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 static inline int debug_lockdep_rcu_enabled(void)
 105 {
 106         return likely(rcu_scheduler_active && debug_locks);
 107 }
 108
 109 /**
 110  * rcu_read_lock_held - might we be in RCU read-side critical section?
 111  *
 112  * If CONFIG_PROVE_LOCKING is selected and enabled, returns nonzero iff in
 113  * an RCU read-side critical section.  In absence of CONFIG_PROVE_LOCKING,
 114  * this assumes we are in an RCU read-side critical section unless it can
 115  * prove otherwise.
 116  *
 117  * Check rcu_scheduler_active to prevent false positives during boot.
 118  */
 119 static inline int rcu_read_lock_held(void)
 120 {
 121         if (!debug_lockdep_rcu_enabled())
 122                 return 1;
 123         return lock_is_held(&rcu_lock_map);
 124 }
 125
 126 /*
 127  * rcu_read_lock_bh_held() is defined out of line to avoid #include-file
 128  * hell.
 129  */
 130 extern int rcu_read_lock_bh_held(void);
 131
 132 /**
 133  * rcu_read_lock_sched_held - might we be in RCU-sched read-side critical section?
 134  *
 135  * If CONFIG_PROVE_LOCKING is selected and enabled, returns nonzero iff in an
 136  * RCU-sched read-side critical section.  In absence of CONFIG_PROVE_LOCKING,
 137  * this assumes we are in an RCU-sched read-side critical section unless it
 138  * can prove otherwise.  Note that disabling of preemption (including
 139  * disabling irqs) counts as an RCU-sched read-side critical section.
 140  *
 141  * Check rcu_scheduler_active to prevent false positives during boot.
 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 /**
 197  * rcu_dereference_check - rcu_dereference with debug checking
 198  *
 199  * Do an rcu_dereference(), but check that the context is correct.
 200  * For example, rcu_dereference_check(gp, rcu_read_lock_held()) to
 201  * ensure that the rcu_dereference_check() executes within an RCU
 202  * read-side critical section.  It is also possible to check for
 203  * locks being held, for example, by using lockdep_is_held().
 204  */
 205 #define rcu_dereference_check(p, c) \
 206         ({ \
 207                 if (debug_lockdep_rcu_enabled() && !(c)) \
 208                         lockdep_rcu_dereference(__FILE__, __LINE__); \
 209                 rcu_dereference_raw(p); \
 210         })
 211
 212 #else /* #ifdef CONFIG_PROVE_RCU */
 213
 214 #define rcu_dereference_check(p, c)     rcu_dereference_raw(p)
 215
 216 #endif /* #else #ifdef CONFIG_PROVE_RCU */
 217
 218 /**
 219  * rcu_read_lock - mark the beginning of an RCU read-side critical section.
 220  *
 221  * When synchronize_rcu() is invoked on one CPU while other CPUs
 222  * are within RCU read-side critical sections, then the
 223  * synchronize_rcu() is guaranteed to block until after all the other
 224  * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
 225  * on one CPU while other CPUs are within RCU read-side critical
 226  * sections, invocation of the corresponding RCU callback is deferred
 227  * until after the all the other CPUs exit their critical sections.
 228  *
 229  * Note, however, that RCU callbacks are permitted to run concurrently
 230  * with RCU read-side critical sections.  One way that this can happen
 231  * is via the following sequence of events: (1) CPU 0 enters an RCU
 232  * read-side critical section, (2) CPU 1 invokes call_rcu() to register
 233  * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
 234  * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
 235  * callback is invoked.  This is legal, because the RCU read-side critical
 236  * section that was running concurrently with the call_rcu() (and which
 237  * therefore might be referencing something that the corresponding RCU
 238  * callback would free up) has completed before the corresponding
 239  * RCU callback is invoked.
 240  *
 241  * RCU read-side critical sections may be nested.  Any deferred actions
 242  * will be deferred until the outermost RCU read-side critical section
 243  * completes.
 244  *
 245  * It is illegal to block while in an RCU read-side critical section.
 246  */
 247 static inline void rcu_read_lock(void)
 248 {
 249         __rcu_read_lock();
 250         __acquire(RCU);
 251         rcu_read_acquire();
 252 }
 253
 254 /*
 255  * So where is rcu_write_lock()?  It does not exist, as there is no
 256  * way for writers to lock out RCU readers.  This is a feature, not
 257  * a bug -- this property is what provides RCU's performance benefits.
 258  * Of course, writers must coordinate with each other.  The normal
 259  * spinlock primitives work well for this, but any other technique may be
 260  * used as well.  RCU does not care how the writers keep out of each
 261  * others' way, as long as they do so.
 262  */
 263
 264 /**
 265  * rcu_read_unlock - marks the end of an RCU read-side critical section.
 266  *
 267  * See rcu_read_lock() for more information.
 268  */
 269 static inline void rcu_read_unlock(void)
 270 {
 271         rcu_read_release();
 272         __release(RCU);
 273         __rcu_read_unlock();
 274 }
 275
 276 /**
 277  * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
 278  *
 279  * This is equivalent of rcu_read_lock(), but to be used when updates
 280  * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
 281  * consider completion of a softirq handler to be a quiescent state,
 282  * a process in RCU read-side critical section must be protected by
 283  * disabling softirqs. Read-side critical sections in interrupt context
 284  * can use just rcu_read_lock().
 285  *
 286  */
 287 static inline void rcu_read_lock_bh(void)
 288 {
 289         __rcu_read_lock_bh();
 290         __acquire(RCU_BH);
 291         rcu_read_acquire_bh();
 292 }
 293
 294 /*
 295  * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
 296  *
 297  * See rcu_read_lock_bh() for more information.
