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