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/export.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  * Note that rcu_read_lock() is disallowed if the CPU is either idle or
  93  * offline from an RCU perspective, so check for those as well.
  94  */
  95 int rcu_read_lock_bh_held(void)
  96 {
  97         if (!debug_lockdep_rcu_enabled())
  98                 return 1;
  99         if (rcu_is_cpu_idle())
 100                 return 0;
 101         if (!rcu_lockdep_current_cpu_online())
 102                 return 0;
 103         return in_softirq() || irqs_disabled();
 104 }
 105 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
 106
 107 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 108
 109 struct rcu_synchronize {
 110         struct rcu_head head;
 111         struct completion completion;
 112 };
 113
 114 /*
 115  * Awaken the corresponding synchronize_rcu() instance now that a
 116  * grace period has elapsed.
 117  */
 118 static 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 }
 125
 126 void wait_rcu_gp(call_rcu_func_t crf)
 127 {
 128         struct rcu_synchronize rcu;
 129
 130         init_rcu_head_on_stack(&rcu.head);
 131         init_completion(&rcu.completion);
 132         /* Will wake me after RCU finished. */
 133         crf(&rcu.head, wakeme_after_rcu);
 134         /* Wait for it. */
 135         wait_for_completion(&rcu.completion);
 136         destroy_rcu_head_on_stack(&rcu.head);
 137 }
 138 EXPORT_SYMBOL_GPL(wait_rcu_gp);
 139
 140 #ifdef CONFIG_PROVE_RCU
 141 /*
 142  * wrapper function to avoid #include problems.
 143  */
 144 int rcu_my_thread_group_empty(void)
 145 {
 146         return thread_group_empty(current);
 147 }
 148 EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
 149 #endif /* #ifdef CONFIG_PROVE_RCU */
 150
 151 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
 152 static inline void debug_init_rcu_head(struct rcu_head *head)
 153 {
 154         debug_object_init(head, &rcuhead_debug_descr);
 155 }
 156
 157 static inline void debug_rcu_head_free(struct rcu_head *head)
 158 {
 159         debug_object_free(head, &rcuhead_debug_descr);
 160 }
 161
 162 /*
 163  * fixup_init is called when:
 164  * - an active object is initialized
 165  */
 166 static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
 167 {
 168         struct rcu_head *head = addr;
 169
 170         switch (state) {
 171         case ODEBUG_STATE_ACTIVE:
 172                 /*
 173                  * Ensure that queued callbacks are all executed.
 174                  * If we detect that we are nested in a RCU read-side critical
 175                  * section, we should simply fail, otherwise we would deadlock.
 176                  * In !PREEMPT configurations, there is no way to tell if we are
 177                  * in a RCU read-side critical section or not, so we never
 178                  * attempt any fixup and just print a warning.
 179                  */
 180 #ifndef CONFIG_PREEMPT
 181                 WARN_ON_ONCE(1);
 182                 return 0;
 183 #endif
 184                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 185                     irqs_disabled()) {
 186                         WARN_ON_ONCE(1);
 187                         return 0;
 188                 }
 189                 rcu_barrier();
 190                 rcu_barrier_sched();
 191                 rcu_barrier_bh();
 192                 debug_object_init(head, &rcuhead_debug_descr);
 193                 return 1;
 194         default:
 195                 return 0;
 196         }
 197 }
 198
 199 /*
 200  * fixup_activate is called when:
 201  * - an active object is activated
 202  * - an unknown object is activated (might be a statically initialized object)
 203  * Activation is performed internally by call_rcu().
 204  */
 205 static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
 206 {
 207         struct rcu_head *head = addr;
 208
 209         switch (state) {
 210
 211         case ODEBUG_STATE_NOTAVAILABLE:
 212                 /*
 213                  * This is not really a fixup. We just make sure that it is
 214                  * tracked in the object tracker.
