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/percpu.h>
  40 #include <linux/cpumask.h>
  41 #include <linux/seqlock.h>
  42 #include <linux/lockdep.h>
  43 #include <linux/completion.h>
  44
  45 /**
  46  * struct rcu_head - callback structure for use with RCU
  47  * @next: next update requests in a list
  48  * @func: actual update function to call after the grace period.
  49  */
  50 struct rcu_head {
  51         struct rcu_head *next;
  52         void (*func)(struct rcu_head *head);
  53 };
  54
  55 #ifdef CONFIG_CLASSIC_RCU
  56 #include <linux/rcuclassic.h>
  57 #else /* #ifdef CONFIG_CLASSIC_RCU */
  58 #include <linux/rcupreempt.h>
  59 #endif /* #else #ifdef CONFIG_CLASSIC_RCU */
  60
  61 #define RCU_HEAD_INIT   { .next = NULL, .func = NULL }
  62 #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
  63 #define INIT_RCU_HEAD(ptr) do { \
  64        (ptr)->next = NULL; (ptr)->func = NULL; \
  65 } while (0)
  66
  67 /**
  68  * rcu_read_lock - mark the beginning of an RCU read-side critical section.
  69  *
  70  * When synchronize_rcu() is invoked on one CPU while other CPUs
  71  * are within RCU read-side critical sections, then the
  72  * synchronize_rcu() is guaranteed to block until after all the other
  73  * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
  74  * on one CPU while other CPUs are within RCU read-side critical
  75  * sections, invocation of the corresponding RCU callback is deferred
  76  * until after the all the other CPUs exit their critical sections.
  77  *
  78  * Note, however, that RCU callbacks are permitted to run concurrently
  79  * with RCU read-side critical sections.  One way that this can happen
  80  * is via the following sequence of events: (1) CPU 0 enters an RCU
  81  * read-side critical section, (2) CPU 1 invokes call_rcu() to register
  82  * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
  83  * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
  84  * callback is invoked.  This is legal, because the RCU read-side critical
  85  * section that was running concurrently with the call_rcu() (and which
  86  * therefore might be referencing something that the corresponding RCU
  87  * callback would free up) has completed before the corresponding
  88  * RCU callback is invoked.
  89  *
  90  * RCU read-side critical sections may be nested.  Any deferred actions
  91  * will be deferred until the outermost RCU read-side critical section
  92  * completes.
  93  *
  94  * It is illegal to block while in an RCU read-side critical section.
  95  */
  96 #define rcu_read_lock() __rcu_read_lock()
  97
  98 /**
  99  * rcu_read_unlock - marks the end of an RCU read-side critical section.
 100  *
 101  * See rcu_read_lock() for more information.
 102  */
 103
 104 /*
 105  * So where is rcu_write_lock()?  It does not exist, as there is no
 106  * way for writers to lock out RCU readers.  This is a feature, not
 107  * a bug -- this property is what provides RCU's performance benefits.
 108  * Of course, writers must coordinate with each other.  The normal
 109  * spinlock primitives work well for this, but any other technique may be
 110  * used as well.  RCU does not care how the writers keep out of each
 111  * others' way, as long as they do so.
 112  */
 113 #define rcu_read_unlock() __rcu_read_unlock()
 114
 115 /**
 116  * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
 117  *
 118  * This is equivalent of rcu_read_lock(), but to be used when updates
 119  * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
 120  * consider completion of a softirq handler to be a quiescent state,
 121  * a process in RCU read-side critical section must be protected by
 122  * disabling softirqs. Read-side critical sections in interrupt context
 123  * can use just rcu_read_lock().
 124  *
 125  */
 126 #define rcu_read_lock_bh() __rcu_read_lock_bh()
 127
 128 /*
 129  * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
 130  *
 131  * See rcu_read_lock_bh() for more information.
 132  */
 133 #define rcu_read_unlock_bh() __rcu_read_unlock_bh()
 134
 135 /**
 136  * rcu_dereference - fetch an RCU-protected pointer in an
 137  * RCU read-side critical section.  This pointer may later
 138  * be safely dereferenced.
 139  *
 140  * Inserts memory barriers on architectures that require them
 141  * (currently only the Alpha), and, more importantly, documents
 142  * exactly which pointers are protected by RCU.