 298  */
 299 static inline void rcu_read_unlock_bh(void)
 300 {
 301         rcu_read_release_bh();
 302         __release(RCU_BH);
 303         __rcu_read_unlock_bh();
 304 }
 305
 306 /**
 307  * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
 308  *
 309  * Should be used with either
 310  * - synchronize_sched()
 311  * or
 312  * - call_rcu_sched() and rcu_barrier_sched()
 313  * on the write-side to insure proper synchronization.
 314  */
 315 static inline void rcu_read_lock_sched(void)
 316 {
 317         preempt_disable();
 318         __acquire(RCU_SCHED);
 319         rcu_read_acquire_sched();
 320 }
 321
 322 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
 323 static inline notrace void rcu_read_lock_sched_notrace(void)
 324 {
 325         preempt_disable_notrace();
 326         __acquire(RCU_SCHED);
 327 }
 328
 329 /*
 330  * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
 331  *
 332  * See rcu_read_lock_sched for more information.
 333  */
 334 static inline void rcu_read_unlock_sched(void)
 335 {
 336         rcu_read_release_sched();
 337         __release(RCU_SCHED);
 338         preempt_enable();
 339 }
 340
 341 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
 342 static inline notrace void rcu_read_unlock_sched_notrace(void)
 343 {
 344         __release(RCU_SCHED);
 345         preempt_enable_notrace();
 346 }
 347
 348
 349 /**
 350  * rcu_dereference_raw - fetch an RCU-protected pointer
 351  *
 352  * The caller must be within some flavor of RCU read-side critical
 353  * section, or must be otherwise preventing the pointer from changing,
 354  * for example, by holding an appropriate lock.  This pointer may later
 355  * be safely dereferenced.  It is the caller's responsibility to have
 356  * done the right thing, as this primitive does no checking of any kind.
 357  *
 358  * Inserts memory barriers on architectures that require them
 359  * (currently only the Alpha), and, more importantly, documents
 360  * exactly which pointers are protected by RCU.
 361  */
 362 #define rcu_dereference_raw(p)  ({ \
 363                                 typeof(p) _________p1 = ACCESS_ONCE(p); \
 364                                 smp_read_barrier_depends(); \
 365                                 (_________p1); \
 366                                 })
 367
 368 /**
 369  * rcu_dereference - fetch an RCU-protected pointer, checking for RCU
 370  *
 371  * Makes rcu_dereference_check() do the dirty work.
 372  */
 373 #define rcu_dereference(p) \
 374         rcu_dereference_check(p, rcu_read_lock_held())
 375
 376 /**
 377  * rcu_dereference_bh - fetch an RCU-protected pointer, checking for RCU-bh
 378  *
 379  * Makes rcu_dereference_check() do the dirty work.
 380  */
 381 #define rcu_dereference_bh(p) \
 382                 rcu_dereference_check(p, rcu_read_lock_bh_held())
 383
 384 /**
 385  * rcu_dereference_sched - fetch RCU-protected pointer, checking for RCU-sched
 386  *
 387  * Makes rcu_dereference_check() do the dirty work.
 388  */
 389 #define rcu_dereference_sched(p) \
 390                 rcu_dereference_check(p, rcu_read_lock_sched_held())
 391
 392 /**
 393  * rcu_assign_pointer - assign (publicize) a pointer to a newly
 394  * initialized structure that will be dereferenced by RCU read-side
 395  * critical sections.  Returns the value assigned.
 396  *
 397  * Inserts memory barriers on architectures that require them
 398  * (pretty much all of them other than x86), and also prevents
 399  * the compiler from reordering the code that initializes the
 400  * structure after the pointer assignment.  More importantly, this
 401  * call documents which pointers will be dereferenced by RCU read-side
 402  * code.
 403  */
 404
 405 #define rcu_assign_pointer(p, v) \
 406         ({ \
 407                 if (!__builtin_constant_p(v) || \
 408                     ((v) != NULL)) \
 409                         smp_wmb(); \
 410                 (p) = (v); \
 411         })
 412
 413 /* Infrastructure to implement the synchronize_() primitives. */
 414
 415 struct rcu_synchronize {
 416         struct rcu_head head;
 417         struct completion completion;
 418 };
 419
 420 extern void wakeme_after_rcu(struct rcu_head  *head);
 421
 422 /**
 423  * call_rcu - Queue an RCU callback for invocation after a grace period.
 424  * @head: structure to be used for queueing the RCU updates.
 425  * @func: actual update function to be invoked after the grace period
 426  *
 427  * The update function will be invoked some time after a full grace
 428  * period elapses, in other words after all currently executing RCU
 429  * read-side critical sections have completed.  RCU read-side critical
 430  * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
 431  * and may be nested.
 432  */
 433 extern void call_rcu(struct rcu_head *head,
 434                               void (*func)(struct rcu_head *head));
 435
 436 /**
 437  * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
 438  * @head: structure to be used for queueing the RCU updates.
 439  * @func: actual update function to be invoked after the grace period
 440  *
 441  * The update function will be invoked some time after a full grace
 442  * period elapses, in other words after all currently executing RCU
 443  * read-side critical sections have completed. call_rcu_bh() assumes
 444  * that the read-side critical sections end on completion of a softirq
 445  * handler. This means that read-side critical sections in process
 446  * context must not be interrupted by softirqs. This interface is to be
 447  * used when most of the read-side critical sections are in softirq context.
 448  * RCU read-side critical sections are delimited by :
 449  *  - rcu_read_lock() and  rcu_read_unlock(), if in interrupt context.
 450  *  OR
 451  *  - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
 452  *  These may be nested.
 453  */
 454 extern void call_rcu_bh(struct rcu_head *head,
 455                         void (*func)(struct rcu_head *head));
 456
 457 #endif /* __LINUX_RCUPDATE_H */