include/linux/rcupdate.h

   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  * Author: Dipankar Sarma <dipankar@in.ibm.com>
  21  *
  22  * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
  23  * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
  24  * Papers:
  25  * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
  26  * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
  27  *
  28  * For detailed explanation of Read-Copy Update mechanism see -
  29  *              http://lse.sourceforge.net/locking/rcupdate.html
  30  *
  31  */
  32
  33 #ifndef __LINUX_RCUPDATE_H
  34 #define __LINUX_RCUPDATE_H
  35
  36 #include <linux/cache.h>
  37 #include <linux/spinlock.h>
  38 #include <linux/threads.h>
  39 #include <linux/cpumask.h>
  40 #include <linux/seqlock.h>
  41 #include <linux/lockdep.h>
  42 #include <linux/completion.h>
  43
  44 #ifdef CONFIG_RCU_TORTURE_TEST
  45 extern int rcutorture_runnable; /* for sysctl */
  46 #endif /* #ifdef CONFIG_RCU_TORTURE_TEST */
  47
  48 /**
  49  * struct rcu_head - callback structure for use with RCU
  50  * @next: next update requests in a list
  51  * @func: actual update function to call after the grace period.
  52  */
  53 struct rcu_head {
  54         struct rcu_head *next;
  55         void (*func)(struct rcu_head *head);
  56 };
  57
  58 /* Exported common interfaces */
  59 extern void synchronize_rcu_bh(void);
  60 extern void synchronize_sched(void);
  61 extern void rcu_barrier(void);
  62 extern void rcu_barrier_bh(void);
  63 extern void rcu_barrier_sched(void);
  64 extern void synchronize_sched_expedited(void);
  65 extern int sched_expedited_torture_stats(char *page);
  66
  67 /* Internal to kernel */
  68 extern void rcu_init(void);
  69 extern int rcu_scheduler_active;
  70 extern void rcu_scheduler_starting(void);
  71
  72 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
  73 #include <linux/rcutree.h>
  74 #elif defined(CONFIG_TINY_RCU)
  75 #include <linux/rcutiny.h>
  76 #else
  77 #error "Unknown RCU implementation specified to kernel configuration"
  78 #endif
  79
  80 #define RCU_HEAD_INIT   { .next = NULL, .func = NULL }
  81 #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
  82 #define INIT_RCU_HEAD(ptr) do { \
  83        (ptr)->next = NULL; (ptr)->func = NULL; \
  84 } while (0)
  85
  86 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  87
  88 extern struct lockdep_map rcu_lock_map;
  89 # define rcu_read_acquire() \
  90                 lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
  91 # define rcu_read_release()     lock_release(&rcu_lock_map, 1, _THIS_IP_)
  92
  93 extern struct lockdep_map rcu_bh_lock_map;
  94 # define rcu_read_acquire_bh() \
  95                 lock_acquire(&rcu_bh_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
  96 # define rcu_read_release_bh()  lock_release(&rcu_bh_lock_map, 1, _THIS_IP_)
  97
  98 extern struct lockdep_map rcu_sched_lock_map;
  99 # define rcu_read_acquire_sched() \
 100                 lock_acquire(&rcu_sched_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
 101 # define rcu_read_release_sched() \
 102                 lock_release(&rcu_sched_lock_map, 1, _THIS_IP_)
 103
 104 extern int debug_lockdep_rcu_enabled(void);
 105
 106 /**
 107  * rcu_read_lock_held - might we be in RCU read-side critical section?
 108  *
 109  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
 110  * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
 111  * this assumes we are in an RCU read-side critical section unless it can
 112  * prove otherwise.
 113  *
 114  * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
 115  * and while lockdep is disabled.
 116  */
 117 static inline int rcu_read_lock_held(void)
 118 {
 119         if (!debug_lockdep_rcu_enabled())
 120                 return 1;
 121         return lock_is_held(&rcu_lock_map);
 122 }
 123
 124 /*
 125  * rcu_read_lock_bh_held() is defined out of line to avoid #include-file
 126  * hell.
 127  */
 128 extern int rcu_read_lock_bh_held(void);
 129
 130 /**
 131  * rcu_read_lock_sched_held - might we be in RCU-sched read-side critical section?
 132  *
 133  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
 134  * RCU-sched read-side critical section.  In absence of
 135  * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
 136  * critical section unless it can prove otherwise.  Note that disabling
 137  * of preemption (including disabling irqs) counts as an RCU-sched
 138  * read-side critical section.
 139  *
 140  * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
 141  * and while lockdep is disabled.
