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 rcu_barrier(void);
  60 extern void rcu_barrier_bh(void);
  61 extern void rcu_barrier_sched(void);
  62 extern void synchronize_sched_expedited(void);
  63 extern int sched_expedited_torture_stats(char *page);
  64
  65 /* Internal to kernel */
  66 extern void rcu_init(void);
  67
  68 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
  69 #include <linux/rcutree.h>
  70 #elif defined(CONFIG_TINY_RCU)
  71 #include <linux/rcutiny.h>
  72 #else
  73 #error "Unknown RCU implementation specified to kernel configuration"
  74 #endif
  75
  76 #define RCU_HEAD_INIT   { .next = NULL, .func = NULL }
  77 #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
  78 #define INIT_RCU_HEAD(ptr) do { \
  79        (ptr)->next = NULL; (ptr)->func = NULL; \
  80 } while (0)
  81
  82 static inline void init_rcu_head_on_stack(struct rcu_head *head)
  83 {
  84 }
  85
  86 static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
  87 {
  88 }
  89
  90 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  91
  92 extern struct lockdep_map rcu_lock_map;
  93 # define rcu_read_acquire() \
  94                 lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
  95 # define rcu_read_release()     lock_release(&rcu_lock_map, 1, _THIS_IP_)
  96
  97 extern struct lockdep_map rcu_bh_lock_map;
  98 # define rcu_read_acquire_bh() \
  99                 lock_acquire(&rcu_bh_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
 100 # define rcu_read_release_bh()  lock_release(&rcu_bh_lock_map, 1, _THIS_IP_)
 101
 102 extern struct lockdep_map rcu_sched_lock_map;
 103 # define rcu_read_acquire_sched() \
 104                 lock_acquire(&rcu_sched_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
 105 # define rcu_read_release_sched() \
 106                 lock_release(&rcu_sched_lock_map, 1, _THIS_IP_)
 107
 108 extern int debug_lockdep_rcu_enabled(void);
 109
 110 /**
 111  * rcu_read_lock_held - might we be in RCU read-side critical section?
 112  *
 113  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
 114  * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
 115  * this assumes we are in an RCU read-side critical section unless it can
 116  * prove otherwise.
 117  *
 118  * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
 119  * and while lockdep is disabled.
 120  */
 121 static inline int rcu_read_lock_held(void)
 122 {
 123         if (!debug_lockdep_rcu_enabled())
 124                 return 1;
 125         return lock_is_held(&rcu_lock_map);
 126 }
 127
 128 /*
 129  * rcu_read_lock_bh_held() is defined out of line to avoid #include-file
 130  * hell.
 131  */
 132 extern int rcu_read_lock_bh_held(void);
 133
 134 /**
 135  * rcu_read_lock_sched_held - might we be in RCU-sched read-side critical section?
 136  *
 137  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
 138  * RCU-sched read-side critical section.  In absence of
 139  * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
 140  * critical section unless it can prove otherwise.  Note that disabling
 141  * of preemption (including disabling irqs) counts as an RCU-sched
 142  * read-side critical section.
 143  *
 144  * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
 145  * and while lockdep is disabled.
