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_PREEMPT_RCU
  55
  56 /*
  57  * Check for a task exiting while in a preemptible-RCU read-side
  58  * critical section, clean up if so.  No need to issue warnings,
  59  * as debug_check_no_locks_held() already does this if lockdep
  60  * is enabled.
  61  */
  62 void exit_rcu(void)
  63 {
  64         struct task_struct *t = current;
  65
  66         if (likely(list_empty(&current->rcu_node_entry)))
  67                 return;
  68         t->rcu_read_lock_nesting = 1;
  69         barrier();
  70         t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
  71         __rcu_read_unlock();
  72 }
  73
  74 #else /* #ifdef CONFIG_PREEMPT_RCU */
  75
  76 void exit_rcu(void)
  77 {
  78 }
  79
  80 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
  81
  82 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  83 static struct lock_class_key rcu_lock_key;
  84 struct lockdep_map rcu_lock_map =
  85         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
  86 EXPORT_SYMBOL_GPL(rcu_lock_map);
  87
  88 static struct lock_class_key rcu_bh_lock_key;
  89 struct lockdep_map rcu_bh_lock_map =
  90         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
  91 EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
  92
  93 static struct lock_class_key rcu_sched_lock_key;
  94 struct lockdep_map rcu_sched_lock_map =
  95         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
  96 EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
  97 #endif
  98
  99 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 100
 101 int debug_lockdep_rcu_enabled(void)
 102 {
 103         return rcu_scheduler_active && debug_locks &&
 104                current->lockdep_recursion == 0;
 105 }
 106 EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
 107
 108 /**
 109  * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
 110  *
 111  * Check for bottom half being disabled, which covers both the
 112  * CONFIG_PROVE_RCU and not cases.  Note that if someone uses
 113  * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
 114  * will show the situation.  This is useful for debug checks in functions
 115  * that require that they be called within an RCU read-side critical
 116  * section.
 117  *
 118  * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
 119  *
 120  * Note that rcu_read_lock() is disallowed if the CPU is either idle or
 121  * offline from an RCU perspective, so check for those as well.
 122  */
 123 int rcu_read_lock_bh_held(void)
 124 {
 125         if (!debug_lockdep_rcu_enabled())
 126                 return 1;
 127         if (rcu_is_cpu_idle())
 128                 return 0;
 129         if (!rcu_lockdep_current_cpu_online())
 130                 return 0;
 131         return in_softirq() || irqs_disabled();
 132 }
 133 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
 134
 135 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 136
 137 struct rcu_synchronize {
 138         struct rcu_head head;
 139         struct completion completion;
 140 };
 141
 142 /*
 143  * Awaken the corresponding synchronize_rcu() instance now that a
 144  * grace period has elapsed.
 145  */
 146 static void wakeme_after_rcu(struct rcu_head  *head)
 147 {
 148         struct rcu_synchronize *rcu;
 149
 150         rcu = container_of(head, struct rcu_synchronize, head);
 151         complete(&rcu->completion);
 152 }
 153
 154 void wait_rcu_gp(call_rcu_func_t crf)
 155 {
 156         struct rcu_synchronize rcu;
 157
 158         init_rcu_head_on_stack(&rcu.head);
 159         init_completion(&rcu.completion);
 160         /* Will wake me after RCU finished. */
 161         crf(&rcu.head, wakeme_after_rcu);
 162         /* Wait for it. */
 163         wait_for_completion(&rcu.completion);
 164         destroy_rcu_head_on_stack(&rcu.head);
 165 }
 166 EXPORT_SYMBOL_GPL(wait_rcu_gp);
 167
 168 #ifdef CONFIG_PROVE_RCU
 169 /*
 170  * wrapper function to avoid #include problems.
 171  */
 172 int rcu_my_thread_group_empty(void)
 173 {
 174         return thread_group_empty(current);
 175 }
 176 EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
 177 #endif /* #ifdef CONFIG_PROVE_RCU */
 178
 179 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
 180 static inline void debug_init_rcu_head(struct rcu_head *head)
 181 {
 182         debug_object_init(head, &rcuhead_debug_descr);
 183 }
 184
 185 static inline void debug_rcu_head_free(struct rcu_head *head)
 186 {
 187         debug_object_free(head, &rcuhead_debug_descr);
 188 }
 189
 190 /*
 191  * fixup_init is called when:
 192  * - an active object is initialized
 193  */
 194 static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
 195 {
 196         struct rcu_head *head = addr;
 197
 198         switch (state) {
 199         case ODEBUG_STATE_ACTIVE:
 200                 /*
 201                  * Ensure that queued callbacks are all executed.
 202                  * If we detect that we are nested in a RCU read-side critical
 203                  * section, we should simply fail, otherwise we would deadlock.
 204                  * In !PREEMPT configurations, there is no way to tell if we are
 205                  * in a RCU read-side critical section or not, so we never
 206                  * attempt any fixup and just print a warning.