 142  */
 143 #ifdef CONFIG_PREEMPT
 144 static inline int rcu_read_lock_sched_held(void)
 145 {
 146         int lockdep_opinion = 0;
 147
 148         if (!debug_lockdep_rcu_enabled())
 149                 return 1;
 150         if (debug_locks)
 151                 lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
 152         return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
 153 }
 154 #else /* #ifdef CONFIG_PREEMPT */
 155 static inline int rcu_read_lock_sched_held(void)
 156 {
 157         return 1;
 158 }
 159 #endif /* #else #ifdef CONFIG_PREEMPT */
 160
 161 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 162
 163 # define rcu_read_acquire()             do { } while (0)
 164 # define rcu_read_release()             do { } while (0)
 165 # define rcu_read_acquire_bh()          do { } while (0)
 166 # define rcu_read_release_bh()          do { } while (0)
 167 # define rcu_read_acquire_sched()       do { } while (0)
 168 # define rcu_read_release_sched()       do { } while (0)
 169
 170 static inline int rcu_read_lock_held(void)
 171 {
 172         return 1;
 173 }
 174
 175 static inline int rcu_read_lock_bh_held(void)
 176 {
 177         return 1;
 178 }
 179
 180 #ifdef CONFIG_PREEMPT
 181 static inline int rcu_read_lock_sched_held(void)
 182 {
 183         return !rcu_scheduler_active || preempt_count() != 0 || irqs_disabled();
 184 }
 185 #else /* #ifdef CONFIG_PREEMPT */
 186 static inline int rcu_read_lock_sched_held(void)
 187 {
 188         return 1;
 189 }
 190 #endif /* #else #ifdef CONFIG_PREEMPT */
 191
 192 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 193
 194 #ifdef CONFIG_PROVE_RCU
 195
 196 extern int rcu_my_thread_group_empty(void);
 197
 198 #define __do_rcu_dereference_check(c)                                   \
 199         do {                                                            \
 200                 static bool __warned;                                   \
 201                 if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
 202                         __warned = true;                                \
 203                         lockdep_rcu_dereference(__FILE__, __LINE__);    \
 204                 }                                                       \
 205         } while (0)
 206
 207 /**
 208  * rcu_dereference_check - rcu_dereference with debug checking
 209  * @p: The pointer to read, prior to dereferencing
 210  * @c: The conditions under which the dereference will take place
 211  *
 212  * Do an rcu_dereference(), but check that the conditions under which the
 213  * dereference will take place are correct.  Typically the conditions indicate
 214  * the various locking conditions that should be held at that point.  The check
 215  * should return true if the conditions are satisfied.
 216  *
 217  * For example:
 218  *
 219  *      bar = rcu_dereference_check(foo->bar, rcu_read_lock_held() ||
 220  *                                            lockdep_is_held(&foo->lock));
 221  *
 222  * could be used to indicate to lockdep that foo->bar may only be dereferenced
 223  * if either the RCU read lock is held, or that the lock required to replace
 224  * the bar struct at foo->bar is held.
 225  *
 226  * Note that the list of conditions may also include indications of when a lock
 227  * need not be held, for example during initialisation or destruction of the
 228  * target struct:
 229  *
 230  *      bar = rcu_dereference_check(foo->bar, rcu_read_lock_held() ||
 231  *                                            lockdep_is_held(&foo->lock) ||
 232  *                                            atomic_read(&foo->usage) == 0);
 233  */
 234 #define rcu_dereference_check(p, c) \
 235         ({ \
 236                 __do_rcu_dereference_check(c); \
 237                 rcu_dereference_raw(p); \
 238         })
 239
 240 /**
 241  * rcu_dereference_protected - fetch RCU pointer when updates prevented
 242  *
 243  * Return the value of the specified RCU-protected pointer, but omit
 244  * both the smp_read_barrier_depends() and the ACCESS_ONCE().  This
 245  * is useful in cases where update-side locks prevent the value of the
 246  * pointer from changing.  Please note that this primitive does -not-
 247  * prevent the compiler from repeating this reference or combining it
 248  * with other references, so it should not be used without protection
 249  * of appropriate locks.
 250  */
 251 #define rcu_dereference_protected(p, c) \
 252         ({ \
 253                 __do_rcu_dereference_check(c); \
 254                 (p); \
 255         })
 256
 257 #else /* #ifdef CONFIG_PROVE_RCU */
 258
 259 #define rcu_dereference_check(p, c)     rcu_dereference_raw(p)
 260 #define rcu_dereference_protected(p, c) (p)
 261
 262 #endif /* #else #ifdef CONFIG_PROVE_RCU */
 263
 264 /**
 265  * rcu_access_pointer - fetch RCU pointer with no dereferencing
 266  *
 267  * Return the value of the specified RCU-protected pointer, but omit the
 268  * smp_read_barrier_depends() and keep the ACCESS_ONCE().  This is useful
 269  * when the value of this pointer is accessed, but the pointer is not
 270  * dereferenced, for example, when testing an RCU-protected pointer against
 271  * NULL.  This may also be used in cases where update-side locks prevent
 272  * the value of the pointer from changing, but rcu_dereference_protected()
 273  * is a lighter-weight primitive for this use case.
