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