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 <linux/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 #define CREATE_TRACE_POINTS
  50 #include <trace/events/rcu.h>
  51
  52 #include "rcu.h"
  53
  54 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  55 static struct lock_class_key rcu_lock_key;
  56 struct lockdep_map rcu_lock_map =
  57         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
  58 EXPORT_SYMBOL_GPL(rcu_lock_map);
  59
  60 static struct lock_class_key rcu_bh_lock_key;
  61 struct lockdep_map rcu_bh_lock_map =
  62         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
  63 EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
  64
  65 static struct lock_class_key rcu_sched_lock_key;
  66 struct lockdep_map rcu_sched_lock_map =
  67         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
  68 EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
  69 #endif
  70
  71 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  72
  73 int debug_lockdep_rcu_enabled(void)
  74 {
  75         return rcu_scheduler_active && debug_locks &&
  76                current->lockdep_recursion == 0;
  77 }
  78 EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
  79
  80 /**
  81  * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
  82  *
  83  * Check for bottom half being disabled, which covers both the
  84  * CONFIG_PROVE_RCU and not cases.  Note that if someone uses
  85  * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
  86  * will show the situation.  This is useful for debug checks in functions
  87  * that require that they be called within an RCU read-side critical
  88  * section.
  89  *
  90  * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
  91  */
  92 int rcu_read_lock_bh_held(void)
  93 {
  94         if (!debug_lockdep_rcu_enabled())
  95                 return 1;
  96         return in_softirq() || irqs_disabled();
  97 }
  98 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
  99
 100 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 101
 102 struct rcu_synchronize {
 103         struct rcu_head head;
 104         struct completion completion;
 105 };
 106
 107 /*
 108  * Awaken the corresponding synchronize_rcu() instance now that a
 109  * grace period has elapsed.
 110  */
 111 static void wakeme_after_rcu(struct rcu_head  *head)
 112 {
 113         struct rcu_synchronize *rcu;
 114
 115         rcu = container_of(head, struct rcu_synchronize, head);
 116         complete(&rcu->completion);
 117 }
 118
 119 void wait_rcu_gp(call_rcu_func_t crf)
 120 {
 121         struct rcu_synchronize rcu;
 122
 123         init_rcu_head_on_stack(&rcu.head);
 124         init_completion(&rcu.completion);
 125         /* Will wake me after RCU finished. */
 126         crf(&rcu.head, wakeme_after_rcu);
 127         /* Wait for it. */
 128         wait_for_completion(&rcu.completion);
 129         destroy_rcu_head_on_stack(&rcu.head);
 130 }
 131 EXPORT_SYMBOL_GPL(wait_rcu_gp);
 132
 133 #ifdef CONFIG_PROVE_RCU
 134 /*
 135  * wrapper function to avoid #include problems.
 136  */
 137 int rcu_my_thread_group_empty(void)
 138 {
 139         return thread_group_empty(current);
 140 }
 141 EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
 142 #endif /* #ifdef CONFIG_PROVE_RCU */
 143
 144 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
 145 static inline void debug_init_rcu_head(struct rcu_head *head)
 146 {
 147         debug_object_init(head, &rcuhead_debug_descr);
 148 }
 149
 150 static inline void debug_rcu_head_free(struct rcu_head *head)
 151 {
 152         debug_object_free(head, &rcuhead_debug_descr);
 153 }
 154
 155 /*
 156  * fixup_init is called when:
 157  * - an active object is initialized
 158  */
 159 static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
 160 {
 161         struct rcu_head *head = addr;
 162
 163         switch (state) {
 164         case ODEBUG_STATE_ACTIVE:
 165                 /*
 166                  * Ensure that queued callbacks are all executed.
 167                  * If we detect that we are nested in a RCU read-side critical
 168                  * section, we should simply fail, otherwise we would deadlock.
 169                  * In !PREEMPT configurations, there is no way to tell if we are
 170                  * in a RCU read-side critical section or not, so we never
 171                  * attempt any fixup and just print a warning.
 172                  */
 173 #ifndef CONFIG_PREEMPT
 174                 WARN_ON_ONCE(1);
 175                 return 0;
 176 #endif
 177                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 178                     irqs_disabled()) {
 179                         WARN_ON_ONCE(1);
 180                         return 0;
 181                 }
 182                 rcu_barrier();
 183                 rcu_barrier_sched();
 184                 rcu_barrier_bh();
 185                 debug_object_init(head, &rcuhead_debug_descr);
 186                 return 1;
 187         default:
 188                 return 0;
 189         }
 190 }
 191
 192 /*
 193  * fixup_activate is called when:
 194  * - an active object is activated
 195  * - an unknown object is activated (might be a statically initialized object)
 196  * Activation is performed internally by call_rcu().
