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 /**
  45  * struct rcu_head - callback structure for use with RCU
  46  * @next: next update requests in a list
  47  * @func: actual update function to call after the grace period.
  48  */
  49 struct rcu_head {
  50         struct rcu_head *next;
  51         void (*func)(struct rcu_head *head);
  52 };
  53
  54 /* Exported common interfaces */
  55 extern void synchronize_rcu_bh(void);
  56 extern void synchronize_sched(void);
  57 extern void rcu_barrier(void);
  58 extern void rcu_barrier_bh(void);
  59 extern void rcu_barrier_sched(void);
  60 extern void synchronize_sched_expedited(void);
  61 extern int sched_expedited_torture_stats(char *page);
  62
  63 /* Internal to kernel */
  64 extern void rcu_init(void);
  65 extern int rcu_scheduler_active;
  66 extern void rcu_scheduler_starting(void);
  67
  68 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
  69 #include <linux/rcutree.h>
  70 #elif defined(CONFIG_TINY_RCU)
  71 #include <linux/rcutiny.h>
  72 #else
  73 #error "Unknown RCU implementation specified to kernel configuration"
  74 #endif
  75
  76 #define RCU_HEAD_INIT   { .next = NULL, .func = NULL }
  77 #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
  78 #define INIT_RCU_HEAD(ptr) do { \
  79        (ptr)->next = NULL; (ptr)->func = NULL; \
  80 } while (0)
  81
  82 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  83
  84 extern struct lockdep_map rcu_lock_map;
  85 # define rcu_read_acquire() \
  86                 lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
  87 # define rcu_read_release()     lock_release(&rcu_lock_map, 1, _THIS_IP_)
  88
  89 extern struct lockdep_map rcu_bh_lock_map;
  90 # define rcu_read_acquire_bh() \
  91                 lock_acquire(&rcu_bh_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
  92 # define rcu_read_release_bh()  lock_release(&rcu_bh_lock_map, 1, _THIS_IP_)
  93
  94 extern struct lockdep_map rcu_sched_lock_map;
  95 # define rcu_read_acquire_sched() \
  96                 lock_acquire(&rcu_sched_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
  97 # define rcu_read_release_sched() \
  98                 lock_release(&rcu_sched_lock_map, 1, _THIS_IP_)
  99
 100 /**
 101  * rcu_read_lock_held - might we be in RCU read-side critical section?
 102  *
 103  * If CONFIG_PROVE_LOCKING is selected and enabled, returns nonzero iff in
 104  * an RCU read-side critical section.  In absence of CONFIG_PROVE_LOCKING,
 105  * this assumes we are in an RCU read-side critical section unless it can
 106  * prove otherwise.
 107  */
 108 static inline int rcu_read_lock_held(void)
 109 {
 110         if (debug_locks)
 111                 return lock_is_held(&rcu_lock_map);
 112         return 1;
 113 }
 114
 115 /**
 116  * rcu_read_lock_bh_held - might we be in RCU-bh read-side critical section?
 117  *
 118  * If CONFIG_PROVE_LOCKING is selected and enabled, returns nonzero iff in
 119  * an RCU-bh read-side critical section.  In absence of CONFIG_PROVE_LOCKING,
 120  * this assumes we are in an RCU-bh read-side critical section unless it can
 121  * prove otherwise.
 122  */
 123 static inline int rcu_read_lock_bh_held(void)
 124 {
 125         if (debug_locks)
 126                 return lock_is_held(&rcu_bh_lock_map);
 127         return 1;
 128 }
 129
 130 /**
 131  * rcu_read_lock_sched_held - might we be in RCU-sched read-side critical section?
 132  *
 133  * If CONFIG_PROVE_LOCKING is selected and enabled, returns nonzero iff in an
 134  * RCU-sched read-side critical section.  In absence of CONFIG_PROVE_LOCKING,
 135  * this assumes we are in an RCU-sched read-side critical section unless it
 136  * can prove otherwise.  Note that disabling of preemption (including
 137  * disabling irqs) counts as an RCU-sched read-side critical section.
 138  */
 139 static inline int rcu_read_lock_sched_held(void)
 140 {
 141         int lockdep_opinion = 0;
 142
 143         if (debug_locks)
 144                 lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
 145         return lockdep_opinion || preempt_count() != 0 || !rcu_scheduler_active;
 146 }
 147
 148 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 149
 150 # define rcu_read_acquire()             do { } while (0)
 151 # define rcu_read_release()             do { } while (0)
 152 # define rcu_read_acquire_bh()          do { } while (0)
 153 # define rcu_read_release_bh()          do { } while (0)
 154 # define rcu_read_acquire_sched()       do { } while (0)
 155 # define rcu_read_release_sched()       do { } while (0)
 156
 157 static inline int rcu_read_lock_held(void)
 158 {
 159         return 1;
 160 }
 161
 162 static inline int rcu_read_lock_bh_held(void)
 163 {
 164         return 1;
 165 }
 166
 167 static inline int rcu_read_lock_sched_held(void)
 168 {
 169         return preempt_count() != 0 || !rcu_scheduler_active;
 170 }
 171
 172 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 173
 174 #ifdef CONFIG_PROVE_RCU
 175
 176 /**
 177  * rcu_dereference_check - rcu_dereference with debug checking
 178  *
 179  * Do an rcu_dereference(), but check that the context is correct.
