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(void);
  56 extern void synchronize_rcu_bh(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 void rcu_scheduler_starting(void);
  66 extern int rcu_needs_cpu(int cpu);
  67 extern int rcu_scheduler_active;
  68
  69 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
  70 #include <linux/rcutree.h>
  71 #else
  72 #error "Unknown RCU implementation specified to kernel configuration"
  73 #endif
  74
  75 #define RCU_HEAD_INIT   { .next = NULL, .func = NULL }
  76 #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
  77 #define INIT_RCU_HEAD(ptr) do { \
  78        (ptr)->next = NULL; (ptr)->func = NULL; \
  79 } while (0)
  80
  81 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  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 #else
  87 # define rcu_read_acquire()     do { } while (0)
  88 # define rcu_read_release()     do { } while (0)
  89 #endif
  90
  91 /**
  92  * rcu_read_lock - mark the beginning of an RCU read-side critical section.
  93  *
  94  * When synchronize_rcu() is invoked on one CPU while other CPUs
  95  * are within RCU read-side critical sections, then the
  96  * synchronize_rcu() is guaranteed to block until after all the other
  97  * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
  98  * on one CPU while other CPUs are within RCU read-side critical
  99  * sections, invocation of the corresponding RCU callback is deferred
 100  * until after the all the other CPUs exit their critical sections.
 101  *
 102  * Note, however, that RCU callbacks are permitted to run concurrently
 103  * with RCU read-side critical sections.  One way that this can happen
 104  * is via the following sequence of events: (1) CPU 0 enters an RCU
 105  * read-side critical section, (2) CPU 1 invokes call_rcu() to register
 106  * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
 107  * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
 108  * callback is invoked.  This is legal, because the RCU read-side critical
 109  * section that was running concurrently with the call_rcu() (and which
 110  * therefore might be referencing something that the corresponding RCU
 111  * callback would free up) has completed before the corresponding
 112  * RCU callback is invoked.
 113  *
 114  * RCU read-side critical sections may be nested.  Any deferred actions
 115  * will be deferred until the outermost RCU read-side critical section
 116  * completes.
 117  *
 118  * It is illegal to block while in an RCU read-side critical section.
 119  */
 120 static inline void rcu_read_lock(void)
 121 {
 122         __rcu_read_lock();
 123         __acquire(RCU);
 124         rcu_read_acquire();
 125 }
 126
 127 /**
 128  * rcu_read_unlock - marks the end of an RCU read-side critical section.
 129  *
 130  * See rcu_read_lock() for more information.
 131  */
 132
 133 /*
 134  * So where is rcu_write_lock()?  It does not exist, as there is no
 135  * way for writers to lock out RCU readers.  This is a feature, not
 136  * a bug -- this property is what provides RCU's performance benefits.
 137  * Of course, writers must coordinate with each other.  The normal
 138  * spinlock primitives work well for this, but any other technique may be
 139  * used as well.  RCU does not care how the writers keep out of each
 140  * others' way, as long as they do so.
 141  */
 142 static inline void rcu_read_unlock(void)
 143 {
 144         rcu_read_release();
 145         __release(RCU);
 146         __rcu_read_unlock();
 147 }
 148
 149 /**
 150  * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
 151  *
 152  * This is equivalent of rcu_read_lock(), but to be used when updates
 153  * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
 154  * consider completion of a softirq handler to be a quiescent state,
 155  * a process in RCU read-side critical section must be protected by
 156  * disabling softirqs. Read-side critical sections in interrupt context
 157  * can use just rcu_read_lock().
 158  *
 159  */
 160 static inline void rcu_read_lock_bh(void)
 161 {
 162         __rcu_read_lock_bh();
 163         __acquire(RCU_BH);
 164         rcu_read_acquire();
 165 }
 166
 167 /*
 168  * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
 169  *
 170  * See rcu_read_lock_bh() for more information.
 171  */
 172 static inline void rcu_read_unlock_bh(void)
 173 {
 174         rcu_read_release();
 175         __release(RCU_BH);
 176         __rcu_read_unlock_bh();
 177 }
 178
 179 /**
 180  * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
 181  *
 182  * Should be used with either
 183  * - synchronize_sched()
 184  * or
 185  * - call_rcu_sched() and rcu_barrier_sched()
 186  * on the write-side to insure proper synchronization.
 187  */
 188 static inline void rcu_read_lock_sched(void)
 189 {
 190         preempt_disable();
 191         __acquire(RCU_SCHED);
 192         rcu_read_acquire();
 193 }
 194 static inline notrace void rcu_read_lock_sched_notrace(void)
 195 {
 196         preempt_disable_notrace();
 197         __acquire(RCU_SCHED);
 198 }
 199
 200 /*
 201  * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
 202  *
 203  * See rcu_read_lock_sched for more information.