 146  */
 147 #ifdef CONFIG_PREEMPT
 148 static inline int rcu_read_lock_sched_held(void)
 149 {
 150         int lockdep_opinion = 0;
 151
 152         if (!debug_lockdep_rcu_enabled())
 153                 return 1;
 154         if (debug_locks)
 155                 lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
 156         return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
 157 }
 158 #else /* #ifdef CONFIG_PREEMPT */
 159 static inline int rcu_read_lock_sched_held(void)
 160 {
 161         return 1;
 162 }
 163 #endif /* #else #ifdef CONFIG_PREEMPT */
 164
 165 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 166
 167 # define rcu_read_acquire()             do { } while (0)
 168 # define rcu_read_release()             do { } while (0)
 169 # define rcu_read_acquire_bh()          do { } while (0)
 170 # define rcu_read_release_bh()          do { } while (0)
 171 # define rcu_read_acquire_sched()       do { } while (0)
 172 # define rcu_read_release_sched()       do { } while (0)
 173
 174 static inline int rcu_read_lock_held(void)
 175 {
 176         return 1;
 177 }
 178
 179 static inline int rcu_read_lock_bh_held(void)
 180 {
 181         return 1;
 182 }
 183
 184 #ifdef CONFIG_PREEMPT
 185 static inline int rcu_read_lock_sched_held(void)
 186 {
 187         return preempt_count() != 0 || irqs_disabled();
 188 }
 189 #else /* #ifdef CONFIG_PREEMPT */
 190 static inline int rcu_read_lock_sched_held(void)
 191 {
 192         return 1;
 193 }
 194 #endif /* #else #ifdef CONFIG_PREEMPT */
 195
 196 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 197
 198 #ifdef CONFIG_PROVE_RCU
 199
 200 extern int rcu_my_thread_group_empty(void);
 201
 202 #define __do_rcu_dereference_check(c)                                   \
 203         do {                                                            \
 204                 static bool __warned;                                   \
 205                 if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
 206                         __warned = true;                                \
 207                         lockdep_rcu_dereference(__FILE__, __LINE__);    \
 208                 }                                                       \
 209         } while (0)
 210
 211 /**
 212  * rcu_dereference_check - rcu_dereference with debug checking
 213  * @p: The pointer to read, prior to dereferencing
 214  * @c: The conditions under which the dereference will take place
 215  *
 216  * Do an rcu_dereference(), but check that the conditions under which the
 217  * dereference will take place are correct.  Typically the conditions indicate
 218  * the various locking conditions that should be held at that point.  The check
 219  * should return true if the conditions are satisfied.
 220  *
 221  * For example:
 222  *
 223  *      bar = rcu_dereference_check(foo->bar, rcu_read_lock_held() ||
 224  *                                            lockdep_is_held(&foo->lock));
 225  *
 226  * could be used to indicate to lockdep that foo->bar may only be dereferenced
 227  * if either the RCU read lock is held, or that the lock required to replace
 228  * the bar struct at foo->bar is held.
 229  *
 230  * Note that the list of conditions may also include indications of when a lock
 231  * need not be held, for example during initialisation or destruction of the
 232  * target struct:
 233  *
 234  *      bar = rcu_dereference_check(foo->bar, rcu_read_lock_held() ||
 235  *                                            lockdep_is_held(&foo->lock) ||
 236  *                                            atomic_read(&foo->usage) == 0);
 237  */
 238 #define rcu_dereference_check(p, c) \
 239         ({ \
 240                 __do_rcu_dereference_check(c); \
 241                 rcu_dereference_raw(p); \
 242         })
 243
 244 /**
 245  * rcu_dereference_protected - fetch RCU pointer when updates prevented
 246  *
 247  * Return the value of the specified RCU-protected pointer, but omit
 248  * both the smp_read_barrier_depends() and the ACCESS_ONCE().  This
 249  * is useful in cases where update-side locks prevent the value of the
 250  * pointer from changing.  Please note that this primitive does -not-
 251  * prevent the compiler from repeating this reference or combining it
 252  * with other references, so it should not be used without protection
 253  * of appropriate locks.
 254  */
 255 #define rcu_dereference_protected(p, c) \
 256         ({ \
 257                 __do_rcu_dereference_check(c); \
 258                 (p); \
 259         })
 260
 261 #else /* #ifdef CONFIG_PROVE_RCU */
 262
 263 #define rcu_dereference_check(p, c)     rcu_dereference_raw(p)
 264 #define rcu_dereference_protected(p, c) (p)
 265
 266 #endif /* #else #ifdef CONFIG_PROVE_RCU */
 267
 268 /**
 269  * rcu_access_pointer - fetch RCU pointer with no dereferencing
 270  *
 271  * Return the value of the specified RCU-protected pointer, but omit the
 272  * smp_read_barrier_depends() and keep the ACCESS_ONCE().  This is useful
 273  * when the value of this pointer is accessed, but the pointer is not
 274  * dereferenced, for example, when testing an RCU-protected pointer against
 275  * NULL.  This may also be used in cases where update-side locks prevent
 276  * the value of the pointer from changing, but rcu_dereference_protected()
 277  * is a lighter-weight primitive for this use case.
 278  */
 279 #define rcu_access_pointer(p)   ACCESS_ONCE(p)
 280
 281 /**
 282  * rcu_read_lock - mark the beginning of an RCU read-side critical section.