 215                  */
 216                 debug_object_init(head, &rcuhead_debug_descr);
 217                 debug_object_activate(head, &rcuhead_debug_descr);
 218                 return 0;
 219
 220         case ODEBUG_STATE_ACTIVE:
 221                 /*
 222                  * Ensure that queued callbacks are all executed.
 223                  * If we detect that we are nested in a RCU read-side critical
 224                  * section, we should simply fail, otherwise we would deadlock.
 225                  * In !PREEMPT configurations, there is no way to tell if we are
 226                  * in a RCU read-side critical section or not, so we never
 227                  * attempt any fixup and just print a warning.
 228                  */
 229 #ifndef CONFIG_PREEMPT
 230                 WARN_ON_ONCE(1);
 231                 return 0;
 232 #endif
 233                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 234                     irqs_disabled()) {
 235                         WARN_ON_ONCE(1);
 236                         return 0;
 237                 }
 238                 rcu_barrier();
 239                 rcu_barrier_sched();
 240                 rcu_barrier_bh();
 241                 debug_object_activate(head, &rcuhead_debug_descr);
 242                 return 1;
 243         default:
 244                 return 0;
 245         }
 246 }
 247
 248 /*
 249  * fixup_free is called when:
 250  * - an active object is freed
 251  */
 252 static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
 253 {
 254         struct rcu_head *head = addr;
 255
 256         switch (state) {
 257         case ODEBUG_STATE_ACTIVE:
 258                 /*
 259                  * Ensure that queued callbacks are all executed.
 260                  * If we detect that we are nested in a RCU read-side critical
 261                  * section, we should simply fail, otherwise we would deadlock.
 262                  * In !PREEMPT configurations, there is no way to tell if we are
 263                  * in a RCU read-side critical section or not, so we never
 264                  * attempt any fixup and just print a warning.
 265                  */
 266 #ifndef CONFIG_PREEMPT
 267                 WARN_ON_ONCE(1);
 268                 return 0;
 269 #endif
 270                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 271                     irqs_disabled()) {
 272                         WARN_ON_ONCE(1);
 273                         return 0;
 274                 }
 275                 rcu_barrier();
 276                 rcu_barrier_sched();
 277                 rcu_barrier_bh();
 278                 debug_object_free(head, &rcuhead_debug_descr);
 279                 return 1;
 280         default:
 281                 return 0;
 282         }
 283 }
 284
 285 /**
 286  * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
 287  * @head: pointer to rcu_head structure to be initialized
 288  *
 289  * This function informs debugobjects of a new rcu_head structure that
 290  * has been allocated as an auto variable on the stack.  This function
 291  * is not required for rcu_head structures that are statically defined or
 292  * that are dynamically allocated on the heap.  This function has no
 293  * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 294  */
 295 void init_rcu_head_on_stack(struct rcu_head *head)
 296 {
 297         debug_object_init_on_stack(head, &rcuhead_debug_descr);
 298 }
 299 EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
 300
 301 /**
 302  * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
 303  * @head: pointer to rcu_head structure to be initialized
 304  *
 305  * This function informs debugobjects that an on-stack rcu_head structure
 306  * is about to go out of scope.  As with init_rcu_head_on_stack(), this
 307  * function is not required for rcu_head structures that are statically
 308  * defined or that are dynamically allocated on the heap.  Also as with
 309  * init_rcu_head_on_stack(), this function has no effect for
 310  * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 311  */
 312 void destroy_rcu_head_on_stack(struct rcu_head *head)
 313 {
 314         debug_object_free(head, &rcuhead_debug_descr);
 315 }
 316 EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
 317
 318 struct debug_obj_descr rcuhead_debug_descr = {
 319         .name = "rcu_head",
 320         .fixup_init = rcuhead_fixup_init,
 321         .fixup_activate = rcuhead_fixup_activate,
 322         .fixup_free = rcuhead_fixup_free,
 323 };
 324 EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
 325 #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
 326
 327 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
 328 void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp)
 329 {
 330         trace_rcu_torture_read(rcutorturename, rhp);
 331 }
 332 EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
 333 #else
 334 #define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
 335 #endif