 207                  */
 208 #ifndef CONFIG_PREEMPT
 209                 WARN_ON_ONCE(1);
 210                 return 0;
 211 #endif
 212                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 213                     irqs_disabled()) {
 214                         WARN_ON_ONCE(1);
 215                         return 0;
 216                 }
 217                 rcu_barrier();
 218                 rcu_barrier_sched();
 219                 rcu_barrier_bh();
 220                 debug_object_init(head, &rcuhead_debug_descr);
 221                 return 1;
 222         default:
 223                 return 0;
 224         }
 225 }
 226
 227 /*
 228  * fixup_activate is called when:
 229  * - an active object is activated
 230  * - an unknown object is activated (might be a statically initialized object)
 231  * Activation is performed internally by call_rcu().
 232  */
 233 static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
 234 {
 235         struct rcu_head *head = addr;
 236
 237         switch (state) {
 238
 239         case ODEBUG_STATE_NOTAVAILABLE:
 240                 /*
 241                  * This is not really a fixup. We just make sure that it is
 242                  * tracked in the object tracker.
 243                  */
 244                 debug_object_init(head, &rcuhead_debug_descr);
 245                 debug_object_activate(head, &rcuhead_debug_descr);
 246                 return 0;
 247
 248         case ODEBUG_STATE_ACTIVE:
 249                 /*
 250                  * Ensure that queued callbacks are all executed.
 251                  * If we detect that we are nested in a RCU read-side critical
 252                  * section, we should simply fail, otherwise we would deadlock.
 253                  * In !PREEMPT configurations, there is no way to tell if we are
 254                  * in a RCU read-side critical section or not, so we never
 255                  * attempt any fixup and just print a warning.
 256                  */
 257 #ifndef CONFIG_PREEMPT
 258                 WARN_ON_ONCE(1);
 259                 return 0;
 260 #endif
 261                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 262                     irqs_disabled()) {
 263                         WARN_ON_ONCE(1);
 264                         return 0;
 265                 }
 266                 rcu_barrier();
 267                 rcu_barrier_sched();
 268                 rcu_barrier_bh();
 269                 debug_object_activate(head, &rcuhead_debug_descr);
 270                 return 1;
 271         default:
 272                 return 0;
 273         }
 274 }
 275
 276 /*
 277  * fixup_free is called when:
 278  * - an active object is freed
 279  */
 280 static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
 281 {
 282         struct rcu_head *head = addr;
 283
 284         switch (state) {
 285         case ODEBUG_STATE_ACTIVE:
 286                 /*
 287                  * Ensure that queued callbacks are all executed.
 288                  * If we detect that we are nested in a RCU read-side critical
 289                  * section, we should simply fail, otherwise we would deadlock.
 290                  * In !PREEMPT configurations, there is no way to tell if we are
 291                  * in a RCU read-side critical section or not, so we never
 292                  * attempt any fixup and just print a warning.
 293                  */
 294 #ifndef CONFIG_PREEMPT
 295                 WARN_ON_ONCE(1);
 296                 return 0;
 297 #endif
 298                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 299                     irqs_disabled()) {
 300                         WARN_ON_ONCE(1);
 301                         return 0;
 302                 }
 303                 rcu_barrier();
 304                 rcu_barrier_sched();
 305                 rcu_barrier_bh();
 306                 debug_object_free(head, &rcuhead_debug_descr);
 307                 return 1;
 308         default:
 309                 return 0;
 310         }
 311 }
 312
 313 /**
 314  * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
 315  * @head: pointer to rcu_head structure to be initialized
 316  *
 317  * This function informs debugobjects of a new rcu_head structure that
 318  * has been allocated as an auto variable on the stack.  This function
 319  * is not required for rcu_head structures that are statically defined or
 320  * that are dynamically allocated on the heap.  This function has no
 321  * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 322  */
 323 void init_rcu_head_on_stack(struct rcu_head *head)
 324 {
 325         debug_object_init_on_stack(head, &rcuhead_debug_descr);
 326 }
 327 EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
 328
 329 /**
 330  * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
 331  * @head: pointer to rcu_head structure to be initialized
 332  *
 333  * This function informs debugobjects that an on-stack rcu_head structure
 334  * is about to go out of scope.  As with init_rcu_head_on_stack(), this
 335  * function is not required for rcu_head structures that are statically
 336  * defined or that are dynamically allocated on the heap.  Also as with
 337  * init_rcu_head_on_stack(), this function has no effect for
 338  * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 339  */
 340 void destroy_rcu_head_on_stack(struct rcu_head *head)
 341 {
 342         debug_object_free(head, &rcuhead_debug_descr);
 343 }
 344 EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
 345
 346 struct debug_obj_descr rcuhead_debug_descr = {
 347         .name = "rcu_head",
 348         .fixup_init = rcuhead_fixup_init,
 349         .fixup_activate = rcuhead_fixup_activate,
 350         .fixup_free = rcuhead_fixup_free,
 351 };
 352 EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
 353 #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
 354
 355 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
 356 void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp)
 357 {
 358         trace_rcu_torture_read(rcutorturename, rhp);
 359 }
 360 EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
 361 #else
 362 #define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
 363 #endif