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 /**
 105  * rcu_read_lock_held - might we be in RCU read-side critical section?
 106  *
 107  * If CONFIG_PROVE_LOCKING is selected and enabled, returns nonzero iff in
 108  * an RCU read-side critical section.  In absence of CONFIG_PROVE_LOCKING,
 109  * this assumes we are in an RCU read-side critical section unless it can
 110  * prove otherwise.
 111  */
 112 static inline int rcu_read_lock_held(void)
 113 {
 114         if (debug_locks)
 115                 return lock_is_held(&rcu_lock_map);
 116         return 1;
 117 }
 118
 119 /**
 120  * rcu_read_lock_bh_held - might we be in RCU-bh read-side critical section?
 121  *
 122  * If CONFIG_PROVE_LOCKING is selected and enabled, returns nonzero iff in
 123  * an RCU-bh read-side critical section.  In absence of CONFIG_PROVE_LOCKING,
 124  * this assumes we are in an RCU-bh read-side critical section unless it can
 125  * prove otherwise.
 126  */
 127 static inline int rcu_read_lock_bh_held(void)
 128 {
 129         if (debug_locks)
 130                 return lock_is_held(&rcu_bh_lock_map);
 131         return 1;
 132 }
 133
 134 /**
 135  * rcu_read_lock_sched_held - might we be in RCU-sched read-side critical section?
 136  *
 137  * If CONFIG_PROVE_LOCKING is selected and enabled, returns nonzero iff in an
 138  * RCU-sched read-side critical section.  In absence of CONFIG_PROVE_LOCKING,
 139  * this assumes we are in an RCU-sched read-side critical section unless it
 140  * can prove otherwise.  Note that disabling of preemption (including
 141  * disabling irqs) counts as an RCU-sched read-side critical section.
 142  */
 143 static inline int rcu_read_lock_sched_held(void)
 144 {
 145         int lockdep_opinion = 0;
 146
 147         if (debug_locks)
 148                 lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
 149         return lockdep_opinion || preempt_count() != 0 || !rcu_scheduler_active;
 150 }
 151
 152 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 153
 154 # define rcu_read_acquire()             do { } while (0)
 155 # define rcu_read_release()             do { } while (0)
 156 # define rcu_read_acquire_bh()          do { } while (0)
 157 # define rcu_read_release_bh()          do { } while (0)
 158 # define rcu_read_acquire_sched()       do { } while (0)
 159 # define rcu_read_release_sched()       do { } while (0)
 160
 161 static inline int rcu_read_lock_held(void)
 162 {
 163         return 1;
 164 }
 165
 166 static inline int rcu_read_lock_bh_held(void)
 167 {
 168         return 1;
 169 }
 170
 171 static inline int rcu_read_lock_sched_held(void)
 172 {
 173         return preempt_count() != 0 || !rcu_scheduler_active;
 174 }
 175
 176 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 177
 178 #ifdef CONFIG_PROVE_RCU
 179
 180 /**
 181  * rcu_dereference_check - rcu_dereference with debug checking
 182  *
 183  * Do an rcu_dereference(), but check that the context is correct.
 184  * For example, rcu_dereference_check(gp, rcu_read_lock_held()) to
 185  * ensure that the rcu_dereference_check() executes within an RCU
 186  * read-side critical section.  It is also possible to check for
 187  * locks being held, for example, by using lockdep_is_held().
 188  */
 189 #define rcu_dereference_check(p, c) \
 190         ({ \
 191                 if (debug_locks && !(c)) \
 192                         lockdep_rcu_dereference(__FILE__, __LINE__); \
 193                 rcu_dereference_raw(p); \
 194         })
 195
 196 #else /* #ifdef CONFIG_PROVE_RCU */
 197
 198 #define rcu_dereference_check(p, c)     rcu_dereference_raw(p)
 199
 200 #endif /* #else #ifdef CONFIG_PROVE_RCU */
 201
 202 /**
 203  * rcu_read_lock - mark the beginning of an RCU read-side critical section.
 204  *
 205  * When synchronize_rcu() is invoked on one CPU while other CPUs
 206  * are within RCU read-side critical sections, then the
 207  * synchronize_rcu() is guaranteed to block until after all the other
 208  * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
 209  * on one CPU while other CPUs are within RCU read-side critical
 210  * sections, invocation of the corresponding RCU callback is deferred
 211  * until after the all the other CPUs exit their critical sections.
