293 lines
9.7 KiB
C
293 lines
9.7 KiB
C
/*
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* Read-Copy Update mechanism for mutual exclusion
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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*
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* Copyright (C) IBM Corporation, 2001
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*
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* Author: Dipankar Sarma <dipankar@in.ibm.com>
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*
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* Based on the original work by Paul McKenney <paul.mckenney@us.ibm.com>
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* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
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* Papers:
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* http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
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* http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
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*
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* For detailed explanation of Read-Copy Update mechanism see -
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* http://lse.sourceforge.net/locking/rcupdate.html
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*
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*/
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#ifndef __LINUX_RCUPDATE_H
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#define __LINUX_RCUPDATE_H
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#ifdef __KERNEL__
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#include <linux/cache.h>
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#include <linux/spinlock.h>
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#include <linux/threads.h>
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#include <linux/percpu.h>
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#include <linux/cpumask.h>
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#include <linux/seqlock.h>
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/**
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* struct rcu_head - callback structure for use with RCU
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* @next: next update requests in a list
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* @func: actual update function to call after the grace period.
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*/
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struct rcu_head {
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struct rcu_head *next;
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void (*func)(struct rcu_head *head);
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};
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#define RCU_HEAD_INIT { .next = NULL, .func = NULL }
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#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
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#define INIT_RCU_HEAD(ptr) do { \
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(ptr)->next = NULL; (ptr)->func = NULL; \
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} while (0)
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/* Global control variables for rcupdate callback mechanism. */
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struct rcu_ctrlblk {
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long cur; /* Current batch number. */
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long completed; /* Number of the last completed batch */
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int next_pending; /* Is the next batch already waiting? */
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} ____cacheline_maxaligned_in_smp;
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/* Is batch a before batch b ? */
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static inline int rcu_batch_before(long a, long b)
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{
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return (a - b) < 0;
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}
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/* Is batch a after batch b ? */
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static inline int rcu_batch_after(long a, long b)
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{
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return (a - b) > 0;
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}
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/*
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* Per-CPU data for Read-Copy UPdate.
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* nxtlist - new callbacks are added here
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* curlist - current batch for which quiescent cycle started if any
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*/
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struct rcu_data {
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/* 1) quiescent state handling : */
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long quiescbatch; /* Batch # for grace period */
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int passed_quiesc; /* User-mode/idle loop etc. */
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int qs_pending; /* core waits for quiesc state */
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/* 2) batch handling */
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long batch; /* Batch # for current RCU batch */
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struct rcu_head *nxtlist;
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struct rcu_head **nxttail;
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long count; /* # of queued items */
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struct rcu_head *curlist;
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struct rcu_head **curtail;
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struct rcu_head *donelist;
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struct rcu_head **donetail;
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int cpu;
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struct rcu_head barrier;
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};
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DECLARE_PER_CPU(struct rcu_data, rcu_data);
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DECLARE_PER_CPU(struct rcu_data, rcu_bh_data);
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extern struct rcu_ctrlblk rcu_ctrlblk;
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extern struct rcu_ctrlblk rcu_bh_ctrlblk;
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/*
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* Increment the quiescent state counter.
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* The counter is a bit degenerated: We do not need to know
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* how many quiescent states passed, just if there was at least
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* one since the start of the grace period. Thus just a flag.
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*/
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static inline void rcu_qsctr_inc(int cpu)
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{
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struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
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rdp->passed_quiesc = 1;
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}
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static inline void rcu_bh_qsctr_inc(int cpu)
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{
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struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
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rdp->passed_quiesc = 1;
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}
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static inline int __rcu_pending(struct rcu_ctrlblk *rcp,
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struct rcu_data *rdp)
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{
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/* This cpu has pending rcu entries and the grace period
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* for them has completed.
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*/
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if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch))
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return 1;
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/* This cpu has no pending entries, but there are new entries */
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if (!rdp->curlist && rdp->nxtlist)
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return 1;
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/* This cpu has finished callbacks to invoke */
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if (rdp->donelist)
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return 1;
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/* The rcu core waits for a quiescent state from the cpu */
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if (rdp->quiescbatch != rcp->cur || rdp->qs_pending)
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return 1;
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/* nothing to do */
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return 0;
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}
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static inline int rcu_pending(int cpu)
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{
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return __rcu_pending(&rcu_ctrlblk, &per_cpu(rcu_data, cpu)) ||
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__rcu_pending(&rcu_bh_ctrlblk, &per_cpu(rcu_bh_data, cpu));
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}
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/**
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* rcu_read_lock - mark the beginning of an RCU read-side critical section.
