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 #ifdef CONFIG_TREE_PREEMPT_RCU
  56 extern void synchronize_rcu(void);
  57 #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
  58 #define synchronize_rcu synchronize_sched
  59 #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
  60 extern void synchronize_rcu_bh(void);
  61 extern void synchronize_sched(void);
  62 extern void rcu_barrier(void);
  63 extern void rcu_barrier_bh(void);
  64 extern void rcu_barrier_sched(void);
  65 extern void synchronize_sched_expedited(void);
  66 extern int sched_expedited_torture_stats(char *page);
  67
  68 /* Internal to kernel */
  69 extern void rcu_init(void);
  70 extern void rcu_scheduler_starting(void);
  71 extern int rcu_needs_cpu(int cpu);
  72 extern int rcu_scheduler_active;
  73
  74 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
  75 #include <linux/rcutree.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 extern struct lockdep_map rcu_lock_map;
  88 # define rcu_read_acquire()     \
  89                         lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
  90 # define rcu_read_release()     lock_release(&rcu_lock_map, 1, _THIS_IP_)
  91 #else
  92 # define rcu_read_acquire()     do { } while (0)
  93 # define rcu_read_release()     do { } while (0)
  94 #endif
  95
  96 /**
  97  * rcu_read_lock - mark the beginning of an RCU read-side critical section.
  98  *
  99  * When synchronize_rcu() is invoked on one CPU while other CPUs
 100  * are within RCU read-side critical sections, then the
 101  * synchronize_rcu() is guaranteed to block until after all the other
 102  * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
 103  * on one CPU while other CPUs are within RCU read-side critical
 104  * sections, invocation of the corresponding RCU callback is deferred
 105  * until after the all the other CPUs exit their critical sections.
 106  *
 107  * Note, however, that RCU callbacks are permitted to run concurrently
 108  * with RCU read-side critical sections.  One way that this can happen
 109  * is via the following sequence of events: (1) CPU 0 enters an RCU
 110  * read-side critical section, (2) CPU 1 invokes call_rcu() to register
 111  * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
 112  * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
 113  * callback is invoked.  This is legal, because the RCU read-side critical
 114  * section that was running concurrently with the call_rcu() (and which
 115  * therefore might be referencing something that the corresponding RCU
 116  * callback would free up) has completed before the corresponding
 117  * RCU callback is invoked.
 118  *
 119  * RCU read-side critical sections may be nested.  Any deferred actions
 120  * will be deferred until the outermost RCU read-side critical section
 121  * completes.
 122  *
 123  * It is illegal to block while in an RCU read-side critical section.
 124  */
 125 static inline void rcu_read_lock(void)
 126 {
 127         __rcu_read_lock();
 128         __acquire(RCU);
 129         rcu_read_acquire();
 130 }
 131
 132 /*
 133  * So where is rcu_write_lock()?  It does not exist, as there is no
 134  * way for writers to lock out RCU readers.  This is a feature, not
 135  * a bug -- this property is what provides RCU's performance benefits.
 136  * Of course, writers must coordinate with each other.  The normal
 137  * spinlock primitives work well for this, but any other technique may be
 138  * used as well.  RCU does not care how the writers keep out of each
 139  * others' way, as long as they do so.
 140  */
 141
 142 /**
 143  * rcu_read_unlock - marks the end of an RCU read-side critical section.
 144  *
 145  * See rcu_read_lock() for more information.
 146  */
 147 static inline void rcu_read_unlock(void)
 148 {
 149         rcu_read_release();
 150         __release(RCU);
 151         __rcu_read_unlock();
 152 }
 153
 154 /**
 155  * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
 156  *
 157  * This is equivalent of rcu_read_lock(), but to be used when updates
 158  * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
 159  * consider completion of a softirq handler to be a quiescent state,
 160  * a process in RCU read-side critical section must be protected by
 161  * disabling softirqs. Read-side critical sections in interrupt context
 162  * can use just rcu_read_lock().
 163  *
 164  */
 165 static inline void rcu_read_lock_bh(void)
 166 {
 167         __rcu_read_lock_bh();
 168         __acquire(RCU_BH);
 169         rcu_read_acquire();
 170 }
 171
 172 /*
 173  * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
 174  *
 175  * See rcu_read_lock_bh() for more information.
