/*
* Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
*
* 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 IBM Corporation, 2008
*
* Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
*
* For detailed explanation of Read-Copy Update mechanism see -
* Documentation/RCU
*/
#include <linux/moduleparam.h>
#include <linux/completion.h>
#include <linux/interrupt.h>
#include <linux/notifier.h>
#include <linux/rcupdate.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/sched.h>
#include <linux/types.h>
#include <linux/init.h>
#include <linux/time.h>
#include <linux/cpu.h>
/* Global control variables for rcupdate callback mechanism. */
struct rcu_ctrlblk {
struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */
struct rcu_head **donetail; /* ->next pointer of last "done" CB. */
struct rcu_head **curtail; /* ->next pointer of last CB. */
};
/* Definition for rcupdate control block. */
static struct rcu_ctrlblk rcu_ctrlblk = {
.donetail = &rcu_ctrlblk.rcucblist,
.curtail = &rcu_ctrlblk.rcucblist,
};
static struct rcu_ctrlblk rcu_bh_ctrlblk = {
.donetail = &rcu_bh_ctrlblk.rcucblist,
.curtail = &rcu_bh_ctrlblk.rcucblist,
};
#ifdef CONFIG_NO_HZ
static long rcu_dynticks_nesting = 1;
/*
* Enter dynticks-idle mode, which is an extended quiescent state
* if we have fully entered that mode (i.e., if the new value of
* dynticks_nesting is zero).
*/
void rcu_enter_nohz(void)
{
if (--rcu_dynticks_nesting == 0)
rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
}
/*
* Exit dynticks-idle mode, so that we are no longer in an extended
* quiescent state.
*/
void rcu_exit_nohz(void)
{
rcu_dynticks_nesting++;
}
#endif /* #ifdef CONFIG_NO_HZ */
/*
* Helper function for rcu_qsctr_inc() and rcu_bh_qsctr_inc().
* Also disable irqs to avoid confusion due to interrupt handlers
* invoking call_rcu().
*/
static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
{
unsigned long flags;
local_irq_save(flags);
if (rcp->rcucblist != NULL &&
rcp->donetail != rcp->curtail) {
rcp->donetail = rcp->curtail;
local_irq_restore(flags);
return 1;
}
local_irq_restore(flags);
return 0;
}
/*
* Record an rcu quiescent state. And an rcu_bh quiescent state while we
* are at it, given that any rcu quiescent state is also an rcu_bh
* quiescent state. Use "+" instead of "||" to defeat short circuiting.
*/
void rcu_sched_qs(int cpu)
{
if (rcu_qsctr_help(&rcu_ctrlblk) + rcu_qsctr_help(&rcu_bh_ctrlblk))
raise_softirq(RCU_SOFTIRQ);
}
/*
* Record an rcu_bh quiescent state.
*/
void rcu_bh_qs(int cpu)
{
if (rcu_qsctr_help(&rcu_bh_ctrlblk))
raise_softirq(RCU_SOFTIRQ);
}
/*
* Check to see if the scheduling-clock interrupt came from an extended
* quiescent state, and, if so, tell RCU about it.
*/
void rcu_check_callbacks(int cpu, int user)
{
if (user ||
(idle_cpu(cpu) &&
!in_softirq() &&
hardirq_count() <= (1 << HARDIRQ_SHIFT)))
rcu_sched_qs(cpu);
else if (!in_softirq())
rcu_bh_qs(cpu);
}
/*
* Helper function for rcu_process_callbacks() that operates on the
* specified rcu_ctrlkblk structure.
*/
static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
{
struct rcu_head *next, *list;
unsigned long flags;
/* If no RCU callbacks ready to invoke, just return. */
if (&rcp->rcucblist == rcp->donetail)
return;
/* Move the ready-to-invoke callbacks to a local list. */
local_irq_save(flags);
list = rcp->rcucblist;
rcp->rcucblist = *rcp->donetail;
*rcp->donetail = NULL;
if (rcp->curtail == rcp->donetail)
rcp->curtail = &rcp->rcucblist;
rcp->donetail = &rcp->rcucblist;
local_irq_restore(flags);
/* Invoke the callbacks on the local list. */
while (list) {
next = list->next;
prefetch(next);
list->func(list);
list = next;
}
}
/*
* Invoke any callbacks whose grace period has completed.
*/
static void rcu_process_callbacks(struct softirq_action *unused)
{
__rcu_process_callbacks(&rcu_ctrlblk);
__rcu_process_callbacks(&rcu_bh_ctrlblk);
}
/*
* Wait for a grace period to elapse. But it is illegal to invoke
* synchronize_sched() from within an RCU read-side critical section.
* Therefore, any legal call to synchronize_sched() is a quiescent
* state, and so on a UP system, synchronize_sched() need do nothing.
* Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the
* benefits of doing might_sleep() to reduce latency.)
*
* Cool, huh? (Due to Josh Triplett.)
*
* But we want to make this a static inline later.
*/
void synchronize_sched(void)
{
cond_resched();
}
EXPORT_SYMBOL_GPL(synchronize_sched);
void synchronize_rcu_bh(void)
{
synchronize_sched();
}
EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
/*
* Helper function for call_rcu() and call_rcu_bh().
*/
static void __call_rcu(struct rcu_head *head,
void (*func)(struct rcu_head *rcu),
struct rcu_ctrlblk *rcp)
{
unsigned long flags;
head->func = func;
head->next = NULL;
local_irq_save(flags);
*rcp->curtail = head;
rcp->curtail = &head->next;
local_irq_restore(flags);
}
/*
* Post an RCU callback to be invoked after the end of an RCU grace
* period. But since we have but one CPU, that would be after any
* quiescent state.
*/
void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
__call_rcu(head, func, &rcu_ctrlblk);
}
EXPORT_SYMBOL_GPL(call_rcu);
/*
* Post an RCU bottom-half callback to be invoked after any subsequent
* quiescent state.
*/
void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
__call_rcu(head, func, &rcu_bh_ctrlblk);
}
EXPORT_SYMBOL_GPL(call_rcu_bh);
void rcu_barrier(void)
{
struct rcu_synchronize rcu;
init_completion(&rcu.completion);
/* Will wake me after RCU finished. */
call_rcu(&rcu.head, wakeme_after_rcu);
/* Wait for it. */
wait_for_completion(&rcu.completion);
}
EXPORT_SYMBOL_GPL(rcu_barrier);
void rcu_barrier_bh(void)
{
struct rcu_synchronize rcu;
init_completion(&rcu.completion);
/* Will wake me after RCU finished. */
call_rcu_bh(&rcu.head, wakeme_after_rcu);
/* Wait for it. */
wait_for_completion(&rcu.completion);
}
EXPORT_SYMBOL_GPL(rcu_barrier_bh);
void rcu_barrier_sched(void)
{
struct rcu_synchronize rcu;
init_completion(&rcu.completion);
/* Will wake me after RCU finished. */
call_rcu_sched(&rcu.head, wakeme_after_rcu);
/* Wait for it. */
wait_for_completion(&rcu.completion);
}
EXPORT_SYMBOL_GPL(rcu_barrier_sched);
void __init rcu_init(void)
{
open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
}