 197  */
 198 static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
 199 {
 200         struct rcu_head *head = addr;
 201
 202         switch (state) {
 203
 204         case ODEBUG_STATE_NOTAVAILABLE:
 205                 /*
 206                  * This is not really a fixup. We just make sure that it is
 207                  * tracked in the object tracker.
 208                  */
 209                 debug_object_init(head, &rcuhead_debug_descr);
 210                 debug_object_activate(head, &rcuhead_debug_descr);
 211                 return 0;
 212
 213         case ODEBUG_STATE_ACTIVE:
 214                 /*
 215                  * Ensure that queued callbacks are all executed.
 216                  * If we detect that we are nested in a RCU read-side critical
 217                  * section, we should simply fail, otherwise we would deadlock.
 218                  * In !PREEMPT configurations, there is no way to tell if we are
 219                  * in a RCU read-side critical section or not, so we never
 220                  * attempt any fixup and just print a warning.
 221                  */
 222 #ifndef CONFIG_PREEMPT
 223                 WARN_ON_ONCE(1);
 224                 return 0;
 225 #endif
 226                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 227                     irqs_disabled()) {
 228                         WARN_ON_ONCE(1);
 229                         return 0;
 230                 }
 231                 rcu_barrier();
 232                 rcu_barrier_sched();
 233                 rcu_barrier_bh();
 234                 debug_object_activate(head, &rcuhead_debug_descr);
 235                 return 1;
 236         default:
 237                 return 0;
 238         }
 239 }
 240
 241 /*
 242  * fixup_free is called when:
 243  * - an active object is freed
 244  */
 245 static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
 246 {
 247         struct rcu_head *head = addr;
 248
 249         switch (state) {
 250         case ODEBUG_STATE_ACTIVE:
 251                 /*
 252                  * Ensure that queued callbacks are all executed.
 253                  * If we detect that we are nested in a RCU read-side critical
 254                  * section, we should simply fail, otherwise we would deadlock.
 255                  * In !PREEMPT configurations, there is no way to tell if we are
 256                  * in a RCU read-side critical section or not, so we never
 257                  * attempt any fixup and just print a warning.
 258                  */
 259 #ifndef CONFIG_PREEMPT
 260                 WARN_ON_ONCE(1);
 261                 return 0;
 262 #endif
 263                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 264                     irqs_disabled()) {
 265                         WARN_ON_ONCE(1);
 266                         return 0;
 267                 }
 268                 rcu_barrier();
 269                 rcu_barrier_sched();
 270                 rcu_barrier_bh();
 271                 debug_object_free(head, &rcuhead_debug_descr);
 272                 return 1;
 273         default:
 274                 return 0;
 275         }
 276 }
 277
 278 /**
 279  * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
 280  * @head: pointer to rcu_head structure to be initialized
 281  *
 282  * This function informs debugobjects of a new rcu_head structure that
 283  * has been allocated as an auto variable on the stack.  This function
 284  * is not required for rcu_head structures that are statically defined or
 285  * that are dynamically allocated on the heap.  This function has no
 286  * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 287  */
 288 void init_rcu_head_on_stack(struct rcu_head *head)
 289 {
 290         debug_object_init_on_stack(head, &rcuhead_debug_descr);
 291 }
 292 EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
 293
 294 /**
 295  * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
 296  * @head: pointer to rcu_head structure to be initialized
 297  *
 298  * This function informs debugobjects that an on-stack rcu_head structure
 299  * is about to go out of scope.  As with init_rcu_head_on_stack(), this
 300  * function is not required for rcu_head structures that are statically
 301  * defined or that are dynamically allocated on the heap.  Also as with
 302  * init_rcu_head_on_stack(), this function has no effect for
 303  * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 304  */
 305 void destroy_rcu_head_on_stack(struct rcu_head *head)
 306 {
 307         debug_object_free(head, &rcuhead_debug_descr);
 308 }
 309 EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
 310
 311 struct debug_obj_descr rcuhead_debug_descr = {
 312         .name = "rcu_head",
 313         .fixup_init = rcuhead_fixup_init,
 314         .fixup_activate = rcuhead_fixup_activate,
 315         .fixup_free = rcuhead_fixup_free,
 316 };
 317 EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
 318 #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */