linux/include/linux/rcupdate.h
<<
>>
Prefs
   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/types.h>
  37#include <linux/cache.h>
  38#include <linux/spinlock.h>
  39#include <linux/threads.h>
  40#include <linux/cpumask.h>
  41#include <linux/seqlock.h>
  42#include <linux/lockdep.h>
  43#include <linux/completion.h>
  44#include <linux/debugobjects.h>
  45#include <linux/bug.h>
  46#include <linux/compiler.h>
  47
  48#ifdef CONFIG_RCU_TORTURE_TEST
  49extern int rcutorture_runnable; /* for sysctl */
  50#endif /* #ifdef CONFIG_RCU_TORTURE_TEST */
  51
  52#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
  53extern void rcutorture_record_test_transition(void);
  54extern void rcutorture_record_progress(unsigned long vernum);
  55extern void do_trace_rcu_torture_read(char *rcutorturename,
  56                                      struct rcu_head *rhp);
  57#else
  58static inline void rcutorture_record_test_transition(void)
  59{
  60}
  61static inline void rcutorture_record_progress(unsigned long vernum)
  62{
  63}
  64#ifdef CONFIG_RCU_TRACE
  65extern void do_trace_rcu_torture_read(char *rcutorturename,
  66                                      struct rcu_head *rhp);
  67#else
  68#define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
  69#endif
  70#endif
  71
  72#define UINT_CMP_GE(a, b)       (UINT_MAX / 2 >= (a) - (b))
  73#define UINT_CMP_LT(a, b)       (UINT_MAX / 2 < (a) - (b))
  74#define ULONG_CMP_GE(a, b)      (ULONG_MAX / 2 >= (a) - (b))
  75#define ULONG_CMP_LT(a, b)      (ULONG_MAX / 2 < (a) - (b))
  76
  77/* Exported common interfaces */
  78
  79#ifdef CONFIG_PREEMPT_RCU
  80
  81/**
  82 * call_rcu() - Queue an RCU callback for invocation after a grace period.
  83 * @head: structure to be used for queueing the RCU updates.
  84 * @func: actual callback function to be invoked after the grace period
  85 *
  86 * The callback function will be invoked some time after a full grace
  87 * period elapses, in other words after all pre-existing RCU read-side
  88 * critical sections have completed.  However, the callback function
  89 * might well execute concurrently with RCU read-side critical sections
  90 * that started after call_rcu() was invoked.  RCU read-side critical
  91 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
  92 * and may be nested.
  93 */
  94extern void call_rcu(struct rcu_head *head,
  95                              void (*func)(struct rcu_head *head));
  96
  97#else /* #ifdef CONFIG_PREEMPT_RCU */
  98
  99/* In classic RCU, call_rcu() is just call_rcu_sched(). */
 100#define call_rcu        call_rcu_sched
 101
 102#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
 103
 104/**
 105 * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
 106 * @head: structure to be used for queueing the RCU updates.
 107 * @func: actual callback function to be invoked after the grace period
 108 *
 109 * The callback function will be invoked some time after a full grace
 110 * period elapses, in other words after all currently executing RCU
 111 * read-side critical sections have completed. call_rcu_bh() assumes
 112 * that the read-side critical sections end on completion of a softirq
 113 * handler. This means that read-side critical sections in process
 114 * context must not be interrupted by softirqs. This interface is to be
 115 * used when most of the read-side critical sections are in softirq context.
 116 * RCU read-side critical sections are delimited by :
 117 *  - rcu_read_lock() and  rcu_read_unlock(), if in interrupt context.
 118 *  OR
 119 *  - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
 120 *  These may be nested.
 121 */
 122extern void call_rcu_bh(struct rcu_head *head,
 123                        void (*func)(struct rcu_head *head));
 124
 125/**
 126 * call_rcu_sched() - Queue an RCU for invocation after sched grace period.
 127 * @head: structure to be used for queueing the RCU updates.
 128 * @func: actual callback function to be invoked after the grace period
 129 *
 130 * The callback function will be invoked some time after a full grace
 131 * period elapses, in other words after all currently executing RCU
 132 * read-side critical sections have completed. call_rcu_sched() assumes
 133 * that the read-side critical sections end on enabling of preemption
 134 * or on voluntary preemption.
 135 * RCU read-side critical sections are delimited by :
 136 *  - rcu_read_lock_sched() and  rcu_read_unlock_sched(),
 137 *  OR
 138 *  anything that disables preemption.
 139 *  These may be nested.