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*
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* When synchronize_rcu() is invoked on one CPU while other CPUs
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* are within RCU read-side critical sections, then the
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* synchronize_rcu() is guaranteed to block until after all the other
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* CPUs exit their critical sections. Similarly, if call_rcu() is invoked
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* on one CPU while other CPUs are within RCU read-side critical
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* sections, invocation of the corresponding RCU callback is deferred
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* until after the all the other CPUs exit their critical sections.
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*
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* Note, however, that RCU callbacks are permitted to run concurrently
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* with RCU read-side critical sections. One way that this can happen
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* is via the following sequence of events: (1) CPU 0 enters an RCU
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* read-side critical section, (2) CPU 1 invokes call_rcu() to register
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* an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
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* (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
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* callback is invoked. This is legal, because the RCU read-side critical
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* section that was running concurrently with the call_rcu() (and which
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* therefore might be referencing something that the corresponding RCU
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* callback would free up) has completed before the corresponding
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* RCU callback is invoked.
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*
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* RCU read-side critical sections may be nested. Any deferred actions
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* will be deferred until the outermost RCU read-side critical section
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* completes.
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*
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* It is illegal to block while in an RCU read-side critical section.
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*/
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#define rcu_read_lock() preempt_disable()
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/**
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* rcu_read_unlock - marks the end of an RCU read-side critical section.
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*
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* See rcu_read_lock() for more information.
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*/
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#define rcu_read_unlock() preempt_enable()
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/*
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* So where is rcu_write_lock()? It does not exist, as there is no
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* way for writers to lock out RCU readers. This is a feature, not
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* a bug -- this property is what provides RCU's performance benefits.
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* Of course, writers must coordinate with each other. The normal
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* spinlock primitives work well for this, but any other technique may be
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* used as well. RCU does not care how the writers keep out of each
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* others' way, as long as they do so.
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*/
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/**
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* rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
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*
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* This is equivalent of rcu_read_lock(), but to be used when updates
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* are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
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* consider completion of a softirq handler to be a quiescent state,
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* a process in RCU read-side critical section must be protected by
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* disabling softirqs. Read-side critical sections in interrupt context
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* can use just rcu_read_lock().
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*
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*/
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#define rcu_read_lock_bh() local_bh_disable()
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/*
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* rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
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*
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* See rcu_read_lock_bh() for more information.
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*/
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#define rcu_read_unlock_bh() local_bh_enable()
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/**
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* rcu_dereference - fetch an RCU-protected pointer in an
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* RCU read-side critical section. This pointer may later
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* be safely dereferenced.
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*
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* Inserts memory barriers on architectures that require them
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* (currently only the Alpha), and, more importantly, documents
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* exactly which pointers are protected by RCU.
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*/
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#define rcu_dereference(p) ({ \
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typeof(p) _________p1 = p; \
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smp_read_barrier_depends(); \
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(_________p1); \
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})
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/**
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* rcu_assign_pointer - assign (publicize) a pointer to a newly
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* initialized structure that will be dereferenced by RCU read-side
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* critical sections. Returns the value assigned.
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*
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* Inserts memory barriers on architectures that require them
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* (pretty much all of them other than x86), and also prevents
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* the compiler from reordering the code that initializes the
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* structure after the pointer assignment. More importantly, this
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* call documents which pointers will be dereferenced by RCU read-side
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* code.
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*/
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#define rcu_assign_pointer(p, v) ({ \
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smp_wmb(); \
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(p) = (v); \
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})
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/**
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* synchronize_sched - block until all CPUs have exited any non-preemptive
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* kernel code sequences.
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*
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* This means that all preempt_disable code sequences, including NMI and
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* hardware-interrupt handlers, in progress on entry will have completed
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* before this primitive returns. However, this does not guarantee that
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* softirq handlers will have completed, since in some kernels
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*
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* This primitive provides the guarantees made by the (deprecated)
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* synchronize_kernel() API. In contrast, synchronize_rcu() only
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* guarantees that rcu_read_lock() sections will have completed.
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*/
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#define synchronize_sched() synchronize_rcu()
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extern void rcu_init(void);
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extern void rcu_check_callbacks(int cpu, int user);
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extern void rcu_restart_cpu(int cpu);
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extern long rcu_batches_completed(void);
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/* Exported interfaces */
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extern void FASTCALL(call_rcu(struct rcu_head *head,
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void (*func)(struct rcu_head *head)));
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extern void FASTCALL(call_rcu_bh(struct rcu_head *head,
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void (*func)(struct rcu_head *head)));
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extern __deprecated_for_modules void synchronize_kernel(void);
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extern void synchronize_rcu(void);
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void synchronize_idle(void);
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extern void rcu_barrier(void);
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#endif /* __KERNEL__ */
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#endif /* __LINUX_RCUPDATE_H */
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