:
 250                 return 0;
 251         }
 252 }
 253
 254 /**
 255  * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
 256  * @head: pointer to rcu_head structure to be initialized
 257  *
 258  * This function informs debugobjects of a new rcu_head structure that
 259  * has been allocated as an auto variable on the stack.  This function
 260  * is not required for rcu_head structures that are statically defined or
 261  * that are dynamically allocated on the heap.  This function has no
 262  * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 263  */
 264 void init_rcu_head_on_stack(struct rcu_head *head)
 265 {
 266         debug_object_init_on_stack(head, &rcuhead_debug_descr);
 267 }
 268 EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
 269
 270 /**
 271  * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
 272  * @head: pointer to rcu_head structure to be initialized
 273  *
 274  * This function informs debugobjects that an on-stack rcu_head structure
 275  * is about to go out of scope.  As with init_rcu_head_on_stack(), this
 276  * function is not required for rcu_head structures that are statically
 277  * defined or that are dynamically allocated on the heap.  Also as with
 278  * init_rcu_head_on_stack(), this function has no effect for
 279  * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 280  */
 281 void destroy_rcu_head_on_stack(struct rcu_head *head)
 282 {
 283         debug_object_free(head, &rcuhead_debug_descr);
 284 }
 285 EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
 286
 287 struct debug_obj_descr rcuhead_debug_descr = {
 288         .name = "rcu_head",
 289         .fixup_init = rcuhead_fixup_init,
 290         .fixup_activate = rcuhead_fixup_activate,
 291         .fixup_free = rcuhead_fixup_free,
 292 };
 293 EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
 294 #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */