2008-01-25 21:08:24 +01:00
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/*
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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 IBM Corporation, 2001
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*
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* Authors: Dipankar Sarma <dipankar@in.ibm.com>
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* Manfred Spraul <manfred@colorfullife.com>
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*
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* Based on the original work by Paul McKenney <paulmck@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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* Documentation/RCU
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*
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*/
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#include <linux/types.h>
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#include <linux/kernel.h>
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#include <linux/init.h>
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#include <linux/spinlock.h>
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#include <linux/smp.h>
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#include <linux/rcupdate.h>
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#include <linux/interrupt.h>
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#include <linux/sched.h>
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#include <asm/atomic.h>
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#include <linux/bitops.h>
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#include <linux/module.h>
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#include <linux/completion.h>
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#include <linux/moduleparam.h>
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#include <linux/percpu.h>
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#include <linux/notifier.h>
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#include <linux/cpu.h>
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#include <linux/mutex.h>
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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static struct lock_class_key rcu_lock_key;
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struct lockdep_map rcu_lock_map =
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STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
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EXPORT_SYMBOL_GPL(rcu_lock_map);
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#endif
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/* Definition for rcupdate control block. */
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static struct rcu_ctrlblk rcu_ctrlblk = {
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.cur = -300,
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.completed = -300,
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.lock = __SPIN_LOCK_UNLOCKED(&rcu_ctrlblk.lock),
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.cpumask = CPU_MASK_NONE,
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};
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static struct rcu_ctrlblk rcu_bh_ctrlblk = {
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.cur = -300,
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.completed = -300,
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.lock = __SPIN_LOCK_UNLOCKED(&rcu_bh_ctrlblk.lock),
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.cpumask = CPU_MASK_NONE,
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};
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DEFINE_PER_CPU(struct rcu_data, rcu_data) = { 0L };
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DEFINE_PER_CPU(struct rcu_data, rcu_bh_data) = { 0L };
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static int blimit = 10;
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static int qhimark = 10000;
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static int qlowmark = 100;
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#ifdef CONFIG_SMP
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static void force_quiescent_state(struct rcu_data *rdp,
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struct rcu_ctrlblk *rcp)
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{
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int cpu;
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cpumask_t cpumask;
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set_need_resched();
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if (unlikely(!rcp->signaled)) {
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rcp->signaled = 1;
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/*
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* Don't send IPI to itself. With irqs disabled,
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* rdp->cpu is the current cpu.
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rcu: fix hotplug vs rcu race
Dhaval Giani reported this warning during cpu hotplug stress-tests:
| On running kernel compiles in parallel with cpu hotplug:
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| WARNING: at arch/x86/kernel/smp.c:118
| native_smp_send_reschedule+0x21/0x36()
| Modules linked in:
| Pid: 27483, comm: cc1 Not tainted 2.6.26-rc7 #1
| [...]
| [<c0110355>] native_smp_send_reschedule+0x21/0x36
| [<c014fe8f>] force_quiescent_state+0x47/0x57
| [<c014fef0>] call_rcu+0x51/0x6d
| [<c01713b3>] __fput+0x130/0x158
| [<c0171231>] fput+0x17/0x19
| [<c016fd99>] filp_close+0x4d/0x57
| [<c016fdff>] sys_close+0x5c/0x97
IMHO the warning is a spurious one.
cpu_online_map is updated by the _cpu_down() using stop_machine_run().
Since force_quiescent_state is invoked from irqs disabled section,
stop_machine_run() won't be executing while a cpu is executing
force_quiescent_state(). Hence the cpu_online_map is stable while we're
in the irq disabled section.
However, a cpu might have been offlined _just_ before we disabled irqs
while entering force_quiescent_state(). And rcu subsystem might not yet
have handled the CPU_DEAD notification, leading to the offlined cpu's
bit being set in the rcp->cpumask.
Hence cpumask = (rcp->cpumask & cpu_online_map) to prevent sending
smp_reschedule() to an offlined CPU.
Here's the timeline:
CPU_A CPU_B
--------------------------------------------------------------
cpu_down(): .
. .
. .
stop_machine(): /* disables preemption, .
* and irqs */ .
. .
. .
take_cpu_down(); .
. .
. .
. .
cpu_disable(); /*this removes cpu .
*from cpu_online_map .
*/ .
. .
. .
restart_machine(); /* enables irqs */ .
------WINDOW DURING WHICH rcp->cpumask is stale ---------------
. call_rcu();
. /* disables irqs here */
. .force_quiescent_state();
.CPU_DEAD: .for_each_cpu(rcp->cpumask)
. . smp_send_reschedule();
. .
. . WARN_ON() for offlined CPU!
.
.
.
rcu_cpu_notify:
.
-------- WINDOW ENDS ------------------------------------------
rcu_offline_cpu() /* Which calls cpu_quiet()
* which removes
* cpu from rcp->cpumask.
*/
If a new batch was started just before calling stop_machine_run(), the
"tobe-offlined" cpu is still present in rcp-cpumask.
During a cpu-offline, from take_cpu_down(), we queue an rt-prio idle
task as the next task to be picked by the scheduler. We also call
cpu_disable() which will disable any further interrupts and remove the
cpu's bit from the cpu_online_map.
Once the stop_machine_run() successfully calls take_cpu_down(), it calls
schedule(). That's the last time a schedule is called on the offlined
cpu, and hence the last time when rdp->passed_quiesc will be set to 1
through rcu_qsctr_inc().
But the cpu_quiet() will be on this cpu will be called only when the
next RCU_SOFTIRQ occurs on this CPU. So at this time, the offlined CPU
is still set in rcp->cpumask.
Now coming back to the idle_task which truely offlines the CPU, it does
check for a pending RCU and raises the softirq, since it will find
rdp->passed_quiesc to be 0 in this case. However, since the cpu is
offline I am not sure if the softirq will trigger on the CPU.
Even if it doesn't the rcu_offline_cpu() will find that rcp->completed
is not the same as rcp->cur, which means that our cpu could be holding
up the grace period progression. Hence we call cpu_quiet() and move
ahead.
But because of the window explained in the timeline, we could still have
a call_rcu() before the RCU subsystem executes it's CPU_DEAD
notification, and we send smp_send_reschedule() to offlined cpu while
trying to force the quiescent states. The appended patch adds comments
and prevents checking for offlined cpu everytime.
cpu_online_map is updated by the _cpu_down() using stop_machine_run().
Since force_quiescent_state is invoked from irqs disabled section,
stop_machine_run() won't be executing while a cpu is executing
force_quiescent_state(). Hence the cpu_online_map is stable while we're
in the irq disabled section.
Reported-by: Dhaval Giani <dhaval@linux.vnet.ibm.com>
Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Acked-by: Dhaval Giani <dhaval@linux.vnet.ibm.com>
Cc: Dipankar Sarma <dipankar@in.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Rusty Russel <rusty@rustcorp.com.au>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-06-27 06:47:38 +02:00
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*
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* cpu_online_map is updated by the _cpu_down()
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* using stop_machine_run(). Since we're in irqs disabled
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* section, stop_machine_run() is not exectuting, hence
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* the cpu_online_map is stable.
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*
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* However, a cpu might have been offlined _just_ before
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* we disabled irqs while entering here.
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* And rcu subsystem might not yet have handled the CPU_DEAD
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* notification, leading to the offlined cpu's bit
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* being set in the rcp->cpumask.
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*
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* Hence cpumask = (rcp->cpumask & cpu_online_map) to prevent
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* sending smp_reschedule() to an offlined CPU.
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2008-01-25 21:08:24 +01:00
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*/
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rcu: fix hotplug vs rcu race
Dhaval Giani reported this warning during cpu hotplug stress-tests:
| On running kernel compiles in parallel with cpu hotplug:
|
| WARNING: at arch/x86/kernel/smp.c:118
| native_smp_send_reschedule+0x21/0x36()
| Modules linked in:
| Pid: 27483, comm: cc1 Not tainted 2.6.26-rc7 #1
| [...]
| [<c0110355>] native_smp_send_reschedule+0x21/0x36
| [<c014fe8f>] force_quiescent_state+0x47/0x57
| [<c014fef0>] call_rcu+0x51/0x6d
| [<c01713b3>] __fput+0x130/0x158
| [<c0171231>] fput+0x17/0x19
| [<c016fd99>] filp_close+0x4d/0x57
| [<c016fdff>] sys_close+0x5c/0x97
IMHO the warning is a spurious one.
cpu_online_map is updated by the _cpu_down() using stop_machine_run().
Since force_quiescent_state is invoked from irqs disabled section,
stop_machine_run() won't be executing while a cpu is executing
force_quiescent_state(). Hence the cpu_online_map is stable while we're
in the irq disabled section.