 212  *
 213  * Note, however, that RCU callbacks are permitted to run concurrently
 214  * with RCU read-side critical sections.  One way that this can happen
 215  * is via the following sequence of events: (1) CPU 0 enters an RCU
 216  * read-side critical section, (2) CPU 1 invokes call_rcu() to register
 217  * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
 218  * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
 219  * callback is invoked.  This is legal, because the RCU read-side critical
 220  * section that was running concurrently with the call_rcu() (and which
 221  * therefore might be referencing something that the corresponding RCU
 222  * callback would free up) has completed before the corresponding
 223  * RCU callback is invoked.
 224  *
 225  * RCU read-side critical sections may be nested.  Any deferred actions
 226  * will be deferred until the outermost RCU read-side critical section
 227  * completes.
 228  *
 229  * It is illegal to block while in an RCU read-side critical section.
 230  */
 231 static inline void rcu_read_lock(void)
 232 {
 233         __rcu_read_lock();
 234         __acquire(RCU);
 235         rcu_read_acquire();
 236 }
 237
 238 /*
 239  * So where is rcu_write_lock()?  It does not exist, as there is no
 240  * way for writers to lock out RCU readers.  This is a feature, not
 241  * a bug -- this property is what provides RCU's performance benefits.
 242  * Of course, writers must coordinate with each other.  The normal
 243  * spinlock primitives work well for this, but any other technique may be
 244  * used as well.  RCU does not care how the writers keep out of each
 245  * others' way, as long as they do so.
 246  */
 247
 248 /**
 249  * rcu_read_unlock - marks the end of an RCU read-side critical section.
 250  *
 251  * See rcu_read_lock() for more information.
 252  */
 253 static inline void rcu_read_unlock(void)
 254 {
 255         rcu_read_release();
 256         __release(RCU);
 257         __rcu_read_unlock();
 258 }
 259
 260 /**
 261  * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
 262  *
 263  * This is equivalent of rcu_read_lock(), but to be used when updates
 264  * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
 265  * consider completion of a softirq handler to be a quiescent state,
 266  * a process in RCU read-side critical section must be protected by
 267  * disabling softirqs. Read-side critical sections in interrupt context
 268  * can use just rcu_read_lock().
 269  *
 270  */
 271 static inline void rcu_read_lock_bh(void)
 272 {
 273         __rcu_read_lock_bh();
 274         __acquire(RCU_BH);
 275         rcu_read_acquire_bh();
 276 }
 277
 278 /*
 279  * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
 280  *
 281  * See rcu_read_lock_bh() for more information.
 282  */
 283 static inline void rcu_read_unlock_bh(void)
 284 {
 285         rcu_read_release_bh();
 286         __release(RCU_BH);
 287         __rcu_read_unlock_bh();
 288 }
 289
 290 /**
 291  * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
 292  *
 293  * Should be used with either
 294  * - synchronize_sched()
 295  * or
 296  * - call_rcu_sched() and rcu_barrier_sched()
 297  * on the write-side to insure proper synchronization.
 298  */
 299 static inline void rcu_read_lock_sched(void)
 300 {
 301         preempt_disable();
 302         __acquire(RCU_SCHED);
 303         rcu_read_acquire_sched();
 304 }
 305
 306 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
 307 static inline notrace void rcu_read_lock_sched_notrace(void)
 308 {
 309         preempt_disable_notrace();
 310         __acquire(RCU_SCHED);
 311 }
 312
 313 /*
 314  * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
 315  *
 316  * See rcu_read_lock_sched for more information.
 317  */
 318 static inline void rcu_read_unlock_sched(void)
 319 {
 320         rcu_read_release_sched();
 321         __release(RCU_SCHED);
 322         preempt_enable();
 323 }
 324
 325 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
 326 static inline notrace void rcu_read_unlock_sched_notrace(void)
 327 {
 328         __release(RCU_SCHED);
 329         preempt_enable_notrace();
 330 }
 331
 332
 333 /**
 334  * rcu_dereference_raw - fetch an RCU-protected pointer
 335  *
 336  * The caller must be within some flavor of RCU read-side critical
 337  * section, or must be otherwise preventing the pointer from changing,
 338  * for example, by holding an appropriate lock.  This pointer may later
 339  * be safely dereferenced.  It is the caller's responsibility to have
 340  * done the right thing, as this primitive does no checking of any kind.