 143  */
 144
 145 #define rcu_dereference(p)     ({ \
 146                                 typeof(p) _________p1 = ACCESS_ONCE(p); \
 147                                 smp_read_barrier_depends(); \
 148                                 (_________p1); \
 149                                 })
 150
 151 /**
 152  * rcu_assign_pointer - assign (publicize) a pointer to a newly
 153  * initialized structure that will be dereferenced by RCU read-side
 154  * critical sections.  Returns the value assigned.
 155  *
 156  * Inserts memory barriers on architectures that require them
 157  * (pretty much all of them other than x86), and also prevents
 158  * the compiler from reordering the code that initializes the
 159  * structure after the pointer assignment.  More importantly, this
 160  * call documents which pointers will be dereferenced by RCU read-side
 161  * code.
 162  */
 163
 164 #define rcu_assign_pointer(p, v) \
 165         ({ \
 166                 if (!__builtin_constant_p(v) || \
 167                     ((v) != NULL)) \
 168                         smp_wmb(); \
 169                 (p) = (v); \
 170         })
 171
 172 /* Infrastructure to implement the synchronize_() primitives. */
 173
 174 struct rcu_synchronize {
 175         struct rcu_head head;
 176         struct completion completion;
 177 };
 178
 179 extern void wakeme_after_rcu(struct rcu_head  *head);
 180
 181 #define synchronize_rcu_xxx(name, func) \
 182 void name(void) \
 183 { \
 184         struct rcu_synchronize rcu; \
 185         \
 186         init_completion(&rcu.completion); \
 187         /* Will wake me after RCU finished. */ \
 188         func(&rcu.head, wakeme_after_rcu); \
 189         /* Wait for it. */ \
 190         wait_for_completion(&rcu.completion); \
 191 }
 192
 193 /**
 194  * synchronize_sched - block until all CPUs have exited any non-preemptive
 195  * kernel code sequences.
 196  *
 197  * This means that all preempt_disable code sequences, including NMI and
 198  * hardware-interrupt handlers, in progress on entry will have completed
 199  * before this primitive returns.  However, this does not guarantee that
 200  * softirq handlers will have completed, since in some kernels, these
 201  * handlers can run in process context, and can block.
 202  *
 203  * This primitive provides the guarantees made by the (now removed)
 204  * synchronize_kernel() API.  In contrast, synchronize_rcu() only
 205  * guarantees that rcu_read_lock() sections will have completed.
 206  * In "classic RCU", these two guarantees happen to be one and
 207  * the same, but can differ in realtime RCU implementations.
 208  */
 209 #define synchronize_sched() __synchronize_sched()
 210
 211 /**
 212  * call_rcu - Queue an RCU callback for invocation after a grace period.
 213  * @head: structure to be used for queueing the RCU updates.
 214  * @func: actual update function to be invoked after the grace period
 215  *
 216  * The update function will be invoked some time after a full grace
 217  * period elapses, in other words after all currently executing RCU
 218  * read-side critical sections have completed.  RCU read-side critical
 219  * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
 220  * and may be nested.
 221  */
 222 extern void call_rcu(struct rcu_head *head,
 223                               void (*func)(struct rcu_head *head));
 224
 225 /**
 226  * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
 227  * @head: structure to be used for queueing the RCU updates.
 228  * @func: actual update function to be invoked after the grace period
 229  *
 230  * The update function will be invoked some time after a full grace
 231  * period elapses, in other words after all currently executing RCU
 232  * read-side critical sections have completed. call_rcu_bh() assumes
 233  * that the read-side critical sections end on completion of a softirq
 234  * handler. This means that read-side critical sections in process
 235  * context must not be interrupted by softirqs. This interface is to be
 236  * used when most of the read-side critical sections are in softirq context.
 237  * RCU read-side critical sections are delimited by :
 238  *  - rcu_read_lock() and  rcu_read_unlock(), if in interrupt context.
 239  *  OR
 240  *  - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
 241  *  These may be nested.
 242  */
 243 extern void call_rcu_bh(struct rcu_head *head,
 244                         void (*func)(struct rcu_head *head));
 245
 246 /* Exported common interfaces */
 247 extern void synchronize_rcu(void);
 248 extern void rcu_barrier(void);
 249 extern void rcu_barrier_bh(void);
 250 extern void rcu_barrier_sched(void);
 251
 252 /* Internal to kernel */
 253 extern void rcu_init(void);
 254 extern int rcu_needs_cpu(int cpu);
 255
 256 #endif /* __LINUX_RCUPDATE_H */