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