 140 */
 141extern void call_rcu_sched(struct rcu_head *head,
 142                           void (*func)(struct rcu_head *rcu));
 143
 144extern void synchronize_sched(void);
 145
 146#ifdef CONFIG_PREEMPT_RCU
 147
 148extern void __rcu_read_lock(void);
 149extern void __rcu_read_unlock(void);
 150extern void rcu_read_unlock_special(struct task_struct *t);
 151void synchronize_rcu(void);
 152
 153/*
 154 * Defined as a macro as it is a very low level header included from
 155 * areas that don't even know about current.  This gives the rcu_read_lock()
 156 * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
 157 * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
 158 */
 159#define rcu_preempt_depth() (current->rcu_read_lock_nesting)
 160
 161#else /* #ifdef CONFIG_PREEMPT_RCU */
 162
 163static inline void __rcu_read_lock(void)
 164{
 165        preempt_disable();
 166}
 167
 168static inline void __rcu_read_unlock(void)
 169{
 170        preempt_enable();
 171}
 172
 173static inline void synchronize_rcu(void)
 174{
 175        synchronize_sched();
 176}
 177
 178static inline int rcu_preempt_depth(void)
 179{
 180        return 0;
 181}
 182
 183#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
 184
 185/* Internal to kernel */
 186extern void rcu_sched_qs(int cpu);
 187extern void rcu_bh_qs(int cpu);
 188extern void rcu_check_callbacks(int cpu, int user);
 189struct notifier_block;
 190extern void rcu_idle_enter(void);
 191extern void rcu_idle_exit(void);
 192extern void rcu_irq_enter(void);
 193extern void rcu_irq_exit(void);
 194
 195#ifdef CONFIG_RCU_USER_QS
 196extern void rcu_user_enter(void);
 197extern void rcu_user_exit(void);
 198extern void rcu_user_enter_after_irq(void);
 199extern void rcu_user_exit_after_irq(void);
 200extern void rcu_user_hooks_switch(struct task_struct *prev,
 201                                  struct task_struct *next);
 202#else
 203static inline void rcu_user_enter(void) { }
 204static inline void rcu_user_exit(void) { }
 205static inline void rcu_user_enter_after_irq(void) { }
 206static inline void rcu_user_exit_after_irq(void) { }
 207#endif /* CONFIG_RCU_USER_QS */
 208
 209extern void exit_rcu(void);
 210
 211/**
 212 * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
 213 * @a: Code that RCU needs to pay attention to.
 214 *
 215 * RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden
 216 * in the inner idle loop, that is, between the rcu_idle_enter() and
 217 * the rcu_idle_exit() -- RCU will happily ignore any such read-side
 218 * critical sections.  However, things like powertop need tracepoints
 219 * in the inner idle loop.
 220 *
 221 * This macro provides the way out:  RCU_NONIDLE(do_something_with_RCU())
 222 * will tell RCU that it needs to pay attending, invoke its argument
 223 * (in this example, a call to the do_something_with_RCU() function),
 224 * and then tell RCU to go back to ignoring this CPU.  It is permissible
 225 * to nest RCU_NONIDLE() wrappers, but the nesting level is currently
 226 * quite limited.  If deeper nesting is required, it will be necessary
 227 * to adjust DYNTICK_TASK_NESTING_VALUE accordingly.
 228 */
 229#define RCU_NONIDLE(a) \
 230        do { \
 231                rcu_irq_enter(); \
 232                do { a; } while (0); \
 233                rcu_irq_exit(); \
 234        } while (0)
 235
 236/*
 237 * Infrastructure to implement the synchronize_() primitives in
 238 * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
 239 */
 240
 241typedef void call_rcu_func_t(struct rcu_head *head,
 242                             void (*func)(struct rcu_head *head));
 243void wait_rcu_gp(call_rcu_func_t crf);
 244
 245#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
 246#include <linux/rcutree.h>
 247#elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU)
 248#include <linux/rcutiny.h>
 249#else
 250#error "Unknown RCU implementation specified to kernel configuration"
 251#endif
 252
 253/*
 254 * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic
 255 * initialization and destruction of rcu_head on the stack. rcu_head structures
 256 * allocated dynamically in the heap or defined statically don't need any
 257 * initialization.