 180  * For example, rcu_dereference_check(gp, rcu_read_lock_held()) to
 181  * ensure that the rcu_dereference_check() executes within an RCU
 182  * read-side critical section.  It is also possible to check for
 183  * locks being held, for example, by using lockdep_is_held().
 184  */
 185 #define rcu_dereference_check(p, c) \
 186         ({ \
 187                 if (debug_locks && !(c)) \
 188                         lockdep_rcu_dereference(__FILE__, __LINE__); \
 189                 rcu_dereference_raw(p); \
 190         })
 191
 192 #else /* #ifdef CONFIG_PROVE_RCU */
 193
 194 #define rcu_dereference_check(p, c)     rcu_dereference_raw(p)
 195
 196 #endif /* #else #ifdef CONFIG_PROVE_RCU */
 197
 198 /**
 199  * rcu_read_lock - mark the beginning of an RCU read-side critical section.
 200  *
 201  * When synchronize_rcu() is invoked on one CPU while other CPUs
 202  * are within RCU read-side critical sections, then the
 203  * synchronize_rcu() is guaranteed to block until after all the other
 204  * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
 205  * on one CPU while other CPUs are within RCU read-side critical
 206  * sections, invocation of the corresponding RCU callback is deferred
 207  * until after the all the other CPUs exit their critical sections.
 208  *
 209  * Note, however, that RCU callbacks are permitted to run concurrently
 210  * with RCU read-side critical sections.  One way that this can happen
 211  * is via the following sequence of events: (1) CPU 0 enters an RCU
 212  * read-side critical section, (2) CPU 1 invokes call_rcu() to register
 213  * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
 214  * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
 215  * callback is invoked.  This is legal, because the RCU read-side critical
 216  * section that was running concurrently with the call_rcu() (and which
 217  * therefore might be referencing something that the corresponding RCU
 218  * callback would free up) has completed before the corresponding
 219  * RCU callback is invoked.
 220  *
 221  * RCU read-side critical sections may be nested.  Any deferred actions
 222  * will be deferred until the outermost RCU read-side critical section
 223  * completes.
 224  *
 225  * It is illegal to block while in an RCU read-side critical section.
 226  */
 227 static inline void rcu_read_lock(void)
 228 {
 229         __rcu_read_lock();
 230         __acquire(RCU);
 231         rcu_read_acquire();
 232 }
 233
 234 /*
 235  * So where is rcu_write_lock()?  It does not exist, as there is no
 236  * way for writers to lock out RCU readers.  This is a feature, not
 237  * a bug -- this property is what provides RCU's performance benefits.
 238  * Of course, writers must coordinate with each other.  The normal
 239  * spinlock primitives work well for this, but any other technique may be
 240  * used as well.  RCU does not care how the writers keep out of each
 241  * others' way, as long as they do so.
 242  */
 243
 244 /**
 245  * rcu_read_unlock - marks the end of an RCU read-side critical section.
 246  *
 247  * See rcu_read_lock() for more information.
 248  */
 249 static inline void rcu_read_unlock(void)
 250 {
 251         rcu_read_release();
 252         __release(RCU);
 253         __rcu_read_unlock();
 254 }
 255
 256 /**
 257  * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
 258  *
 259  * This is equivalent of rcu_read_lock(), but to be used when updates
 260  * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
 261  * consider completion of a softirq handler to be a quiescent state,
 262  * a process in RCU read-side critical section must be protected by
 263  * disabling softirqs. Read-side critical sections in interrupt context
 264  * can use just rcu_read_lock().
 265  *
 266  */
 267 static inline void rcu_read_lock_bh(void)
 268 {
 269         __rcu_read_lock_bh();
 270         __acquire(RCU_BH);
 271         rcu_read_acquire_bh();
 272 }
 273
 274 /*
 275  * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
 276  *
 277  * See rcu_read_lock_bh() for more information.
 278  */
 279 static inline void rcu_read_unlock_bh(void)
 280 {
 281         rcu_read_release_bh();
 282         __release(RCU_BH);
 283         __rcu_read_unlock_bh();
 284 }
 285
 286 /**
 287  * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
 288  *
 289  * Should be used with either
 290  * - synchronize_sched()
 291  * or
 292  * - call_rcu_sched() and rcu_barrier_sched()
 293  * on the write-side to insure proper synchronization.
 294  */
 295 static inline void rcu_read_lock_sched(void)
 296 {
 297         preempt_disable();
 298         __acquire(RCU_SCHED);
 299         rcu_read_acquire_sched();
 300 }
 301
 302 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
 303 static inline notrace void rcu_read_lock_sched_notrace(void)
 304 {
 305         preempt_disable_notrace();
 306         __acquire(RCU_SCHED);
 307 }
 308
 309 /*
 310  * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
 311  *
 312  * See rcu_read_lock_sched for more information.