However, a cpu might have been offlined _just_ before we disabled irqs
while entering force_quiescent_state(). And rcu subsystem might not yet
have handled the CPU_DEAD notification, leading to the offlined cpu's
bit being set in the rcp->cpumask.
Hence cpumask = (rcp->cpumask & cpu_online_map) to prevent sending
smp_reschedule() to an offlined CPU.
Here's the timeline:
CPU_A CPU_B
--------------------------------------------------------------
cpu_down(): .
. .
. .
stop_machine(): /* disables preemption, .
* and irqs */ .
. .
. .
take_cpu_down(); .
. .
. .
. .
cpu_disable(); /*this removes cpu .
*from cpu_online_map .
*/ .
. .
. .
restart_machine(); /* enables irqs */ .
------WINDOW DURING WHICH rcp->cpumask is stale ---------------
. call_rcu();
. /* disables irqs here */
. .force_quiescent_state();
.CPU_DEAD: .for_each_cpu(rcp->cpumask)
. . smp_send_reschedule();
. .
. . WARN_ON() for offlined CPU!
.
.
.
rcu_cpu_notify:
.
-------- WINDOW ENDS ------------------------------------------
rcu_offline_cpu() /* Which calls cpu_quiet()
* which removes
* cpu from rcp->cpumask.
*/
If a new batch was started just before calling stop_machine_run(), the
"tobe-offlined" cpu is still present in rcp-cpumask.
During a cpu-offline, from take_cpu_down(), we queue an rt-prio idle
task as the next task to be picked by the scheduler. We also call
cpu_disable() which will disable any further interrupts and remove the
cpu's bit from the cpu_online_map.
Once the stop_machine_run() successfully calls take_cpu_down(), it calls
schedule(). That's the last time a schedule is called on the offlined
cpu, and hence the last time when rdp->passed_quiesc will be set to 1
through rcu_qsctr_inc().
But the cpu_quiet() will be on this cpu will be called only when the
next RCU_SOFTIRQ occurs on this CPU. So at this time, the offlined CPU
is still set in rcp->cpumask.
Now coming back to the idle_task which truely offlines the CPU, it does
check for a pending RCU and raises the softirq, since it will find
rdp->passed_quiesc to be 0 in this case. However, since the cpu is
offline I am not sure if the softirq will trigger on the CPU.
Even if it doesn't the rcu_offline_cpu() will find that rcp->completed
is not the same as rcp->cur, which means that our cpu could be holding
up the grace period progression. Hence we call cpu_quiet() and move
ahead.
But because of the window explained in the timeline, we could still have
a call_rcu() before the RCU subsystem executes it's CPU_DEAD
notification, and we send smp_send_reschedule() to offlined cpu while
trying to force the quiescent states. The appended patch adds comments
and prevents checking for offlined cpu everytime.
cpu_online_map is updated by the _cpu_down() using stop_machine_run().
Since force_quiescent_state is invoked from irqs disabled section,
stop_machine_run() won't be executing while a cpu is executing
force_quiescent_state(). Hence the cpu_online_map is stable while we're
in the irq disabled section.
Reported-by: Dhaval Giani <dhaval@linux.vnet.ibm.com>
Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Acked-by: Dhaval Giani <dhaval@linux.vnet.ibm.com>
Cc: Dipankar Sarma <dipankar@in.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Rusty Russel <rusty@rustcorp.com.au>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-06-27 06:47:38 +02:00
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cpus_and(cpumask, rcp->cpumask, cpu_online_map);
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2008-01-25 21:08:24 +01:00
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cpu_clear(rdp->cpu, cpumask);
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for_each_cpu_mask(cpu, cpumask)
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smp_send_reschedule(cpu);
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}
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}
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#else
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static inline void force_quiescent_state(struct rcu_data *rdp,
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struct rcu_ctrlblk *rcp)
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{
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set_need_resched();
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}
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#endif
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/**
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* call_rcu - Queue an RCU callback for invocation after a grace period.
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* @head: structure to be used for queueing the RCU updates.
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* @func: actual update function to be invoked after the grace period
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*
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* The update function will be invoked some time after a full grace
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* period elapses, in other words after all currently executing RCU
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* read-side critical sections have completed. RCU read-side critical
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* sections are delimited by rcu_read_lock() and rcu_read_unlock(),
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* and may be nested.