 258 */
 259#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
 260extern void init_rcu_head_on_stack(struct rcu_head *head);
 261extern void destroy_rcu_head_on_stack(struct rcu_head *head);
 262#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
 263static inline void init_rcu_head_on_stack(struct rcu_head *head)
 264{
 265}
 266
 267static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
 268{
 269}
 270#endif  /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
 271
 272#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SMP)
 273extern int rcu_is_cpu_idle(void);
 274#endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SMP) */
 275
 276#if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
 277bool rcu_lockdep_current_cpu_online(void);
 278#else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
 279static inline bool rcu_lockdep_current_cpu_online(void)
 280{
 281        return 1;
 282}
 283#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
 284
 285#ifdef CONFIG_DEBUG_LOCK_ALLOC
 286
 287static inline void rcu_lock_acquire(struct lockdep_map *map)
 288{
 289        lock_acquire(map, 0, 0, 2, 1, NULL, _THIS_IP_);
 290}
 291
 292static inline void rcu_lock_release(struct lockdep_map *map)
 293{
 294        lock_release(map, 1, _THIS_IP_);
 295}
 296
 297extern struct lockdep_map rcu_lock_map;
 298extern struct lockdep_map rcu_bh_lock_map;
 299extern struct lockdep_map rcu_sched_lock_map;
 300extern int debug_lockdep_rcu_enabled(void);
 301
 302/**
 303 * rcu_read_lock_held() - might we be in RCU read-side critical section?
 304 *
 305 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
 306 * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
 307 * this assumes we are in an RCU read-side critical section unless it can
 308 * prove otherwise.  This is useful for debug checks in functions that
 309 * require that they be called within an RCU read-side critical section.
 310 *
 311 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
 312 * and while lockdep is disabled.
 313 *
 314 * Note that rcu_read_lock() and the matching rcu_read_unlock() must
 315 * occur in the same context, for example, it is illegal to invoke
 316 * rcu_read_unlock() in process context if the matching rcu_read_lock()
 317 * was invoked from within an irq handler.
 318 *
 319 * Note that rcu_read_lock() is disallowed if the CPU is either idle or
 320 * offline from an RCU perspective, so check for those as well.
 321 */
 322static inline int rcu_read_lock_held(void)
 323{
 324        if (!debug_lockdep_rcu_enabled())
 325                return 1;
 326        if (rcu_is_cpu_idle())
 327                return 0;
 328        if (!rcu_lockdep_current_cpu_online())
 329                return 0;
 330        return lock_is_held(&rcu_lock_map);
 331}
 332
 333/*
 334 * rcu_read_lock_bh_held() is defined out of line to avoid #include-file
 335 * hell.
 336 */
 337extern int rcu_read_lock_bh_held(void);
 338
 339/**
 340 * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
 341 *
 342 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
 343 * RCU-sched read-side critical section.  In absence of
 344 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
 345 * critical section unless it can prove otherwise.  Note that disabling
 346 * of preemption (including disabling irqs) counts as an RCU-sched
 347 * read-side critical section.  This is useful for debug checks in functions
 348 * that required that they be called within an RCU-sched read-side
 349 * critical section.
 350 *
 351 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
 352 * and while lockdep is disabled.
 353 *
 354 * Note that if the CPU is in the idle loop from an RCU point of
 355 * view (ie: that we are in the section between rcu_idle_enter() and
 356 * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
 357 * did an rcu_read_lock().  The reason for this is that RCU ignores CPUs
 358 * that are in such a section, considering these as in extended quiescent
 359 * state, so such a CPU is effectively never in an RCU read-side critical
 360 * section regardless of what RCU primitives it invokes.  This state of
 361 * affairs is required --- we need to keep an RCU-free window in idle
 362 * where the CPU may possibly enter into low power mode. This way we can
 363 * notice an extended quiescent state to other CPUs that started a grace
 364 * period. Otherwise we would delay any grace period as long as we run in
 365 * the idle task.
 366 *
 367 * Similarly, we avoid claiming an SRCU read lock held if the current
 368 * CPU is offline.
