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 #include <linux/delay.h>
  49 #include <linux/module.h>
  50
  51 #define CREATE_TRACE_POINTS
  52 #include <trace/events/rcu.h>
  53
  54 #include "rcu.h"
  55
  56 module_param(rcu_expedited, int, 0);
  57
  58 #ifdef CONFIG_PREEMPT_RCU
  59
  60 /*
  61  * Preemptible RCU implementation for rcu_read_lock().
  62  * Just increment ->rcu_read_lock_nesting, shared state will be updated
  63  * if we block.
  64  */
  65 void __rcu_read_lock(void)
  66 {
  67         current->rcu_read_lock_nesting++;
  68         barrier();  /* critical section after entry code. */
  69 }
  70 EXPORT_SYMBOL_GPL(__rcu_read_lock);
  71
  72 /*
  73  * Preemptible RCU implementation for rcu_read_unlock().
  74  * Decrement ->rcu_read_lock_nesting.  If the result is zero (outermost
  75  * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
  76  * invoke rcu_read_unlock_special() to clean up after a context switch
  77  * in an RCU read-side critical section and other special cases.
  78  */
  79 void __rcu_read_unlock(void)
  80 {
  81         struct task_struct *t = current;
  82
  83         if (t->rcu_read_lock_nesting != 1) {
  84                 --t->rcu_read_lock_nesting;
  85         } else {
  86                 barrier();  /* critical section before exit code. */
  87                 t->rcu_read_lock_nesting = INT_MIN;
  88 #ifdef CONFIG_PROVE_RCU_DELAY
  89                 udelay(10); /* Make preemption more probable. */
  90 #endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
  91                 barrier();  /* assign before ->rcu_read_unlock_special load */
  92                 if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
  93                         rcu_read_unlock_special(t);
  94                 barrier();  /* ->rcu_read_unlock_special load before assign */
  95                 t->rcu_read_lock_nesting = 0;
  96         }
  97 #ifdef CONFIG_PROVE_LOCKING
  98         {
  99                 int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);
 100
 101                 WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
 102         }
 103 #endif /* #ifdef CONFIG_PROVE_LOCKING */
 104 }
 105 EXPORT_SYMBOL_GPL(__rcu_read_unlock);
 106
 107 /*
 108  * Check for a task exiting while in a preemptible-RCU read-side
 109  * critical section, clean up if so.  No need to issue warnings,
 110  * as debug_check_no_locks_held() already does this if lockdep
 111  * is enabled.
 112  */
 113 void exit_rcu(void)
 114 {
 115         struct task_struct *t = current;
 116
 117         if (likely(list_empty(&current->rcu_node_entry)))
 118                 return;
 119         t->rcu_read_lock_nesting = 1;
 120         barrier();
 121         t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
 122         __rcu_read_unlock();
 123 }
 124
 125 #else /* #ifdef CONFIG_PREEMPT_RCU */
 126
 127 void exit_rcu(void)
 128 {
 129 }
 130
 131 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
 132
 133 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 134 static struct lock_class_key rcu_lock_key;
 135 struct lockdep_map rcu_lock_map =
 136         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
 137 EXPORT_SYMBOL_GPL(rcu_lock_map);
 138
 139 static struct lock_class_key rcu_bh_lock_key;
 140 struct lockdep_map rcu_bh_lock_map =
 141         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
 142 EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
 143
 144 static struct lock_class_key rcu_sched_lock_key;
 145 struct lockdep_map rcu_sched_lock_map =
 146         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
 147 EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
 148 #endif
 149
 150 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 151
 152 int debug_lockdep_rcu_enabled(void)
 153 {
 154         return rcu_scheduler_active && debug_locks &&
 155                current->lockdep_recursion == 0;
 156 }
 157 EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
 158
 159 /**
 160  * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
 161  *
 162  * Check for bottom half being disabled, which covers both the
 163  * CONFIG_PROVE_RCU and not cases.  Note that if someone uses
 164  * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
 165  * will show the situation.  This is useful for debug checks in functions
 166  * that require that they be called within an RCU read-side critical
 167  * section.
 168  *
 169  * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
 170  *
 171  * Note that rcu_read_lock() is disallowed if the CPU is either idle or
 172  * offline from an RCU perspective, so check for those as well.
 173  */
 174 int rcu_read_lock_bh_held(void)
 175 {
 176         if (!debug_lockdep_rcu_enabled())
 177                 return 1;
 178         if (rcu_is_cpu_idle())
 179                 return 0;
 180         if (!rcu_lockdep_current_cpu_online())
 181                 return 0;
 182         return in_softirq() || irqs_disabled();
 183 }
 184 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
 185
 186 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 187
 188 struct rcu_synchronize {
 189         struct rcu_head head;
 190         struct completion completion;
 191 };
 192
 193 /*
 194  * Awaken the corresponding synchronize_rcu() instance now that a
 195  * grace period has elapsed.
 196  */
 197 static void wakeme_after_rcu(struct rcu_head  *head)
 198 {
 199         struct rcu_synchronize *rcu;
 200
 201         rcu = container_of(head, struct rcu_synchronize, head);
 202         complete(&rcu->completion);
 203 }
 204
 205 void wait_rcu_gp(call_rcu_func_t crf)
 206 {
 207         struct rcu_synchronize rcu;
 208
 209         init_rcu_head_on_stack(&rcu.head);
 210         init_completion(&rcu.completion);
 211         /* Will wake me after RCU finished. */
 212         crf(&rcu.head, wakeme_after_rcu);
 213         /* Wait for it. */
 214         wait_for_completion(&rcu.completion);
 215         destroy_rcu_head_on_stack(&rcu.head);
 216 }
 217 EXPORT_SYMBOL_GPL(wait_rcu_gp);
 218
 219 #ifdef CONFIG_PROVE_RCU
 220 /*
 221  * wrapper function to avoid #include problems.
