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 /* Internal to kernel, but needed by rcupreempt.h. */
  55 extern int rcu_scheduler_active;
  56
  57 #if defined(CONFIG_CLASSIC_RCU)
  58 #include <linux/rcuclassic.h>
  59 #elif defined(CONFIG_TREE_RCU)
  60 #include <linux/rcutree.h>
  61 #elif defined(CONFIG_PREEMPT_RCU)
  62 #include <linux/rcupreempt.h>
  63 #else
  64 #error "Unknown RCU implementation specified to kernel configuration"
  65 #endif /* #else #if defined(CONFIG_CLASSIC_RCU) */
  66
  67 #define RCU_HEAD_INIT   { .next = NULL, .func = NULL }
  68 #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
  69 #define INIT_RCU_HEAD(ptr) do { \
  70        (ptr)->next = NULL; (ptr)->func = NULL; \
  71 } while (0)
  72
  73 /**
  74  * rcu_read_lock - mark the beginning of an RCU read-side critical section.
  75  *
  76  * When synchronize_rcu() is invoked on one CPU while other CPUs
  77  * are within RCU read-side critical sections, then the
  78  * synchronize_rcu() is guaranteed to block until after all the other
  79  * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
  80  * on one CPU while other CPUs are within RCU read-side critical
  81  * sections, invocation of the corresponding RCU callback is deferred
  82  * until after the all the other CPUs exit their critical sections.
  83  *
  84  * Note, however, that RCU callbacks are permitted to run concurrently
  85  * with RCU read-side critical sections.  One way that this can happen
  86  * is via the following sequence of events: (1) CPU 0 enters an RCU
  87  * read-side critical section, (2) CPU 1 invokes call_rcu() to register
  88  * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
  89  * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
  90  * callback is invoked.  This is legal, because the RCU read-side critical
  91  * section that was running concurrently with the call_rcu() (and which
  92  * therefore might be referencing something that the corresponding RCU
  93  * callback would free up) has completed before the corresponding
  94  * RCU callback is invoked.
  95  *
  96  * RCU read-side critical sections may be nested.  Any deferred actions
  97  * will be deferred until the outermost RCU read-side critical section
  98  * completes.
  99  *
 100  * It is illegal to block while in an RCU read-side critical section.
 101  */
 102 #define rcu_read_lock() __rcu_read_lock()
 103
 104 /**
 105  * rcu_read_unlock - marks the end of an RCU read-side critical section.
 106  *
 107  * See rcu_read_lock() for more information.
 108  */
 109
 110 /*
 111  * So where is rcu_write_lock()?  It does not exist, as there is no
 112  * way for writers to lock out RCU readers.  This is a feature, not
 113  * a bug -- this property is what provides RCU's performance benefits.
 114  * Of course, writers must coordinate with each other.  The normal
 115  * spinlock primitives work well for this, but any other technique may be
 116  * used as well.  RCU does not care how the writers keep out of each
 117  * others' way, as long as they do so.
 118  */
 119 #define rcu_read_unlock() __rcu_read_unlock()
 120
 121 /**
 122  * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
 123  *
 124  * This is equivalent of rcu_read_lock(), but to be used when updates
 125  * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
 126  * consider completion of a softirq handler to be a quiescent state,
 127  * a process in RCU read-side critical section must be protected by
 128  * disabling softirqs. Read-side critical sections in interrupt context
 129  * can use just rcu_read_lock().
 130  *
 131  */
 132 #define rcu_read_lock_bh() __rcu_read_lock_bh()
 133
 134 /*
 135  * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
 136  *
 137  * See rcu_read_lock_bh() for more information.
 138  */
 139 #define rcu_read_unlock_bh() __rcu_read_unlock_bh()
 140
 141 /**
 142  * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
 143  *
 144  * Should be used with either
 145  * - synchronize_sched()
 146  * or
 147  * - call_rcu_sched() and rcu_barrier_sched()
 148  * on the write-side to insure proper synchronization.
 149  */
 150 #define rcu_read_lock_sched() preempt_disable()
 151 #define rcu_read_lock_sched_notrace() preempt_disable_notrace()
 152
 153 /*
 154  * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
 155  *
 156  * See rcu_read_lock_sched for more information.
 157  */
 158 #define rcu_read_unlock_sched() preempt_enable()
 159 #define rcu_read_unlock_sched_notrace() preempt_enable_notrace()
 160
 161
 162
 163 /**
 164  * rcu_dereference - fetch an RCU-protected pointer in an
 165  * RCU read-side critical section.  This pointer may later
 166  * be safely dereferenced.
 167  *
 168  * Inserts memory barriers on architectures that require them
 169  * (currently only the Alpha), and, more importantly, documents
 170  * exactly which pointers are protected by RCU.
 171  */
 172
 173 #define rcu_dereference(p)     ({ \
 174                                 typeof(p) _________p1 = ACCESS_ONCE(p); \
 175                                 smp_read_barrier_depends(); \
 176                                 (_________p1); \
 177                                 })
 178
 179 /**
 180  * rcu_assign_pointer - assign (publicize) a pointer to a newly
 181  * initialized structure that will be dereferenced by RCU read-side
 182  * critical sections.  Returns the value assigned.
 183  *
 184  * Inserts memory barriers on architectures that require them
 185  * (pretty much all of them other than x86), and also prevents
 186  * the compiler from reordering the code that initializes the
 187  * structure after the pointer assignment.  More importantly, this
 188  * call documents which pointers will be dereferenced by RCU read-side
 189  * code.
 190  */
 191
 192 #define rcu_assign_pointer(p, v) \
 193         ({ \
 194                 if (!__builtin_constant_p(v) || \
 195                     ((v) != NULL)) \
 196                         smp_wmb(); \
 197                 (p) = (v); \
 198         })
 199
 200 /* Infrastructure to implement the synchronize_() primitives. */
 201
 202 struct rcu_synchronize {
 203         struct rcu_head head;
 204         struct completion completion;
 205 };
 206
 207 extern void wakeme_after_rcu(struct rcu_head  *head);
 208
 209 /**
 210  * synchronize_sched - block until all CPUs have exited any non-preemptive
 211  * kernel code sequences.
 212  *
 213  * This means that all preempt_disable code sequences, including NMI and
 214  * hardware-interrupt handlers, in progress on entry will have completed
 215  * before this primitive returns.  However, this does not guarantee that
 216  * softirq handlers will have completed, since in some kernels, these
 217  * handlers can run in process context, and can block.
 218  *
 219  * This primitive provides the guarantees made by the (now removed)
 220  * synchronize_kernel() API.  In contrast, synchronize_rcu() only
 221  * guarantees that rcu_read_lock() sections will have completed.
 222  * In "classic RCU", these two guarantees happen to be one and
 223  * the same, but can differ in realtime RCU implementations.
 224  */
 225 #define synchronize_sched() __synchronize_sched()
 226
 227 /**
 228  * call_rcu - Queue an RCU callback for invocation after a grace period.
 229  * @head: structure to be used for queueing the RCU updates.
 230  * @func: actual update function to be invoked after the grace period
 231  *
 232  * The update function will be invoked some time after a full grace
 233  * period elapses, in other words after all currently executing RCU
 234  * read-side critical sections have completed.  RCU read-side critical
 235  * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
 236  * and may be nested.
 237  */
 238 extern void call_rcu(struct rcu_head *head,
 239                               void (*func)(struct rcu_head *head));
 240
 241 /**
 242  * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
 243  * @head: structure to be used for queueing the RCU updates.
 244  * @func: actual update function to be invoked after the grace period
 245  *
 246  * The update function will be invoked some time after a full grace
 247  * period elapses, in other words after all currently executing RCU
 248  * read-side critical sections have completed. call_rcu_bh() assumes
 249  * that the read-side critical sections end on completion of a softirq
 250  * handler. This means that read-side critical sections in process
 251  * context must not be interrupted by softirqs. This interface is to be
 252  * used when most of the read-side critical sections are in softirq context.
 253  * RCU read-side critical sections are delimited by :
 254  *  - rcu_read_lock() and  rcu_read_unlock(), if in interrupt context.
 255  *  OR
 256  *  - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
 257  *  These may be nested.
 258  */
 259 extern void call_rcu_bh(struct rcu_head *head,
 260                         void (*func)(struct rcu_head *head));
 261
 262 /* Exported common interfaces */
 263 extern void synchronize_rcu(void);
 264 extern void rcu_barrier(void);
 265 extern void rcu_barrier_bh(void);
 266 extern void rcu_barrier_sched(void);
 267
 268 /* Internal to kernel */
 269 extern void rcu_init(void);
 270 extern void rcu_scheduler_starting(void);
 271 extern int rcu_needs_cpu(int cpu);
 272
 273 #endif /* __LINUX_RCUPDATE_H */