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