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 (C) 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 #ifdef __KERNEL__
  37
  38 #include <linux/cache.h>
  39 #include <linux/spinlock.h>
  40 #include <linux/threads.h>
  41 #include <linux/percpu.h>
  42 #include <linux/cpumask.h>
  43 #include <linux/seqlock.h>
  44 #include <linux/lockdep.h>
  45
  46 /**
  47  * struct rcu_head - callback structure for use with RCU
  48  * @next: next update requests in a list
  49  * @func: actual update function to call after the grace period.
  50  */
  51 struct rcu_head {
  52         struct rcu_head *next;
  53         void (*func)(struct rcu_head *head);
  54 };
  55
  56 #define RCU_HEAD_INIT   { .next = NULL, .func = NULL }
  57 #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
  58 #define INIT_RCU_HEAD(ptr) do { \
  59        (ptr)->next = NULL; (ptr)->func = NULL; \
  60 } while (0)
  61
  62
  63
  64 /* Global control variables for rcupdate callback mechanism. */
  65 struct rcu_ctrlblk {
  66         long    cur;            /* Current batch number.                      */
  67         long    completed;      /* Number of the last completed batch         */
  68         int     next_pending;   /* Is the next batch already waiting?         */
  69
  70         int     signaled;
  71
  72         spinlock_t      lock    ____cacheline_internodealigned_in_smp;
  73         cpumask_t       cpumask; /* CPUs that need to switch in order    */
  74                                  /* for current batch to proceed.        */
  75 } ____cacheline_internodealigned_in_smp;
  76
  77 /* Is batch a before batch b ? */
  78 static inline int rcu_batch_before(long a, long b)
  79 {
  80         return (a - b) < 0;
  81 }
  82
  83 /* Is batch a after batch b ? */
  84 static inline int rcu_batch_after(long a, long b)
  85 {
  86         return (a - b) > 0;
  87 }
  88
  89 /*
  90  * Per-CPU data for Read-Copy UPdate.
  91  * nxtlist - new callbacks are added here
  92  * curlist - current batch for which quiescent cycle started if any
  93  */
  94 struct rcu_data {
  95         /* 1) quiescent state handling : */
  96         long            quiescbatch;     /* Batch # for grace period */
  97         int             passed_quiesc;   /* User-mode/idle loop etc. */
  98         int             qs_pending;      /* core waits for quiesc state */
  99
 100         /* 2) batch handling */
 101         long            batch;           /* Batch # for current RCU batch */
 102         struct rcu_head *nxtlist;
 103         struct rcu_head **nxttail;
 104         long            qlen;            /* # of queued callbacks */
 105         struct rcu_head *curlist;
 106         struct rcu_head **curtail;
 107         struct rcu_head *donelist;
 108         struct rcu_head **donetail;
 109         long            blimit;          /* Upper limit on a processed batch */
 110         int cpu;
 111         struct rcu_head barrier;
 112 };
 113
 114 DECLARE_PER_CPU(struct rcu_data, rcu_data);
 115 DECLARE_PER_CPU(struct rcu_data, rcu_bh_data);
 116
 117 /*
 118  * Increment the quiescent state counter.
 119  * The counter is a bit degenerated: We do not need to know
 120  * how many quiescent states passed, just if there was at least
 121  * one since the start of the grace period. Thus just a flag.
 122  */
 123 static inline void rcu_qsctr_inc(int cpu)
 124 {
 125         struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
 126         rdp->passed_quiesc = 1;
 127 }
 128 static inline void rcu_bh_qsctr_inc(int cpu)
 129 {
 130         struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
 131         rdp->passed_quiesc = 1;
 132 }
 133
 134 extern int rcu_pending(int cpu);
 135 extern int rcu_needs_cpu(int cpu);
 136
 137 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 138 extern struct lockdep_map rcu_lock_map;
 139 # define rcu_read_acquire()     lock_acquire(&rcu_lock_map, 0, 0, 2, 1, _THIS_IP_)
 140 # define rcu_read_release()     lock_release(&rcu_lock_map, 1, _THIS_IP_)
 141 #else
 142 # define rcu_read_acquire()     do { } while (0)
 143 # define rcu_read_release()     do { } while (0)
 144 #endif
 145
 146 /**
 147  * rcu_read_lock - mark the beginning of an RCU read-side critical section.
 148  *
 149  * When synchronize_rcu() is invoked on one CPU while other CPUs
 150  * are within RCU read-side critical sections, then the
 151  * synchronize_rcu() is guaranteed to block until after all the other
 152  * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
 153  * on one CPU while other CPUs are within RCU read-side critical
 154  * sections, invocation of the corresponding RCU callback is deferred
 155  * until after the all the other CPUs exit their critical sections.
 156  *
 157  * Note, however, that RCU callbacks are permitted to run concurrently
 158  * with RCU read-side critical sections.  One way that this can happen
 159  * is via the following sequence of events: (1) CPU 0 enters an RCU
 160  * read-side critical section, (2) CPU 1 invokes call_rcu() to register
 161  * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
 162  * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
 163  * callback is invoked.  This is legal, because the RCU read-side critical
 164  * section that was running concurrently with the call_rcu() (and which
 165  * therefore might be referencing something that the corresponding RCU
 166  * callback would free up) has completed before the corresponding
 167  * RCU callback is invoked.