 369 */
 370#ifdef CONFIG_PREEMPT_COUNT
 371static inline int rcu_read_lock_sched_held(void)
 372{
 373        int lockdep_opinion = 0;
 374
 375        if (!debug_lockdep_rcu_enabled())
 376                return 1;
 377        if (rcu_is_cpu_idle())
 378                return 0;
 379        if (!rcu_lockdep_current_cpu_online())
 380                return 0;
 381        if (debug_locks)
 382                lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
 383        return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
 384}
 385#else /* #ifdef CONFIG_PREEMPT_COUNT */
 386static inline int rcu_read_lock_sched_held(void)
 387{
 388        return 1;
 389}
 390#endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
 391
 392#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 393
 394# define rcu_lock_acquire(a)            do { } while (0)
 395# define rcu_lock_release(a)            do { } while (0)
 396
 397static inline int rcu_read_lock_held(void)
 398{
 399        return 1;
 400}
 401
 402static inline int rcu_read_lock_bh_held(void)
 403{
 404        return 1;
 405}
 406
 407#ifdef CONFIG_PREEMPT_COUNT
 408static inline int rcu_read_lock_sched_held(void)
 409{
 410        return preempt_count() != 0 || irqs_disabled();
 411}
 412#else /* #ifdef CONFIG_PREEMPT_COUNT */
 413static inline int rcu_read_lock_sched_held(void)
 414{
 415        return 1;
 416}
 417#endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
 418
 419#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 420
 421#ifdef CONFIG_PROVE_RCU
 422
 423extern int rcu_my_thread_group_empty(void);
 424
 425/**
 426 * rcu_lockdep_assert - emit lockdep splat if specified condition not met
 427 * @c: condition to check
 428 * @s: informative message
 429 */
 430#define rcu_lockdep_assert(c, s)                                        \
 431        do {                                                            \
 432                static bool __section(.data.unlikely) __warned;         \
 433                if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
 434                        __warned = true;                                \
 435                        lockdep_rcu_suspicious(__FILE__, __LINE__, s);  \
 436                }                                                       \
 437        } while (0)
 438
 439#if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
 440static inline void rcu_preempt_sleep_check(void)
 441{
 442        rcu_lockdep_assert(!lock_is_held(&rcu_lock_map),
 443                           "Illegal context switch in RCU read-side critical section");
 444}
 445#else /* #ifdef CONFIG_PROVE_RCU */
 446static inline void rcu_preempt_sleep_check(void)
 447{
 448}
 449#endif /* #else #ifdef CONFIG_PROVE_RCU */
 450
 451#define rcu_sleep_check()                                               \
 452        do {                                                            \
 453                rcu_preempt_sleep_check();                              \
 454                rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map),     \
 455                                   "Illegal context switch in RCU-bh"   \
 456                                   " read-side critical section");      \
 457                rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map),  \
 458                                   "Illegal context switch in RCU-sched"\
 459                                   " read-side critical section");      \
 460        } while (0)
 461
 462#else /* #ifdef CONFIG_PROVE_RCU */
 463
 464#define rcu_lockdep_assert(c, s) do { } while (0)
 465#define rcu_sleep_check() do { } while (0)
 466
 467#endif /* #else #ifdef CONFIG_PROVE_RCU */
 468
 469/*
 470 * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
 471 * and rcu_assign_pointer().  Some of these could be folded into their
 472 * callers, but they are left separate in order to ease introduction of
 473 * multiple flavors of pointers to match the multiple flavors of RCU
 474 * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in
 475 * the future.
 476 */
 477
 478#ifdef __CHECKER__
 479#define rcu_dereference_sparse(p, space) \
 480        ((void)(((typeof(*p) space *)p) == p))
 481#else /* #ifdef __CHECKER__ */
 482#define rcu_dereference_sparse(p, space)
 483#endif /* #else #ifdef __CHECKER__ */
 484
 485#define __rcu_access_pointer(p, space) \
 486        ({ \
 487                typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
 488                rcu_dereference_sparse(p, space); \
 489                ((typeof(*p) __force __kernel *)(_________p1)); \
 490        })
 491#define __rcu_dereference_check(p, c, space) \
 492        ({ \
 493                typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
 494                rcu_lockdep_assert(c, "suspicious rcu_dereference_check()" \
 495                                      " usage"); \
 496                rcu_dereference_sparse(p, space); \
 497                smp_read_barrier_depends(); \
 498                ((typeof(*p) __force __kernel *)(_________p1)); \
 499        })
 500#define __rcu_dereference_protected(p, c, space) \
 501        ({ \
 502                rcu_lockdep_assert(c, "suspicious rcu_dereference_protected()" \
 503                                      " usage"); \
 504                rcu_dereference_sparse(p, space); \
 505                ((typeof(*p) __force __kernel *)(p)); \
 506        })
 507
 508#define __rcu_access_index(p, space) \
 509        ({ \
 510                typeof(p) _________p1 = ACCESS_ONCE(p); \
 511                rcu_dereference_sparse(p, space); \
 512                (_________p1); \
 513        })
 514#define __rcu_dereference_index_check(p, c) \
 515        ({ \
 516                typeof(p) _________p1 = ACCESS_ONCE(p); \
 517                rcu_lockdep_assert(c, \
 518                                   "suspicious rcu_dereference_index_check()" \
 519                                   " usage"); \
 520                smp_read_barrier_depends(); \
 521                (_________p1); \
 522        })
 523#define __rcu_assign_pointer(p, v, space) \
 524        do { \
 525                smp_wmb(); \
 526                (p) = (typeof(*v) __force space *)(v); \
 527        } while (0)
 528
 529
 530/**
 531 * rcu_access_pointer() - fetch RCU pointer with no dereferencing
 532 * @p: The pointer to read
 533 *
 534 * Return the value of the specified RCU-protected pointer, but omit the
 535 * smp_read_barrier_depends() and keep the ACCESS_ONCE().  This is useful
 536 * when the value of this pointer is accessed, but the pointer is not
 537 * dereferenced, for example, when testing an RCU-protected pointer against
 538 * NULL.  Although rcu_access_pointer() may also be used in cases where
 539 * update-side locks prevent the value of the pointer from changing, you
 540 * should instead use rcu_dereference_protected() for this use case.