 222  */
 223 int rcu_my_thread_group_empty(void)
 224 {
 225         return thread_group_empty(current);
 226 }
 227 EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
 228 #endif /* #ifdef CONFIG_PROVE_RCU */
 229
 230 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
 231 static inline void debug_init_rcu_head(struct rcu_head *head)
 232 {
 233         debug_object_init(head, &rcuhead_debug_descr);
 234 }
 235
 236 static inline void debug_rcu_head_free(struct rcu_head *head)
 237 {
 238         debug_object_free(head, &rcuhead_debug_descr);
 239 }
 240
 241 /*
 242  * fixup_init is called when:
 243  * - an active object is initialized
 244  */
 245 static int rcuhead_fixup_init(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_init(head, &rcuhead_debug_descr);
 272                 return 1;
 273         default:
 274                 return 0;
 275         }
 276 }
 277
 278 /*
 279  * fixup_activate is called when:
 280  * - an active object is activated
 281  * - an unknown object is activated (might be a statically initialized object)
 282  * Activation is performed internally by call_rcu().
 283  */
 284 static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
 285 {
 286         struct rcu_head *head = addr;
 287
 288         switch (state) {
 289
 290         case ODEBUG_STATE_NOTAVAILABLE:
 291                 /*
 292                  * This is not really a fixup. We just make sure that it is
 293                  * tracked in the object tracker.
 294                  */
 295                 debug_object_init(head, &rcuhead_debug_descr);
 296                 debug_object_activate(head, &rcuhead_debug_descr);
 297                 return 0;
 298
 299         case ODEBUG_STATE_ACTIVE:
 300                 /*
 301                  * Ensure that queued callbacks are all executed.
 302                  * If we detect that we are nested in a RCU read-side critical
 303                  * section, we should simply fail, otherwise we would deadlock.
 304                  * In !PREEMPT configurations, there is no way to tell if we are
 305                  * in a RCU read-side critical section or not, so we never
 306                  * attempt any fixup and just print a warning.
 307                  */
 308 #ifndef CONFIG_PREEMPT
 309                 WARN_ON_ONCE(1);
 310                 return 0;
 311 #endif
 312                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 313                     irqs_disabled()) {
 314                         WARN_ON_ONCE(1);
 315                         return 0;
 316                 }
 317                 rcu_barrier();
 318                 rcu_barrier_sched();
 319                 rcu_barrier_bh();
 320                 debug_object_activate(head, &rcuhead_debug_descr);
 321                 return 1;
 322         default:
 323                 return 0;
 324         }
 325 }
 326
 327 /*
 328  * fixup_free is called when:
 329  * - an active object is freed
 330  */
 331 static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
 332 {
 333         struct rcu_head *head = addr;
 334
 335         switch (state) {
 336         case ODEBUG_STATE_ACTIVE:
 337                 /*
 338                  * Ensure that queued callbacks are all executed.
 339                  * If we detect that we are nested in a RCU read-side critical
 340                  * section, we should simply fail, otherwise we would deadlock.
 341                  * In !PREEMPT configurations, there is no way to tell if we are
 342                  * in a RCU read-side critical section or not, so we never
 343                  * attempt any fixup and just print a warning.
 344                  */
 345 #ifndef CONFIG_PREEMPT
 346                 WARN_ON_ONCE(1);
 347                 return 0;
 348 #endif
 349                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 350                     irqs_disabled()) {
 351                         WARN_ON_ONCE(1);
 352                         return 0;
 353                 }
 354                 rcu_barrier();
 355                 rcu_barrier_sched();
 356                 rcu_barrier_bh();
 357                 debug_object_free(head, &rcuhead_debug_descr);
 358                 return 1;
 359         default:
 360                 return 0;
 361         }
 362 }
 363
 364 /**
 365  * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
 366  * @head: pointer to rcu_head structure to be initialized
 367  *
 368  * This function informs debugobjects of a new rcu_head structure that
 369  * has been allocated as an auto variable on the stack.  This function
 370  * is not required for rcu_head structures that are statically defined or
 371  * that are dynamically allocated on the heap.  This function has no
 372  * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 373  */
 374 void init_rcu_head_on_stack(struct rcu_head *head)
 375 {
 376         debug_object_init_on_stack(head, &rcuhead_debug_descr);
 377 }
 378 EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
 379
 380 /**
 381  * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
 382  * @head: pointer to rcu_head structure to be initialized
 383  *
 384  * This function informs debugobjects that an on-stack rcu_head structure
 385  * is about to go out of scope.  As with init_rcu_head_on_stack(), this
 386  * function is not required for rcu_head structures that are statically
 387  * defined or that are dynamically allocated on the heap.  Also as with
 388  * init_rcu_head_on_stack(), this function has no effect for
 389  * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 390  */
 391 void destroy_rcu_head_on_stack(struct rcu_head *head)
 392 {
 393         debug_object_free(head, &rcuhead_debug_descr);
 394 }
 395 EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
 396
 397 struct debug_obj_descr rcuhead_debug_descr = {
 398         .name = "rcu_head",
 399         .fixup_init = rcuhead_fixup_init,
 400         .fixup_activate = rcuhead_fixup_activate,
 401         .fixup_free = rcuhead_fixup_free,
 402 };
 403 EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
 404 #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
 405
 406 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
 407 void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp)
 408 {
 409         trace_rcu_torture_read(rcutorturename, rhp);
 410 }
 411 EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
 412 #else
 413 #define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
 414 #endif