 274  */
 275 #define rcu_access_pointer(p)   ACCESS_ONCE(p)
 276
 277 /**
 278  * rcu_read_lock - mark the beginning of an RCU read-side critical section.
 279  *
 280  * When synchronize_rcu() is invoked on one CPU while other CPUs
 281  * are within RCU read-side critical sections, then the
 282  * synchronize_rcu() is guaranteed to block until after all the other
 283  * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
 284  * on one CPU while other CPUs are within RCU read-side critical
 285  * sections, invocation of the corresponding RCU callback is deferred
 286  * until after the all the other CPUs exit their critical sections.
 287  *
 288  * Note, however, that RCU callbacks are permitted to run concurrently
 289  * with RCU read-side critical sections.  One way that this can happen
 290  * is via the following sequence of events: (1) CPU 0 enters an RCU
 291  * read-side critical section, (2) CPU 1 invokes call_rcu() to register
 292  * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
 293  * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
 294  * callback is invoked.  This is legal, because the RCU read-side critical
 295  * section that was running concurrently with the call_rcu() (and which
 296  * therefore might be referencing something that the corresponding RCU
 297  * callback would free up) has completed before the corresponding
 298  * RCU callback is invoked.
 299  *
 300  * RCU read-side critical sections may be nested.  Any deferred actions
 301  * will be deferred until the outermost RCU read-side critical section
 302  * completes.
 303  *
 304  * It is illegal to block while in an RCU read-side critical section.
 305  */
 306 static inline void rcu_read_lock(void)
 307 {
 308         __rcu_read_lock();
 309         __acquire(RCU);
 310         rcu_read_acquire();
 311 }
 312
 313 /*
 314  * So where is rcu_write_lock()?  It does not exist, as there is no
 315  * way for writers to lock out RCU readers.  This is a feature, not
 316  * a bug -- this property is what provides RCU's performance benefits.
 317  * Of course, writers must coordinate with each other.  The normal
 318  * spinlock primitives work well for this, but any other technique may be
 319  * used as well.  RCU does not care how the writers keep out of each
 320  * others' way, as long as they do so.
 321  */
 322
 323 /**
 324  * rcu_read_unlock - marks the end of an RCU read-side critical section.
 325  *
 326  * See rcu_read_lock() for more information.
 327  */
 328 static inline void rcu_read_unlock(void)
 329 {
 330         rcu_read_release();
 331         __release(RCU);
 332         __rcu_read_unlock();
 333 }
 334
 335 /**
 336  * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
 337  *
 338  * This is equivalent of rcu_read_lock(), but to be used when updates
 339  * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
 340  * consider completion of a softirq handler to be a quiescent state,
 341  * a process in RCU read-side critical section must be protected by
 342  * disabling softirqs. Read-side critical sections in interrupt context
 343  * can use just rcu_read_lock().
 344  *
 345  */
 346 static inline void rcu_read_lock_bh(void)
 347 {
 348         __rcu_read_lock_bh();
 349         __acquire(RCU_BH);
 350         rcu_read_acquire_bh();
 351 }
 352
 353 /*
 354  * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
 355  *
 356  * See rcu_read_lock_bh() for more information.
 357  */
 358 static inline void rcu_read_unlock_bh(void)
 359 {
 360         rcu_read_release_bh();
 361         __release(RCU_BH);
 362         __rcu_read_unlock_bh();
 363 }
 364
 365 /**
 366  * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
 367  *
 368  * Should be used with either
 369  * - synchronize_sched()
 370  * or
 371  * - call_rcu_sched() and rcu_barrier_sched()
 372  * on the write-side to insure proper synchronization.
 373  */
 374 static inline void rcu_read_lock_sched(void)
 375 {
 376         preempt_disable();
 377         __acquire(RCU_SCHED);
 378         rcu_read_acquire_sched();
 379 }
 380
 381 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
 382 static inline notrace void rcu_read_lock_sched_notrace(void)
 383 {
 384         preempt_disable_notrace();
 385         __acquire(RCU_SCHED);
 386 }
 387
 388 /*
 389  * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
 390  *
 391  * See rcu_read_lock_sched for more information.