 541 *
 542 * It is also permissible to use rcu_access_pointer() when read-side
 543 * access to the pointer was removed at least one grace period ago, as
 544 * is the case in the context of the RCU callback that is freeing up
 545 * the data, or after a synchronize_rcu() returns.  This can be useful
 546 * when tearing down multi-linked structures after a grace period
 547 * has elapsed.
 548 */
 549#define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
 550
 551/**
 552 * rcu_dereference_check() - rcu_dereference with debug checking
 553 * @p: The pointer to read, prior to dereferencing
 554 * @c: The conditions under which the dereference will take place
 555 *
 556 * Do an rcu_dereference(), but check that the conditions under which the
 557 * dereference will take place are correct.  Typically the conditions
 558 * indicate the various locking conditions that should be held at that
 559 * point.  The check should return true if the conditions are satisfied.
 560 * An implicit check for being in an RCU read-side critical section
 561 * (rcu_read_lock()) is included.
 562 *
 563 * For example:
 564 *
 565 *      bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
 566 *
 567 * could be used to indicate to lockdep that foo->bar may only be dereferenced
 568 * if either rcu_read_lock() is held, or that the lock required to replace
 569 * the bar struct at foo->bar is held.
 570 *
 571 * Note that the list of conditions may also include indications of when a lock
 572 * need not be held, for example during initialisation or destruction of the
 573 * target struct:
 574 *
 575 *      bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
 576 *                                            atomic_read(&foo->usage) == 0);
 577 *
 578 * Inserts memory barriers on architectures that require them
 579 * (currently only the Alpha), prevents the compiler from refetching
 580 * (and from merging fetches), and, more importantly, documents exactly
 581 * which pointers are protected by RCU and checks that the pointer is
 582 * annotated as __rcu.
 583 */
 584#define rcu_dereference_check(p, c) \
 585        __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)
 586
 587/**
 588 * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
 589 * @p: The pointer to read, prior to dereferencing
 590 * @c: The conditions under which the dereference will take place
 591 *
 592 * This is the RCU-bh counterpart to rcu_dereference_check().
 593 */
 594#define rcu_dereference_bh_check(p, c) \
 595        __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu)
 596
 597/**
 598 * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
 599 * @p: The pointer to read, prior to dereferencing
 600 * @c: The conditions under which the dereference will take place
 601 *
 602 * This is the RCU-sched counterpart to rcu_dereference_check().
 603 */
 604#define rcu_dereference_sched_check(p, c) \
 605        __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \
 606                                __rcu)
 607
 608#define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/
 609
 610/**
 611 * rcu_access_index() - fetch RCU index with no dereferencing
 612 * @p: The index to read
 613 *
 614 * Return the value of the specified RCU-protected index, but omit the
 615 * smp_read_barrier_depends() and keep the ACCESS_ONCE().  This is useful
 616 * when the value of this index is accessed, but the index is not
 617 * dereferenced, for example, when testing an RCU-protected index against
 618 * -1.  Although rcu_access_index() may also be used in cases where
 619 * update-side locks prevent the value of the index from changing, you
 620 * should instead use rcu_dereference_index_protected() for this use case.
 621 */
 622#define rcu_access_index(p) __rcu_access_index((p), __rcu)
 623
 624/**
 625 * rcu_dereference_index_check() - rcu_dereference for indices with debug checking
 626 * @p: The pointer to read, prior to dereferencing
 627 * @c: The conditions under which the dereference will take place
 628 *
 629 * Similar to rcu_dereference_check(), but omits the sparse checking.
 630 * This allows rcu_dereference_index_check() to be used on integers,
 631 * which can then be used as array indices.  Attempting to use
 632 * rcu_dereference_check() on an integer will give compiler warnings
 633 * because the sparse address-space mechanism relies on dereferencing
 634 * the RCU-protected pointer.  Dereferencing integers is not something
 635 * that even gcc will put up with.