 283  *
 284  * When synchronize_rcu() is invoked on one CPU while other CPUs
 285  * are within RCU read-side critical sections, then the
 286  * synchronize_rcu() is guaranteed to block until after all the other
 287  * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
 288  * on one CPU while other CPUs are within RCU read-side critical
 289  * sections, invocation of the corresponding RCU callback is deferred
 290  * until after the all the other CPUs exit their critical sections.
 291  *
 292  * Note, however, that RCU callbacks are permitted to run concurrently
 293  * with RCU read-side critical sections.  One way that this can happen
 294  * is via the following sequence of events: (1) CPU 0 enters an RCU
 295  * read-side critical section, (2) CPU 1 invokes call_rcu() to register
 296  * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
 297  * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
 298  * callback is invoked.  This is legal, because the RCU read-side critical
 299  * section that was running concurrently with the call_rcu() (and which
 300  * therefore might be referencing something that the corresponding RCU
 301  * callback would free up) has completed before the corresponding
 302  * RCU callback is invoked.
 303  *
 304  * RCU read-side critical sections may be nested.  Any deferred actions
 305  * will be deferred until the outermost RCU read-side critical section
 306  * completes.
 307  *
 308  * It is illegal to block while in an RCU read-side critical section.
 309  */
 310 static inline void rcu_read_lock(void)
 311 {
 312         __rcu_read_lock();
 313         __acquire(RCU);
 314         rcu_read_acquire();
 315 }
 316
 317 /*
 318  * So where is rcu_write_lock()?  It does not exist, as there is no
 319  * way for writers to lock out RCU readers.  This is a feature, not
 320  * a bug -- this property is what provides RCU's performance benefits.
 321  * Of course, writers must coordinate with each other.  The normal
 322  * spinlock primitives work well for this, but any other technique may be
 323  * used as well.  RCU does not care how the writers keep out of each
 324  * others' way, as long as they do so.
 325  */
 326
 327 /**
 328  * rcu_read_unlock - marks the end of an RCU read-side critical section.
 329  *
 330  * See rcu_read_lock() for more information.
 331  */
 332 static inline void rcu_read_unlock(void)
 333 {
 334         rcu_read_release();
 335         __release(RCU);
 336         __rcu_read_unlock();
 337 }
 338
 339 /**
 340  * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
 341  *
 342  * This is equivalent of rcu_read_lock(), but to be used when updates
 343  * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
 344  * consider completion of a softirq handler to be a quiescent state,
 345  * a process in RCU read-side critical section must be protected by
 346  * disabling softirqs. Read-side critical sections in interrupt context
 347  * can use just rcu_read_lock().
 348  *
 349  */
 350 static inline void rcu_read_lock_bh(void)
 351 {
 352         __rcu_read_lock_bh();
 353         __acquire(RCU_BH);
 354         rcu_read_acquire_bh();
 355 }
 356
 357 /*
 358  * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
 359  *
 360  * See rcu_read_lock_bh() for more information.
 361  */
 362 static inline void rcu_read_unlock_bh(void)
 363 {
 364         rcu_read_release_bh();
 365         __release(RCU_BH);
 366         __rcu_read_unlock_bh();
 367 }
 368
 369 /**
 370  * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
 371  *
 372  * Should be used with either
 373  * - synchronize_sched()
 374  * or
 375  * - call_rcu_sched() and rcu_barrier_sched()
 376  * on the write-side to insure proper synchronization.
 377  */
 378 static inline void rcu_read_lock_sched(void)
 379 {
 380         preempt_disable();
 381         __acquire(RCU_SCHED);
 382         rcu_read_acquire_sched();
 383 }
 384
 385 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
 386 static inline notrace void rcu_read_lock_sched_notrace(void)
 387 {
 388         preempt_disable_notrace();
 389         __acquire(RCU_SCHED);
 390 }
 391
 392 /*
 393  * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
 394  *
 395  * See rcu_read_lock_sched for more information.
 396  */
 397 static inline void rcu_read_unlock_sched(void)
 398 {
 399         rcu_read_release_sched();
 400         __release(RCU_SCHED);
 401         preempt_enable();
 402 }
 403
 404 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
 405 static inline notrace void rcu_read_unlock_sched_notrace(void)
 406 {
 407         __release(RCU_SCHED);
 408         preempt_enable_notrace();
 409 }
 410
 411
 412 /**
 413  * rcu_dereference_raw - fetch an RCU-protected pointer
 414  *
 415  * The caller must be within some flavor of RCU read-side critical
 416  * section, or must be otherwise preventing the pointer from changing,
 417  * for example, by holding an appropriate lock.  This pointer may later
 418  * be safely dereferenced.  It is the caller's responsibility to have
 419  * done the right thing, as this primitive does no checking of any kind.