 341  *
 342  * Inserts memory barriers on architectures that require them
 343  * (currently only the Alpha), and, more importantly, documents
 344  * exactly which pointers are protected by RCU.
 345  */
 346 #define rcu_dereference_raw(p)  ({ \
 347                                 typeof(p) _________p1 = ACCESS_ONCE(p); \
 348                                 smp_read_barrier_depends(); \
 349                                 (_________p1); \
 350                                 })
 351
 352 /**
 353  * rcu_dereference - fetch an RCU-protected pointer, checking for RCU
 354  *
 355  * Makes rcu_dereference_check() do the dirty work.
 356  */
 357 #define rcu_dereference(p) \
 358         rcu_dereference_check(p, rcu_read_lock_held())
 359
 360 /**
 361  * rcu_dereference_bh - fetch an RCU-protected pointer, checking for RCU-bh
 362  *
 363  * Makes rcu_dereference_check() do the dirty work.
 364  */
 365 #define rcu_dereference_bh(p) \
 366                 rcu_dereference_check(p, rcu_read_lock_bh_held())
 367
 368 /**
 369  * rcu_dereference_sched - fetch RCU-protected pointer, checking for RCU-sched
 370  *
 371  * Makes rcu_dereference_check() do the dirty work.
 372  */
 373 #define rcu_dereference_sched(p) \
 374                 rcu_dereference_check(p, rcu_read_lock_sched_held())
 375
 376 /**
 377  * rcu_assign_pointer - assign (publicize) a pointer to a newly
 378  * initialized structure that will be dereferenced by RCU read-side
 379  * critical sections.  Returns the value assigned.
 380  *
 381  * Inserts memory barriers on architectures that require them
 382  * (pretty much all of them other than x86), and also prevents
 383  * the compiler from reordering the code that initializes the
 384  * structure after the pointer assignment.  More importantly, this
 385  * call documents which pointers will be dereferenced by RCU read-side
 386  * code.
 387  */
 388
 389 #define rcu_assign_pointer(p, v) \
 390         ({ \
 391                 if (!__builtin_constant_p(v) || \
 392                     ((v) != NULL)) \
 393                         smp_wmb(); \
 394                 (p) = (v); \
 395         })
 396
 397 /* Infrastructure to implement the synchronize_() primitives. */
 398
 399 struct rcu_synchronize {
 400         struct rcu_head head;
 401         struct completion completion;
 402 };
 403
 404 extern void wakeme_after_rcu(struct rcu_head  *head);
 405
 406 /**
 407  * call_rcu - Queue an RCU callback for invocation after a grace period.
 408  * @head: structure to be used for queueing the RCU updates.
 409  * @func: actual update function to be invoked after the grace period
 410  *
 411  * The update function will be invoked some time after a full grace
 412  * period elapses, in other words after all currently executing RCU
 413  * read-side critical sections have completed.  RCU read-side critical
 414  * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
 415  * and may be nested.
 416  */
 417 extern void call_rcu(struct rcu_head *head,
 418                               void (*func)(struct rcu_head *head));
 419
 420 /**
 421  * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
 422  * @head: structure to be used for queueing the RCU updates.
 423  * @func: actual update function to be invoked after the grace period
 424  *
 425  * The update function will be invoked some time after a full grace
 426  * period elapses, in other words after all currently executing RCU
 427  * read-side critical sections have completed. call_rcu_bh() assumes
 428  * that the read-side critical sections end on completion of a softirq
 429  * handler. This means that read-side critical sections in process
 430  * context must not be interrupted by softirqs. This interface is to be
 431  * used when most of the read-side critical sections are in softirq context.
 432  * RCU read-side critical sections are delimited by :
 433  *  - rcu_read_lock() and  rcu_read_unlock(), if in interrupt context.
 434  *  OR
 435  *  - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
 436  *  These may be nested.
 437  */
 438 extern void call_rcu_bh(struct rcu_head *head,
 439                         void (*func)(struct rcu_head *head));
 440
 441 #endif /* __LINUX_RCUPDATE_H */