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/*
* Read-Copy Update mechanism for mutual exclusion
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
* Copyright (C) IBM Corporation, 2001
*
* Author: Dipankar Sarma <dipankar@in.ibm.com>
*
* Based on the original work by Paul McKenney <paul.mckenney@us.ibm.com>
* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
* Papers:
* http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
* http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
*
* For detailed explanation of Read-Copy Update mechanism see -
* http://lse.sourceforge.net/locking/rcupdate.html
*
*/
#ifndef __LINUX_RCUPDATE_H
#define __LINUX_RCUPDATE_H
#ifdef __KERNEL__
#include <linux/cache.h>
#include <linux/spinlock.h>
#include <linux/threads.h>
#include <linux/percpu.h>
#include <linux/cpumask.h>
#include <linux/seqlock.h>
/**
* struct rcu_head - callback structure for use with RCU
* @next: next update requests in a list
* @func: actual update function to call after the grace period.
*/
struct rcu_head {
struct rcu_head *next;
void (*func)(struct rcu_head *head);
};
#define RCU_HEAD_INIT(head) { .next = NULL, .func = NULL }
#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT(head)
#define INIT_RCU_HEAD(ptr) do { \
(ptr)->next = NULL; (ptr)->func = NULL; \
} while (0)
/* Global control variables for rcupdate callback mechanism. */
struct rcu_ctrlblk {
long cur; /* Current batch number. */
long completed; /* Number of the last completed batch */
int next_pending; /* Is the next batch already waiting? */
seqcount_t lock; /* For atomic reads of cur and next_pending. */
} ____cacheline_maxaligned_in_smp;
/* Is batch a before batch b ? */
static inline int rcu_batch_before(long a, long b)
{
return (a - b) < 0;
}
/* Is batch a after batch b ? */
static inline int rcu_batch_after(long a, long b)
{
return (a - b) > 0;
}
/*
* Per-CPU data for Read-Copy UPdate.
* nxtlist - new callbacks are added here
* curlist - current batch for which quiescent cycle started if any
*/
struct rcu_data {
/* 1) quiescent state handling : */
long quiescbatch; /* Batch # for grace period */
long qsctr; /* User-mode/idle loop etc. */
long last_qsctr; /* value of qsctr at beginning */
/* of rcu grace period */
int qs_pending; /* core waits for quiesc state */
/* 2) batch handling */
long batch; /* Batch # for current RCU batch */
struct rcu_head *nxtlist;
struct rcu_head **nxttail;
struct rcu_head *curlist;
};
DECLARE_PER_CPU(struct rcu_data, rcu_data);
extern struct rcu_ctrlblk rcu_ctrlblk;
#define RCU_quiescbatch(cpu) (per_cpu(rcu_data, (cpu)).quiescbatch)
#define RCU_qsctr(cpu) (per_cpu(rcu_data, (cpu)).qsctr)
#define RCU_last_qsctr(cpu) (per_cpu(rcu_data, (cpu)).last_qsctr)
#define RCU_qs_pending(cpu) (per_cpu(rcu_data, (cpu)).qs_pending)
#define RCU_batch(cpu) (per_cpu(rcu_data, (cpu)).batch)
#define RCU_nxtlist(cpu) (per_cpu(rcu_data, (cpu)).nxtlist)
#define RCU_curlist(cpu) (per_cpu(rcu_data, (cpu)).curlist)
#define RCU_nxttail(cpu) (per_cpu(rcu_data, (cpu)).nxttail)
static inline int rcu_pending(int cpu)
{
/* This cpu has pending rcu entries and the grace period
* for them has completed.
*/
if (RCU_curlist(cpu) &&
!rcu_batch_before(rcu_ctrlblk.completed,RCU_batch(cpu)))
return 1;
/* This cpu has no pending entries, but there are new entries */
if (!RCU_curlist(cpu) && RCU_nxtlist(cpu))
return 1;
/* The rcu core waits for a quiescent state from the cpu */
if (RCU_quiescbatch(cpu) != rcu_ctrlblk.cur || RCU_qs_pending(cpu))
return 1;
/* nothing to do */
return 0;
}
#define rcu_read_lock() preempt_disable()
#define rcu_read_unlock() preempt_enable()
extern void rcu_init(void);
extern void rcu_check_callbacks(int cpu, int user);
extern void rcu_restart_cpu(int cpu);
/* Exported interfaces */
extern void FASTCALL(call_rcu(struct rcu_head *head,
void (*func)(struct rcu_head *head)));
extern void synchronize_kernel(void);
#endif /* __KERNEL__ */
#endif /* __LINUX_RCUPDATE_H */
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