 313  */
 314 static inline void rcu_read_unlock_sched(void)
 315 {
 316         rcu_read_release_sched();
 317         __release(RCU_SCHED);
 318         preempt_enable();
 319 }
 320
 321 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
 322 static inline notrace void rcu_read_unlock_sched_notrace(void)
 323 {
 324         __release(RCU_SCHED);
 325         preempt_enable_notrace();
 326 }
 327
 328
 329 /**
 330  * rcu_dereference_raw - fetch an RCU-protected pointer
 331  *
 332  * The caller must be within some flavor of RCU read-side critical
 333  * section, or must be otherwise preventing the pointer from changing,
 334  * for example, by holding an appropriate lock.  This pointer may later
 335  * be safely dereferenced.  It is the caller's responsibility to have
 336  * done the right thing, as this primitive does no checking of any kind.
 337  *
 338  * Inserts memory barriers on architectures that require them
 339  * (currently only the Alpha), and, more importantly, documents
 340  * exactly which pointers are protected by RCU.
 341  */
 342 #define rcu_dereference_raw(p)  ({ \
 343                                 typeof(p) _________p1 = ACCESS_ONCE(p); \
 344                                 smp_read_barrier_depends(); \
 345                                 (_________p1); \
 346                                 })
 347
 348 /**
 349  * rcu_dereference - fetch an RCU-protected pointer, checking for RCU
 350  *
 351  * Makes rcu_dereference_check() do the dirty work.
 352  */
 353 #define rcu_dereference(p) \
 354         rcu_dereference_check(p, rcu_read_lock_held())
 355
 356 /**
 357  * rcu_dereference_bh - fetch an RCU-protected pointer, checking for RCU-bh
 358  *
 359  * Makes rcu_dereference_check() do the dirty work.
 360  */
 361 #define rcu_dereference_bh(p) \
 362                 rcu_dereference_check(p, rcu_read_lock_bh_held())
 363
 364 /**
 365  * rcu_dereference_sched - fetch RCU-protected pointer, checking for RCU-sched
 366  *
 367  * Makes rcu_dereference_check() do the dirty work.
 368  */
 369 #define rcu_dereference_sched(p) \
 370                 rcu_dereference_check(p, rcu_read_lock_sched_held())
 371
 372 /**
 373  * rcu_assign_pointer - assign (publicize) a pointer to a newly
 374  * initialized structure that will be dereferenced by RCU read-side
 375  * critical sections.  Returns the value assigned.
 376  *
 377  * Inserts memory barriers on architectures that require them
 378  * (pretty much all of them other than x86), and also prevents
 379  * the compiler from reordering the code that initializes the
 380  * structure after the pointer assignment.  More importantly, this
 381  * call documents which pointers will be dereferenced by RCU read-side
 382  * code.
 383  */
 384
 385 #define rcu_assign_pointer(p, v) \
 386         ({ \
 387                 if (!__builtin_constant_p(v) || \
 388                     ((v) != NULL)) \
 389                         smp_wmb(); \
 390                 (p) = (v); \
 391         })
 392
 393 /* Infrastructure to implement the synchronize_() primitives. */
 394
 395 struct rcu_synchronize {
 396         struct rcu_head head;
 397         struct completion completion;
 398 };
 399
 400 extern void wakeme_after_rcu(struct rcu_head  *head);
 401
 402 /**
 403  * call_rcu - Queue an RCU callback for invocation after a grace period.
 404  * @head: structure to be used for queueing the RCU updates.
 405  * @func: actual update function to be invoked after the grace period
 406  *
 407  * The update function will be invoked some time after a full grace
 408  * period elapses, in other words after all currently executing RCU
 409  * read-side critical sections have completed.  RCU read-side critical
 410  * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
 411  * and may be nested.
 412  */
 413 extern void call_rcu(struct rcu_head *head,
 414                               void (*func)(struct rcu_head *head));
 415
 416 /**
 417  * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
 418  * @head: structure to be used for queueing the RCU updates.
 419  * @func: actual update function to be invoked after the grace period
 420  *
 421  * The update function will be invoked some time after a full grace
 422  * period elapses, in other words after all currently executing RCU
 423  * read-side critical sections have completed. call_rcu_bh() assumes
 424  * that the read-side critical sections end on completion of a softirq
 425  * handler. This means that read-side critical sections in process
 426  * context must not be interrupted by softirqs. This interface is to be
 427  * used when most of the read-side critical sections are in softirq context.
 428  * RCU read-side critical sections are delimited by :
 429  *  - rcu_read_lock() and  rcu_read_unlock(), if in interrupt context.
 430  *  OR
 431  *  - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
 432  *  These may be nested.
 433  */
 434 extern void call_rcu_bh(struct rcu_head *head,
 435                         void (*func)(struct rcu_head *head));
 436
 437 #endif /* __LINUX_RCUPDATE_H */