 636 *
 637 * Note that this function does not implicitly check for RCU read-side
 638 * critical sections.  If this function gains lots of uses, it might
 639 * make sense to provide versions for each flavor of RCU, but it does
 640 * not make sense as of early 2010.
 641 */
 642#define rcu_dereference_index_check(p, c) \
 643        __rcu_dereference_index_check((p), (c))
 644
 645/**
 646 * rcu_dereference_protected() - fetch RCU pointer when updates prevented
 647 * @p: The pointer to read, prior to dereferencing
 648 * @c: The conditions under which the dereference will take place
 649 *
 650 * Return the value of the specified RCU-protected pointer, but omit
 651 * both the smp_read_barrier_depends() and the ACCESS_ONCE().  This
 652 * is useful in cases where update-side locks prevent the value of the
 653 * pointer from changing.  Please note that this primitive does -not-
 654 * prevent the compiler from repeating this reference or combining it
 655 * with other references, so it should not be used without protection
 656 * of appropriate locks.
 657 *
 658 * This function is only for update-side use.  Using this function
 659 * when protected only by rcu_read_lock() will result in infrequent
 660 * but very ugly failures.
 661 */
 662#define rcu_dereference_protected(p, c) \
 663        __rcu_dereference_protected((p), (c), __rcu)
 664
 665
 666/**
 667 * rcu_dereference() - fetch RCU-protected pointer for dereferencing
 668 * @p: The pointer to read, prior to dereferencing
 669 *
 670 * This is a simple wrapper around rcu_dereference_check().
 671 */
 672#define rcu_dereference(p) rcu_dereference_check(p, 0)
 673
 674/**
 675 * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
 676 * @p: The pointer to read, prior to dereferencing
 677 *
 678 * Makes rcu_dereference_check() do the dirty work.
 679 */
 680#define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
 681
 682/**
 683 * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
 684 * @p: The pointer to read, prior to dereferencing
 685 *
 686 * Makes rcu_dereference_check() do the dirty work.
 687 */
 688#define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
 689
 690/**
 691 * rcu_read_lock() - mark the beginning of an RCU read-side critical section
 692 *
 693 * When synchronize_rcu() is invoked on one CPU while other CPUs
 694 * are within RCU read-side critical sections, then the
 695 * synchronize_rcu() is guaranteed to block until after all the other
 696 * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
 697 * on one CPU while other CPUs are within RCU read-side critical
 698 * sections, invocation of the corresponding RCU callback is deferred
 699 * until after the all the other CPUs exit their critical sections.
 700 *
 701 * Note, however, that RCU callbacks are permitted to run concurrently
 702 * with new RCU read-side critical sections.  One way that this can happen
 703 * is via the following sequence of events: (1) CPU 0 enters an RCU
 704 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
 705 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
 706 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
 707 * callback is invoked.  This is legal, because the RCU read-side critical
 708 * section that was running concurrently with the call_rcu() (and which
 709 * therefore might be referencing something that the corresponding RCU
 710 * callback would free up) has completed before the corresponding
 711 * RCU callback is invoked.
 712 *
 713 * RCU read-side critical sections may be nested.  Any deferred actions
 714 * will be deferred until the outermost RCU read-side critical section
 715 * completes.
 716 *
 717 * You can avoid reading and understanding the next paragraph by
 718 * following this rule: don't put anything in an rcu_read_lock() RCU
 719 * read-side critical section that would block in a !PREEMPT kernel.
 720 * But if you want the full story, read on!
 721 *
 722 * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it
 723 * is illegal to block while in an RCU read-side critical section.  In
 724 * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU)
 725 * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may
 726 * be preempted, but explicit blocking is illegal.  Finally, in preemptible
 727 * RCU implementations in real-time (CONFIG_PREEMPT_RT) kernel builds,
 728 * RCU read-side critical sections may be preempted and they may also
 729 * block, but only when acquiring spinlocks that are subject to priority
 730 * inheritance.
 731 */
 732static inline void rcu_read_lock(void)
 733{
 734        __rcu_read_lock();
 735        __acquire(RCU);
 736        rcu_lock_acquire(&rcu_lock_map);
 737        rcu_lockdep_assert(!rcu_is_cpu_idle(),
 738                           "rcu_read_lock() used illegally while idle");
 739}
 740
 741/*
 742 * So where is rcu_write_lock()?  It does not exist, as there is no
 743 * way for writers to lock out RCU readers.  This is a feature, not
 744 * a bug -- this property is what provides RCU's performance benefits.
 745 * Of course, writers must coordinate with each other.  The normal
 746 * spinlock primitives work well for this, but any other technique may be
 747 * used as well.  RCU does not care how the writers keep out of each
 748 * others' way, as long as they do so.
