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 extern struct lockdep_map rcu_lock_map;
  82 # define rcu_read_acquire()     \
  83                         lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
  84 # define rcu_read_release()     lock_release(&rcu_lock_map, 1, _THIS_IP_)
  85 #else
  86 # define rcu_read_acquire()     do { } while (0)
  87 # define rcu_read_release()     do { } while (0)
  88 #endif
  89
  90 /**
  91  * rcu_read_lock - mark the beginning of an RCU read-side critical section.
  92  *
  93  * When synchronize_rcu() is invoked on one CPU while other CPUs
  94  * are within RCU read-side critical sections, then the
  95  * synchronize_rcu() is guaranteed to block until after all the other
  96  * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
  97  * on one CPU while other CPUs are within RCU read-side critical
  98  * sections, invocation of the corresponding RCU callback is deferred
  99  * until after the all the other CPUs exit their critical sections.
 100  *
 101  * Note, however, that RCU callbacks are permitted to run concurrently
 102  * with RCU read-side critical sections.  One way that this can happen
 103  * is via the following sequence of events: (1) CPU 0 enters an RCU
 104  * read-side critical section, (2) CPU 1 invokes call_rcu() to register
 105  * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
 106  * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
 107  * callback is invoked.  This is legal, because the RCU read-side critical
 108  * section that was running concurrently with the call_rcu() (and which
 109  * therefore might be referencing something that the corresponding RCU
 110  * callback would free up) has completed before the corresponding
 111  * RCU callback is invoked.
 112  *
 113  * RCU read-side critical sections may be nested.  Any deferred actions
 114  * will be deferred until the outermost RCU read-side critical section
 115  * completes.
 116  *
 117  * It is illegal to block while in an RCU read-side critical section.
 118  */
 119 static inline void rcu_read_lock(void)
 120 {
 121         __rcu_read_lock();
 122         __acquire(RCU);
 123         rcu_read_acquire();
 124 }
 125
 126 /*
 127  * So where is rcu_write_lock()?  It does not exist, as there is no
 128  * way for writers to lock out RCU readers.  This is a feature, not
 129  * a bug -- this property is what provides RCU's performance benefits.
 130  * Of course, writers must coordinate with each other.  The normal
 131  * spinlock primitives work well for this, but any other technique may be
 132  * used as well.  RCU does not care how the writers keep out of each
 133  * others' way, as long as they do so.
 134  */
 135
 136 /**
 137  * rcu_read_unlock - marks the end of an RCU read-side critical section.
 138  *
 139  * See rcu_read_lock() for more information.
 140  */
 141 static inline void rcu_read_unlock(void)
 142 {
 143         rcu_read_release();
 144         __release(RCU);
 145         __rcu_read_unlock();
 146 }
 147
 148 /**
 149  * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
 150  *
 151  * This is equivalent of rcu_read_lock(), but to be used when updates
 152  * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
 153  * consider completion of a softirq handler to be a quiescent state,
 154  * a process in RCU read-side critical section must be protected by
 155  * disabling softirqs. Read-side critical sections in interrupt context
 156  * can use just rcu_read_lock().
 157  *
 158  */
 159 static inline void rcu_read_lock_bh(void)
 160 {
 161         __rcu_read_lock_bh();
 162         __acquire(RCU_BH);
 163         rcu_read_acquire();
 164 }
 165
 166 /*
 167  * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
 168  *
 169  * See rcu_read_lock_bh() for more information.
 170  */
 171 static inline void rcu_read_unlock_bh(void)
 172 {
 173         rcu_read_release();
 174         __release(RCU_BH);
 175         __rcu_read_unlock_bh();
 176 }
 177
 178 /**
 179  * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
 180  *
 181  * Should be used with either
 182  * - synchronize_sched()
 183  * or
 184  * - call_rcu_sched() and rcu_barrier_sched()
 185  * on the write-side to insure proper synchronization.