 168  *
 169  * RCU read-side critical sections may be nested.  Any deferred actions
 170  * will be deferred until the outermost RCU read-side critical section
 171  * completes.
 172  *
 173  * It is illegal to block while in an RCU read-side critical section.
 174  */
 175 #define rcu_read_lock() \
 176         do { \
 177                 preempt_disable(); \
 178                 __acquire(RCU); \
 179                 rcu_read_acquire(); \
 180         } while(0)
 181
 182 /**
 183  * rcu_read_unlock - marks the end of an RCU read-side critical section.
 184  *
 185  * See rcu_read_lock() for more information.
 186  */
 187 #define rcu_read_unlock() \
 188         do { \
 189                 rcu_read_release(); \
 190                 __release(RCU); \
 191                 preempt_enable(); \
 192         } while(0)
 193
 194 /*
 195  * So where is rcu_write_lock()?  It does not exist, as there is no
 196  * way for writers to lock out RCU readers.  This is a feature, not
 197  * a bug -- this property is what provides RCU's performance benefits.
 198  * Of course, writers must coordinate with each other.  The normal
 199  * spinlock primitives work well for this, but any other technique may be
 200  * used as well.  RCU does not care how the writers keep out of each
 201  * others' way, as long as they do so.
 202  */
 203
 204 /**
 205  * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
 206  *
 207  * This is equivalent of rcu_read_lock(), but to be used when updates
 208  * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
 209  * consider completion of a softirq handler to be a quiescent state,
 210  * a process in RCU read-side critical section must be protected by
 211  * disabling softirqs. Read-side critical sections in interrupt context
 212  * can use just rcu_read_lock().
 213  *
 214  */
 215 #define rcu_read_lock_bh() \
 216         do { \
 217                 local_bh_disable(); \
 218                 __acquire(RCU_BH); \
 219                 rcu_read_acquire(); \
 220         } while(0)
 221
 222 /*
 223  * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
 224  *
 225  * See rcu_read_lock_bh() for more information.
 226  */
 227 #define rcu_read_unlock_bh() \
 228         do { \
 229                 rcu_read_release(); \
 230                 __release(RCU_BH); \
 231                 local_bh_enable(); \
 232         } while(0)
 233
 234 /**
 235  * rcu_dereference - fetch an RCU-protected pointer in an
 236  * RCU read-side critical section.  This pointer may later
 237  * be safely dereferenced.
 238  *
 239  * Inserts memory barriers on architectures that require them
 240  * (currently only the Alpha), and, more importantly, documents
 241  * exactly which pointers are protected by RCU.
 242  */
 243
 244 #define rcu_dereference(p)     ({ \
 245                                 typeof(p) _________p1 = p; \
 246                                 smp_read_barrier_depends(); \
 247                                 (_________p1); \
 248                                 })
 249
 250 /**
 251  * rcu_assign_pointer - assign (publicize) a pointer to a newly
 252  * initialized structure that will be dereferenced by RCU read-side
 253  * critical sections.  Returns the value assigned.
 254  *
 255  * Inserts memory barriers on architectures that require them
 256  * (pretty much all of them other than x86), and also prevents
 257  * the compiler from reordering the code that initializes the
 258  * structure after the pointer assignment.  More importantly, this
 259  * call documents which pointers will be dereferenced by RCU read-side
 260  * code.
 261  */
 262
 263 #define rcu_assign_pointer(p, v)        ({ \
 264                                                 smp_wmb(); \
 265                                                 (p) = (v); \
 266                                         })
 267
 268 /**
 269  * synchronize_sched - block until all CPUs have exited any non-preemptive
 270  * kernel code sequences.
 271  *
 272  * This means that all preempt_disable code sequences, including NMI and
 273  * hardware-interrupt handlers, in progress on entry will have completed
 274  * before this primitive returns.  However, this does not guarantee that
 275  * softirq handlers will have completed, since in some kernels, these
 276  * handlers can run in process context, and can block.
 277  *
 278  * This primitive provides the guarantees made by the (now removed)
 279  * synchronize_kernel() API.  In contrast, synchronize_rcu() only
 280  * guarantees that rcu_read_lock() sections will have completed.
 281  * In "classic RCU", these two guarantees happen to be one and
 282  * the same, but can differ in realtime RCU implementations.
 283  */
 284 #define synchronize_sched() synchronize_rcu()
 285
 286 extern void rcu_init(void);
 287 extern void rcu_check_callbacks(int cpu, int user);
 288 extern void rcu_restart_cpu(int cpu);
 289 extern long rcu_batches_completed(void);
 290 extern long rcu_batches_completed_bh(void);
 291
 292 /* Exported interfaces */
 293 extern void FASTCALL(call_rcu(struct rcu_head *head,
 294                                 void (*func)(struct rcu_head *head)));
 295 extern void FASTCALL(call_rcu_bh(struct rcu_head *head,
 296                                 void (*func)(struct rcu_head *head)));
 297 extern void synchronize_rcu(void);
 298 extern void rcu_barrier(void);
 299
 300 #endif /* __KERNEL__ */
 301 #endif /* __LINUX_RCUPDATE_H */