 176  */
 177 static inline void rcu_read_unlock_bh(void)
 178 {
 179         rcu_read_release();
 180         __release(RCU_BH);
 181         __rcu_read_unlock_bh();
 182 }
 183
 184 /**
 185  * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
 186  *
 187  * Should be used with either
 188  * - synchronize_sched()
 189  * or
 190  * - call_rcu_sched() and rcu_barrier_sched()
 191  * on the write-side to insure proper synchronization.
 192  */
 193 static inline void rcu_read_lock_sched(void)
 194 {
 195         preempt_disable();
 196         __acquire(RCU_SCHED);
 197         rcu_read_acquire();
 198 }
 199
 200 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
 201 static inline notrace void rcu_read_lock_sched_notrace(void)
 202 {
 203         preempt_disable_notrace();
 204         __acquire(RCU_SCHED);
 205 }
 206
 207 /*
 208  * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
 209  *
 210  * See rcu_read_lock_sched for more information.
 211  */
 212 static inline void rcu_read_unlock_sched(void)
 213 {
 214         rcu_read_release();
 215         __release(RCU_SCHED);
 216         preempt_enable();
 217 }
 218
 219 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
 220 static inline notrace void rcu_read_unlock_sched_notrace(void)
 221 {
 222         __release(RCU_SCHED);
 223         preempt_enable_notrace();
 224 }
 225
 226
 227 /**
 228  * rcu_dereference - fetch an RCU-protected pointer in an
 229  * RCU read-side critical section.  This pointer may later
 230  * be safely dereferenced.
 231  *
 232  * Inserts memory barriers on architectures that require them
 233  * (currently only the Alpha), and, more importantly, documents
 234  * exactly which pointers are protected by RCU.
 235  */
 236
 237 #define rcu_dereference(p)     ({ \
 238                                 typeof(p) _________p1 = ACCESS_ONCE(p); \
 239                                 smp_read_barrier_depends(); \
 240                                 (_________p1); \
 241                                 })
 242
 243 /**
 244  * rcu_assign_pointer - assign (publicize) a pointer to a newly
 245  * initialized structure that will be dereferenced by RCU read-side
 246  * critical sections.  Returns the value assigned.
 247  *
 248  * Inserts memory barriers on architectures that require them
 249  * (pretty much all of them other than x86), and also prevents
 250  * the compiler from reordering the code that initializes the
 251  * structure after the pointer assignment.  More importantly, this
 252  * call documents which pointers will be dereferenced by RCU read-side
 253  * code.
 254  */
 255
 256 #define rcu_assign_pointer(p, v) \
 257         ({ \
 258                 if (!__builtin_constant_p(v) || \
 259                     ((v) != NULL)) \
 260                         smp_wmb(); \
 261                 (p) = (v); \
 262         })
 263
 264 /* Infrastructure to implement the synchronize_() primitives. */
 265
 266 struct rcu_synchronize {
 267         struct rcu_head head;
 268         struct completion completion;
 269 };
 270
 271 extern void wakeme_after_rcu(struct rcu_head  *head);
 272
 273 /**
 274  * call_rcu - Queue an RCU callback for invocation after a grace period.
 275  * @head: structure to be used for queueing the RCU updates.
 276  * @func: actual update function to be invoked after the grace period
 277  *
 278  * The update function will be invoked some time after a full grace
 279  * period elapses, in other words after all currently executing RCU
 280  * read-side critical sections have completed.  RCU read-side critical
 281  * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
 282  * and may be nested.
 283  */
 284 extern void call_rcu(struct rcu_head *head,
 285                               void (*func)(struct rcu_head *head));
 286
 287 /**
 288  * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
 289  * @head: structure to be used for queueing the RCU updates.
 290  * @func: actual update function to be invoked after the grace period
 291  *
 292  * The update function will be invoked some time after a full grace
 293  * period elapses, in other words after all currently executing RCU
 294  * read-side critical sections have completed. call_rcu_bh() assumes
 295  * that the read-side critical sections end on completion of a softirq
 296  * handler. This means that read-side critical sections in process
 297  * context must not be interrupted by softirqs. This interface is to be
 298  * used when most of the read-side critical sections are in softirq context.
 299  * RCU read-side critical sections are delimited by :
 300  *  - rcu_read_lock() and  rcu_read_unlock(), if in interrupt context.
 301  *  OR
 302  *  - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
 303  *  These may be nested.
 304  */
 305 extern void call_rcu_bh(struct rcu_head *head,
 306                         void (*func)(struct rcu_head *head));
 307
 308 #endif /* __LINUX_RCUPDATE_H */