 392  */
 393 static inline void rcu_read_unlock_sched(void)
 394 {
 395         rcu_read_release_sched();
 396         __release(RCU_SCHED);
 397         preempt_enable();
 398 }
 399
 400 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
 401 static inline notrace void rcu_read_unlock_sched_notrace(void)
 402 {
 403         __release(RCU_SCHED);
 404         preempt_enable_notrace();
 405 }
 406
 407
 408 /**
 409  * rcu_dereference_raw - fetch an RCU-protected pointer
 410  *
 411  * The caller must be within some flavor of RCU read-side critical
 412  * section, or must be otherwise preventing the pointer from changing,
 413  * for example, by holding an appropriate lock.  This pointer may later
 414  * be safely dereferenced.  It is the caller's responsibility to have
 415  * done the right thing, as this primitive does no checking of any kind.
 416  *
 417  * Inserts memory barriers on architectures that require them
 418  * (currently only the Alpha), and, more importantly, documents
 419  * exactly which pointers are protected by RCU.
 420  */
 421 #define rcu_dereference_raw(p)  ({ \
 422                                 typeof(p) _________p1 = ACCESS_ONCE(p); \
 423                                 smp_read_barrier_depends(); \
 424                                 (_________p1); \
 425                                 })
 426
 427 /**
 428  * rcu_dereference - fetch an RCU-protected pointer, checking for RCU
 429  *
 430  * Makes rcu_dereference_check() do the dirty work.
 431  */
 432 #define rcu_dereference(p) \
 433         rcu_dereference_check(p, rcu_read_lock_held())
 434
 435 /**
 436  * rcu_dereference_bh - fetch an RCU-protected pointer, checking for RCU-bh
 437  *
 438  * Makes rcu_dereference_check() do the dirty work.
 439  */
 440 #define rcu_dereference_bh(p) \
 441                 rcu_dereference_check(p, rcu_read_lock_bh_held())
 442
 443 /**
 444  * rcu_dereference_sched - fetch RCU-protected pointer, checking for RCU-sched
 445  *
 446  * Makes rcu_dereference_check() do the dirty work.
 447  */
 448 #define rcu_dereference_sched(p) \
 449                 rcu_dereference_check(p, rcu_read_lock_sched_held())
 450
 451 /**
 452  * rcu_assign_pointer - assign (publicize) a pointer to a newly
 453  * initialized structure that will be dereferenced by RCU read-side
 454  * critical sections.  Returns the value assigned.
 455  *
 456  * Inserts memory barriers on architectures that require them
 457  * (pretty much all of them other than x86), and also prevents
 458  * the compiler from reordering the code that initializes the
 459  * structure after the pointer assignment.  More importantly, this
 460  * call documents which pointers will be dereferenced by RCU read-side
 461  * code.
 462  */
 463
 464 #define rcu_assign_pointer(p, v) \
 465         ({ \
 466                 if (!__builtin_constant_p(v) || \
 467                     ((v) != NULL)) \
 468                         smp_wmb(); \
 469                 (p) = (v); \
 470         })
 471
 472 /* Infrastructure to implement the synchronize_() primitives. */
 473
 474 struct rcu_synchronize {
 475         struct rcu_head head;
 476         struct completion completion;
 477 };
 478
 479 extern void wakeme_after_rcu(struct rcu_head  *head);
 480
 481 /**
 482  * call_rcu - Queue an RCU callback for invocation after a grace period.
 483  * @head: structure to be used for queueing the RCU updates.
 484  * @func: actual update function to be invoked after the grace period
 485  *
 486  * The update function will be invoked some time after a full grace
 487  * period elapses, in other words after all currently executing RCU
 488  * read-side critical sections have completed.  RCU read-side critical
 489  * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
 490  * and may be nested.
 491  */
 492 extern void call_rcu(struct rcu_head *head,
 493                               void (*func)(struct rcu_head *head));
 494
 495 /**
 496  * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
 497  * @head: structure to be used for queueing the RCU updates.
 498  * @func: actual update function to be invoked after the grace period
 499  *
 500  * The update function will be invoked some time after a full grace
 501  * period elapses, in other words after all currently executing RCU
 502  * read-side critical sections have completed. call_rcu_bh() assumes
 503  * that the read-side critical sections end on completion of a softirq
 504  * handler. This means that read-side critical sections in process
 505  * context must not be interrupted by softirqs. This interface is to be
 506  * used when most of the read-side critical sections are in softirq context.
 507  * RCU read-side critical sections are delimited by :
 508  *  - rcu_read_lock() and  rcu_read_unlock(), if in interrupt context.
 509  *  OR
 510  *  - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
 511  *  These may be nested.
 512  */
 513 extern void call_rcu_bh(struct rcu_head *head,
 514                         void (*func)(struct rcu_head *head));
 515
 516 #endif /* __LINUX_RCUPDATE_H */