 204  */
 205 static inline void rcu_read_unlock_sched(void)
 206 {
 207         rcu_read_release();
 208         __release(RCU_SCHED);
 209         preempt_enable();
 210 }
 211 static inline notrace void rcu_read_unlock_sched_notrace(void)
 212 {
 213         __release(RCU_SCHED);
 214         preempt_enable_notrace();
 215 }
 216
 217
 218 /**
 219  * rcu_dereference - fetch an RCU-protected pointer in an
 220  * RCU read-side critical section.  This pointer may later
 221  * be safely dereferenced.
 222  *
 223  * Inserts memory barriers on architectures that require them
 224  * (currently only the Alpha), and, more importantly, documents
 225  * exactly which pointers are protected by RCU.
 226  */
 227
 228 #define rcu_dereference(p)     ({ \
 229                                 typeof(p) _________p1 = ACCESS_ONCE(p); \
 230                                 smp_read_barrier_depends(); \
 231                                 (_________p1); \
 232                                 })
 233
 234 /**
 235  * rcu_assign_pointer - assign (publicize) a pointer to a newly
 236  * initialized structure that will be dereferenced by RCU read-side
 237  * critical sections.  Returns the value assigned.
 238  *
 239  * Inserts memory barriers on architectures that require them
 240  * (pretty much all of them other than x86), and also prevents
 241  * the compiler from reordering the code that initializes the
 242  * structure after the pointer assignment.  More importantly, this
 243  * call documents which pointers will be dereferenced by RCU read-side
 244  * code.
 245  */
 246
 247 #define rcu_assign_pointer(p, v) \
 248         ({ \
 249                 if (!__builtin_constant_p(v) || \
 250                     ((v) != NULL)) \
 251                         smp_wmb(); \
 252                 (p) = (v); \
 253         })
 254
 255 /* Infrastructure to implement the synchronize_() primitives. */
 256
 257 struct rcu_synchronize {
 258         struct rcu_head head;
 259         struct completion completion;
 260 };
 261
 262 extern void wakeme_after_rcu(struct rcu_head  *head);
 263
 264 /**
 265  * synchronize_sched - block until all CPUs have exited any non-preemptive
 266  * kernel code sequences.
 267  *
 268  * This means that all preempt_disable code sequences, including NMI and
 269  * hardware-interrupt handlers, in progress on entry will have completed
 270  * before this primitive returns.  However, this does not guarantee that
 271  * softirq handlers will have completed, since in some kernels, these
 272  * handlers can run in process context, and can block.
 273  *
 274  * This primitive provides the guarantees made by the (now removed)
 275  * synchronize_kernel() API.  In contrast, synchronize_rcu() only
 276  * guarantees that rcu_read_lock() sections will have completed.
 277  * In "classic RCU", these two guarantees happen to be one and
 278  * the same, but can differ in realtime RCU implementations.
 279  */
 280 #define synchronize_sched() __synchronize_sched()
 281
 282 /**
 283  * call_rcu - Queue an RCU callback for invocation after a grace period.
 284  * @head: structure to be used for queueing the RCU updates.
 285  * @func: actual update function to be invoked after the grace period
 286  *
 287  * The update function will be invoked some time after a full grace
 288  * period elapses, in other words after all currently executing RCU
 289  * read-side critical sections have completed.  RCU read-side critical
 290  * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
 291  * and may be nested.
 292  */
 293 extern void call_rcu(struct rcu_head *head,
 294                               void (*func)(struct rcu_head *head));
 295
 296 /**
 297  * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
 298  * @head: structure to be used for queueing the RCU updates.
 299  * @func: actual update function to be invoked after the grace period
 300  *
 301  * The update function will be invoked some time after a full grace
 302  * period elapses, in other words after all currently executing RCU
 303  * read-side critical sections have completed. call_rcu_bh() assumes
 304  * that the read-side critical sections end on completion of a softirq
 305  * handler. This means that read-side critical sections in process
 306  * context must not be interrupted by softirqs. This interface is to be
 307  * used when most of the read-side critical sections are in softirq context.
 308  * RCU read-side critical sections are delimited by :
 309  *  - rcu_read_lock() and  rcu_read_unlock(), if in interrupt context.
 310  *  OR
 311  *  - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
 312  *  These may be nested.
 313  */
 314 extern void call_rcu_bh(struct rcu_head *head,
 315                         void (*func)(struct rcu_head *head));
 316
 317 #endif /* __LINUX_RCUPDATE_H */