LXR linux-bk/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 <paul.mckenney@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
  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 */
  50struct rcu_head {
  51        struct rcu_head *next;
  52        void (*func)(struct rcu_head *head);
  53};
  54
  55#define RCU_HEAD_INIT(head) { .next = NULL, .func = NULL }
  56#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT(head)
  57#define INIT_RCU_HEAD(ptr) do { \
  58       (ptr)->next = NULL; (ptr)->func = NULL; \
  59} while (0)
  60
  61
  62
  63/* Global control variables for rcupdate callback mechanism. */
  64struct rcu_ctrlblk {
  65        long    cur;            /* Current batch number.                      */
  66        long    completed;      /* Number of the last completed batch         */
  67        int     next_pending;   /* Is the next batch already waiting?         */
  68        seqcount_t lock;        /* For atomic reads of cur and next_pending.  */
  69} ____cacheline_maxaligned_in_smp;
  70
  71/* Is batch a before batch b ? */
  72static inline int rcu_batch_before(long a, long b)
  73{
  74        return (a - b) < 0;
  75}
  76
  77/* Is batch a after batch b ? */
  78static inline int rcu_batch_after(long a, long b)
  79{
  80        return (a - b) > 0;
  81}
  82
  83/*
  84 * Per-CPU data for Read-Copy UPdate.
  85 * nxtlist - new callbacks are added here
  86 * curlist - current batch for which quiescent cycle started if any
  87 */
  88struct rcu_data {
  89        /* 1) quiescent state handling : */
  90        long            quiescbatch;     /* Batch # for grace period */
  91        long            qsctr;           /* User-mode/idle loop etc. */
  92        long            last_qsctr;      /* value of qsctr at beginning */
  93                                         /* of rcu grace period */
  94        int             qs_pending;      /* core waits for quiesc state */
  95
  96        /* 2) batch handling */
  97        long            batch;           /* Batch # for current RCU batch */
  98        struct rcu_head *nxtlist;
  99        struct rcu_head **nxttail;
 100        struct rcu_head *curlist;
 101};
 102
 103DECLARE_PER_CPU(struct rcu_data, rcu_data);
 104extern struct rcu_ctrlblk rcu_ctrlblk;
 105
 106#define RCU_quiescbatch(cpu)    (per_cpu(rcu_data, (cpu)).quiescbatch)
 107#define RCU_qsctr(cpu)          (per_cpu(rcu_data, (cpu)).qsctr)
 108#define RCU_last_qsctr(cpu)     (per_cpu(rcu_data, (cpu)).last_qsctr)
 109#define RCU_qs_pending(cpu)     (per_cpu(rcu_data, (cpu)).qs_pending)
 110#define RCU_batch(cpu)          (per_cpu(rcu_data, (cpu)).batch)
 111#define RCU_nxtlist(cpu)        (per_cpu(rcu_data, (cpu)).nxtlist)
 112#define RCU_curlist(cpu)        (per_cpu(rcu_data, (cpu)).curlist)
 113#define RCU_nxttail(cpu)        (per_cpu(rcu_data, (cpu)).nxttail)
 114
 115static inline int rcu_pending(int cpu) 
 116{
 117        /* This cpu has pending rcu entries and the grace period
 118         * for them has completed.
 119         */
 120        if (RCU_curlist(cpu) &&
 121                  !rcu_batch_before(rcu_ctrlblk.completed,RCU_batch(cpu)))
 122                return 1;
 123
 124        /* This cpu has no pending entries, but there are new entries */
 125        if (!RCU_curlist(cpu) && RCU_nxtlist(cpu))
 126                return 1;
 127
 128        /* The rcu core waits for a quiescent state from the cpu */
 129        if (RCU_quiescbatch(cpu) != rcu_ctrlblk.cur || RCU_qs_pending(cpu))
 130                return 1;
 131
 132        /* nothing to do */
 133        return 0;
 134}
 135
 136#define rcu_read_lock()         preempt_disable()
 137#define rcu_read_unlock()       preempt_enable()
 138
 139extern void rcu_init(void);
 140extern void rcu_check_callbacks(int cpu, int user);
 141extern void rcu_restart_cpu(int cpu);
 142
 143/* Exported interfaces */
 144extern void FASTCALL(call_rcu(struct rcu_head *head, 
 145                                void (*func)(struct rcu_head *head)));
 146extern void synchronize_kernel(void);
 147
 148#endif /* __KERNEL__ */
 149#endif /* __LINUX_RCUPDATE_H */
 150