 749 */
 750
 751/**
 752 * rcu_read_unlock() - marks the end of an RCU read-side critical section.
 753 *
 754 * See rcu_read_lock() for more information.
 755 */
 756static inline void rcu_read_unlock(void)
 757{
 758        rcu_lockdep_assert(!rcu_is_cpu_idle(),
 759                           "rcu_read_unlock() used illegally while idle");
 760        rcu_lock_release(&rcu_lock_map);
 761        __release(RCU);
 762        __rcu_read_unlock();
 763}
 764
 765/**
 766 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
 767 *
 768 * This is equivalent of rcu_read_lock(), but to be used when updates
 769 * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since
 770 * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a
 771 * softirq handler to be a quiescent state, a process in RCU read-side
 772 * critical section must be protected by disabling softirqs. Read-side
 773 * critical sections in interrupt context can use just rcu_read_lock(),
 774 * though this should at least be commented to avoid confusing people
 775 * reading the code.
 776 *
 777 * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
 778 * must occur in the same context, for example, it is illegal to invoke
 779 * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
 780 * was invoked from some other task.
 781 */
 782static inline void rcu_read_lock_bh(void)
 783{
 784        local_bh_disable();
 785        __acquire(RCU_BH);
 786        rcu_lock_acquire(&rcu_bh_lock_map);
 787        rcu_lockdep_assert(!rcu_is_cpu_idle(),
 788                           "rcu_read_lock_bh() used illegally while idle");
 789}
 790
 791/*
 792 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
 793 *
 794 * See rcu_read_lock_bh() for more information.
 795 */
 796static inline void rcu_read_unlock_bh(void)
 797{
 798        rcu_lockdep_assert(!rcu_is_cpu_idle(),
 799                           "rcu_read_unlock_bh() used illegally while idle");
 800        rcu_lock_release(&rcu_bh_lock_map);
 801        __release(RCU_BH);
 802        local_bh_enable();
 803}
 804
 805/**
 806 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
 807 *
 808 * This is equivalent of rcu_read_lock(), but to be used when updates
 809 * are being done using call_rcu_sched() or synchronize_rcu_sched().
 810 * Read-side critical sections can also be introduced by anything that
 811 * disables preemption, including local_irq_disable() and friends.
 812 *
 813 * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
 814 * must occur in the same context, for example, it is illegal to invoke
 815 * rcu_read_unlock_sched() from process context if the matching
 816 * rcu_read_lock_sched() was invoked from an NMI handler.
 817 */
 818static inline void rcu_read_lock_sched(void)
 819{
 820        preempt_disable();
 821        __acquire(RCU_SCHED);
 822        rcu_lock_acquire(&rcu_sched_lock_map);
 823        rcu_lockdep_assert(!rcu_is_cpu_idle(),
 824                           "rcu_read_lock_sched() used illegally while idle");
 825}
 826
 827/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
 828static inline notrace void rcu_read_lock_sched_notrace(void)
 829{
 830        preempt_disable_notrace();
 831        __acquire(RCU_SCHED);
 832}
 833
 834/*
 835 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
 836 *
 837 * See rcu_read_lock_sched for more information.
 838 */
 839static inline void rcu_read_unlock_sched(void)
 840{
 841        rcu_lockdep_assert(!rcu_is_cpu_idle(),
 842                           "rcu_read_unlock_sched() used illegally while idle");
 843        rcu_lock_release(&rcu_sched_lock_map);
 844        __release(RCU_SCHED);
 845        preempt_enable();
 846}
 847
 848/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
 849static inline notrace void rcu_read_unlock_sched_notrace(void)
 850{
 851        __release(RCU_SCHED);
 852        preempt_enable_notrace();
 853}
 854
 855/**
 856 * rcu_assign_pointer() - assign to RCU-protected pointer
 857 * @p: pointer to assign to
 858 * @v: value to assign (publish)
 859 *
 860 * Assigns the specified value to the specified RCU-protected
 861 * pointer, ensuring that any concurrent RCU readers will see
 862 * any prior initialization.
 863 *
 864 * Inserts memory barriers on architectures that require them
 865 * (which is most of them), and also prevents the compiler from
 866 * reordering the code that initializes the structure after the pointer
 867 * assignment.  More importantly, this call documents which pointers
 868 * will be dereferenced by RCU read-side code.
 869 *
 870 * In some special cases, you may use RCU_INIT_POINTER() instead
 871 * of rcu_assign_pointer().  RCU_INIT_POINTER() is a bit faster due
 872 * to the fact that it does not constrain either the CPU or the compiler.