 420  *
 421  * Inserts memory barriers on architectures that require them
 422  * (currently only the Alpha), and, more importantly, documents
 423  * exactly which pointers are protected by RCU.
 424  */
 425 #define rcu_dereference_raw(p)  ({ \
 426                                 typeof(p) _________p1 = ACCESS_ONCE(p); \
 427                                 smp_read_barrier_depends(); \
 428                                 (_________p1); \
 429                                 })
 430
 431 /**
 432  * rcu_dereference - fetch an RCU-protected pointer, checking for RCU
 433  *
 434  * Makes rcu_dereference_check() do the dirty work.
 435  */
 436 #define rcu_dereference(p) \
 437         rcu_dereference_check(p, rcu_read_lock_held())
 438
 439 /**
 440  * rcu_dereference_bh - fetch an RCU-protected pointer, checking for RCU-bh
 441  *
 442  * Makes rcu_dereference_check() do the dirty work.
 443  */
 444 #define rcu_dereference_bh(p) \
 445                 rcu_dereference_check(p, rcu_read_lock_bh_held())
 446
 447 /**
 448  * rcu_dereference_sched - fetch RCU-protected pointer, checking for RCU-sched
 449  *
 450  * Makes rcu_dereference_check() do the dirty work.
 451  */
 452 #define rcu_dereference_sched(p) \
 453                 rcu_dereference_check(p, rcu_read_lock_sched_held())
 454
 455 /**
 456  * rcu_assign_pointer - assign (publicize) a pointer to a newly
 457  * initialized structure that will be dereferenced by RCU read-side
 458  * critical sections.  Returns the value assigned.
 459  *
 460  * Inserts memory barriers on architectures that require them
 461  * (pretty much all of them other than x86), and also prevents
 462  * the compiler from reordering the code that initializes the
 463  * structure after the pointer assignment.  More importantly, this
 464  * call documents which pointers will be dereferenced by RCU read-side
 465  * code.
 466  */
 467
 468 #define rcu_assign_pointer(p, v) \
 469         ({ \
 470                 if (!__builtin_constant_p(v) || \
 471                     ((v) != NULL)) \
 472                         smp_wmb(); \
 473                 (p) = (v); \
 474         })
 475
 476 /* Infrastructure to implement the synchronize_() primitives. */
 477
 478 struct rcu_synchronize {
 479         struct rcu_head head;
 480         struct completion completion;
 481 };
 482
 483 extern void wakeme_after_rcu(struct rcu_head  *head);
 484
 485 /**
 486  * call_rcu - Queue an RCU callback for invocation after a grace period.
 487  * @head: structure to be used for queueing the RCU updates.
 488  * @func: actual update function to be invoked after the grace period
 489  *
 490  * The update function will be invoked some time after a full grace
 491  * period elapses, in other words after all currently executing RCU
 492  * read-side critical sections have completed.  RCU read-side critical
 493  * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
 494  * and may be nested.
 495  */
 496 extern void call_rcu(struct rcu_head *head,
 497                               void (*func)(struct rcu_head *head));
 498
 499 /**
 500  * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
 501  * @head: structure to be used for queueing the RCU updates.
 502  * @func: actual update function to be invoked after the grace period
 503  *
 504  * The update function will be invoked some time after a full grace
 505  * period elapses, in other words after all currently executing RCU
 506  * read-side critical sections have completed. call_rcu_bh() assumes
 507  * that the read-side critical sections end on completion of a softirq
 508  * handler. This means that read-side critical sections in process
 509  * context must not be interrupted by softirqs. This interface is to be
 510  * used when most of the read-side critical sections are in softirq context.
 511  * RCU read-side critical sections are delimited by :
 512  *  - rcu_read_lock() and  rcu_read_unlock(), if in interrupt context.
 513  *  OR
 514  *  - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
 515  *  These may be nested.
 516  */
 517 extern void call_rcu_bh(struct rcu_head *head,
 518                         void (*func)(struct rcu_head *head));
 519
 520 #endif /* __LINUX_RCUPDATE_H */