 186  */
 187 static inline void rcu_read_lock_sched(void)
 188 {
 189         preempt_disable();
 190         __acquire(RCU_SCHED);
 191         rcu_read_acquire();
 192 }
 193
 194 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
 195 static inline notrace void rcu_read_lock_sched_notrace(void)
 196 {
 197         preempt_disable_notrace();
 198         __acquire(RCU_SCHED);
 199 }
 200
 201 /*
 202  * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
 203  *
 204  * See rcu_read_lock_sched for more information.
 205  */
 206 static inline void rcu_read_unlock_sched(void)
 207 {
 208         rcu_read_release();
 209         __release(RCU_SCHED);
 210         preempt_enable();
 211 }
 212
 213 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
 214 static inline notrace void rcu_read_unlock_sched_notrace(void)
 215 {
 216         __release(RCU_SCHED);
 217         preempt_enable_notrace();
 218 }
 219
 220
 221 /**
 222  * rcu_dereference - fetch an RCU-protected pointer in an
 223  * RCU read-side critical section.  This pointer may later
 224  * be safely dereferenced.
 225  *
 226  * Inserts memory barriers on architectures that require them
 227  * (currently only the Alpha), and, more importantly, documents
 228  * exactly which pointers are protected by RCU.
 229  */
 230
 231 #define rcu_dereference(p)     ({ \
 232                                 typeof(p) _________p1 = ACCESS_ONCE(p); \
 233                                 smp_read_barrier_depends(); \
 234                                 (_________p1); \
 235                                 })
 236
 237 /**
 238  * rcu_assign_pointer - assign (publicize) a pointer to a newly
 239  * initialized structure that will be dereferenced by RCU read-side
 240  * critical sections.  Returns the value assigned.
 241  *
 242  * Inserts memory barriers on architectures that require them
 243  * (pretty much all of them other than x86), and also prevents
 244  * the compiler from reordering the code that initializes the
 245  * structure after the pointer assignment.  More importantly, this
 246  * call documents which pointers will be dereferenced by RCU read-side
 247  * code.
 248  */
 249
 250 #define rcu_assign_pointer(p, v) \
 251         ({ \
 252                 if (!__builtin_constant_p(v) || \
 253                     ((v) != NULL)) \
 254                         smp_wmb(); \
 255                 (p) = (v); \
 256         })
 257
 258 /* Infrastructure to implement the synchronize_() primitives. */
 259
 260 struct rcu_synchronize {
 261         struct rcu_head head;
 262         struct completion completion;
 263 };
 264
 265 extern void wakeme_after_rcu(struct rcu_head  *head);
 266
 267 /**
 268  * call_rcu - Queue an RCU callback for invocation after a grace period.
 269  * @head: structure to be used for queueing the RCU updates.
 270  * @func: actual update function to be invoked after the grace period
 271  *
 272  * The update function will be invoked some time after a full grace
 273  * period elapses, in other words after all currently executing RCU
 274  * read-side critical sections have completed.  RCU read-side critical
 275  * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
 276  * and may be nested.
 277  */
 278 extern void call_rcu(struct rcu_head *head,
 279                               void (*func)(struct rcu_head *head));
 280
 281 /**
 282  * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
 283  * @head: structure to be used for queueing the RCU updates.
 284  * @func: actual update function to be invoked after the grace period
 285  *
 286  * The update function will be invoked some time after a full grace
 287  * period elapses, in other words after all currently executing RCU
 288  * read-side critical sections have completed. call_rcu_bh() assumes
 289  * that the read-side critical sections end on completion of a softirq
 290  * handler. This means that read-side critical sections in process
 291  * context must not be interrupted by softirqs. This interface is to be
 292  * used when most of the read-side critical sections are in softirq context.
 293  * RCU read-side critical sections are delimited by :
 294  *  - rcu_read_lock() and  rcu_read_unlock(), if in interrupt context.
 295  *  OR
 296  *  - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
 297  *  These may be nested.
 298  */
 299 extern void call_rcu_bh(struct rcu_head *head,
 300                         void (*func)(struct rcu_head *head));
 301
 302 #endif /* __LINUX_RCUPDATE_H */