 873 * That said, using RCU_INIT_POINTER() when you should have used
 874 * rcu_assign_pointer() is a very bad thing that results in
 875 * impossible-to-diagnose memory corruption.  So please be careful.
 876 * See the RCU_INIT_POINTER() comment header for details.
 877 */
 878#define rcu_assign_pointer(p, v) \
 879        __rcu_assign_pointer((p), (v), __rcu)
 880
 881/**
 882 * RCU_INIT_POINTER() - initialize an RCU protected pointer
 883 *
 884 * Initialize an RCU-protected pointer in special cases where readers
 885 * do not need ordering constraints on the CPU or the compiler.  These
 886 * special cases are:
 887 *
 888 * 1.   This use of RCU_INIT_POINTER() is NULLing out the pointer -or-
 889 * 2.   The caller has taken whatever steps are required to prevent
 890 *      RCU readers from concurrently accessing this pointer -or-
 891 * 3.   The referenced data structure has already been exposed to
 892 *      readers either at compile time or via rcu_assign_pointer() -and-
 893 *      a.      You have not made -any- reader-visible changes to
 894 *              this structure since then -or-
 895 *      b.      It is OK for readers accessing this structure from its
 896 *              new location to see the old state of the structure.  (For
 897 *              example, the changes were to statistical counters or to
 898 *              other state where exact synchronization is not required.)
 899 *
 900 * Failure to follow these rules governing use of RCU_INIT_POINTER() will
 901 * result in impossible-to-diagnose memory corruption.  As in the structures
 902 * will look OK in crash dumps, but any concurrent RCU readers might
 903 * see pre-initialized values of the referenced data structure.  So
 904 * please be very careful how you use RCU_INIT_POINTER()!!!
 905 *
 906 * If you are creating an RCU-protected linked structure that is accessed
 907 * by a single external-to-structure RCU-protected pointer, then you may
 908 * use RCU_INIT_POINTER() to initialize the internal RCU-protected
 909 * pointers, but you must use rcu_assign_pointer() to initialize the
 910 * external-to-structure pointer -after- you have completely initialized
 911 * the reader-accessible portions of the linked structure.
 912 */
 913#define RCU_INIT_POINTER(p, v) \
 914        do { \
 915                p = (typeof(*v) __force __rcu *)(v); \
 916        } while (0)
 917
 918/**
 919 * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
 920 *
 921 * GCC-style initialization for an RCU-protected pointer in a structure field.
 922 */
 923#define RCU_POINTER_INITIALIZER(p, v) \
 924                .p = (typeof(*v) __force __rcu *)(v)
 925
 926/*
 927 * Does the specified offset indicate that the corresponding rcu_head
 928 * structure can be handled by kfree_rcu()?
 929 */
 930#define __is_kfree_rcu_offset(offset) ((offset) < 4096)
 931
 932/*
 933 * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain.
 934 */
 935#define __kfree_rcu(head, offset) \
 936        do { \
 937                BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \
 938                kfree_call_rcu(head, (void (*)(struct rcu_head *))(unsigned long)(offset)); \
 939        } while (0)
 940
 941/**
 942 * kfree_rcu() - kfree an object after a grace period.
 943 * @ptr:        pointer to kfree
 944 * @rcu_head:   the name of the struct rcu_head within the type of @ptr.
 945 *
 946 * Many rcu callbacks functions just call kfree() on the base structure.
 947 * These functions are trivial, but their size adds up, and furthermore
 948 * when they are used in a kernel module, that module must invoke the
 949 * high-latency rcu_barrier() function at module-unload time.
 950 *
 951 * The kfree_rcu() function handles this issue.  Rather than encoding a
 952 * function address in the embedded rcu_head structure, kfree_rcu() instead
 953 * encodes the offset of the rcu_head structure within the base structure.
 954 * Because the functions are not allowed in the low-order 4096 bytes of
 955 * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
 956 * If the offset is larger than 4095 bytes, a compile-time error will
 957 * be generated in __kfree_rcu().  If this error is triggered, you can
 958 * either fall back to use of call_rcu() or rearrange the structure to
 959 * position the rcu_head structure into the first 4096 bytes.
 960 *
 961 * Note that the allowable offset might decrease in the future, for example,
 962 * to allow something like kmem_cache_free_rcu().
 963 *
 964 * The BUILD_BUG_ON check must not involve any function calls, hence the
 965 * checks are done in macros here.
 966 */
 967#define kfree_rcu(ptr, rcu_head)                                        \
 968        __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
 969
 970#endif /* __LINUX_RCUPDATE_H */
 971
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.