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*/
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void call_rcu(struct rcu_head *head,
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void (*func)(struct rcu_head *rcu))
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{
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unsigned long flags;
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struct rcu_data *rdp;
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head->func = func;
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head->next = NULL;
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local_irq_save(flags);
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rdp = &__get_cpu_var(rcu_data);
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*rdp->nxttail = head;
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rdp->nxttail = &head->next;
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if (unlikely(++rdp->qlen > qhimark)) {
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rdp->blimit = INT_MAX;
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force_quiescent_state(rdp, &rcu_ctrlblk);
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}
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local_irq_restore(flags);
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}
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EXPORT_SYMBOL_GPL(call_rcu);
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/**
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* call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
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* @head: structure to be used for queueing the RCU updates.
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* @func: actual update function to be invoked after the grace period
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*
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* The update function will be invoked some time after a full grace
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* period elapses, in other words after all currently executing RCU
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* read-side critical sections have completed. call_rcu_bh() assumes
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* that the read-side critical sections end on completion of a softirq
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* handler. This means that read-side critical sections in process
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* context must not be interrupted by softirqs. This interface is to be
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* used when most of the read-side critical sections are in softirq context.
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* RCU read-side critical sections are delimited by rcu_read_lock() and
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* rcu_read_unlock(), * if in interrupt context or rcu_read_lock_bh()
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* and rcu_read_unlock_bh(), if in process context. These may be nested.
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*/
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void call_rcu_bh(struct rcu_head *head,
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void (*func)(struct rcu_head *rcu))
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{
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unsigned long flags;
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struct rcu_data *rdp;
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head->func = func;
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head->next = NULL;
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local_irq_save(flags);
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rdp = &__get_cpu_var(rcu_bh_data);
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*rdp->nxttail = head;
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rdp->nxttail = &head->next;
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if (unlikely(++rdp->qlen > qhimark)) {
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rdp->blimit = INT_MAX;
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force_quiescent_state(rdp, &rcu_bh_ctrlblk);
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}
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local_irq_restore(flags);
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}
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EXPORT_SYMBOL_GPL(call_rcu_bh);
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/*
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* Return the number of RCU batches processed thus far. Useful
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* for debug and statistics.
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*/
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long rcu_batches_completed(void)
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{
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return rcu_ctrlblk.completed;
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}
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EXPORT_SYMBOL_GPL(rcu_batches_completed);
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/*
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* Return the number of RCU batches processed thus far. Useful
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* for debug and statistics.
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*/
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long rcu_batches_completed_bh(void)
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{
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return rcu_bh_ctrlblk.completed;
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}
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EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
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/* Raises the softirq for processing rcu_callbacks. */
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static inline void raise_rcu_softirq(void)
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{
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raise_softirq(RCU_SOFTIRQ);
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/*
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* The smp_mb() here is required to ensure that this cpu's
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|
|
* __rcu_process_callbacks() reads the most recently updated
|
|
|
|
* value of rcu->cur.
|
|
|
|
*/
|
|
|
|
smp_mb();
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* Invoke the completed RCU callbacks. They are expected to be in
|
|
|
|
* a per-cpu list.
|
|
|
|
*/
|
|
|
|
static void rcu_do_batch(struct rcu_data *rdp)
|
|
|
|
{
|
|
|
|
struct rcu_head *next, *list;
|
|
|
|
int count = 0;
|
|
|
|
|
|
|
|
list = rdp->donelist;
|
|
|
|
while (list) {
|
|
|
|
next = list->next;
|
|
|
|
prefetch(next);
|
|
|
|
list->func(list);
|
|
|
|
list = next;
|
|
|
|
if (++count >= rdp->blimit)
|
|
|
|
break;
|
|
|
|
}
|
|
|
|
rdp->donelist = list;
|
|
|
|
|
|
|
|
local_irq_disable();
|
|
|
|
rdp->qlen -= count;
|
|
|
|
local_irq_enable();
|
|
|
|
if (rdp->blimit == INT_MAX && rdp->qlen <= qlowmark)
|
|
|
|
rdp->blimit = blimit;
|
|
|
|
|
|
|
|
if (!rdp->donelist)
|
|
|
|
rdp->donetail = &rdp->donelist;
|
|
|
|
else
|
|
|
|
raise_rcu_softirq();
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* Grace period handling:
|
|
|
|
* The grace period handling consists out of two steps:
|
|
|
|
* - A new grace period is started.
|
|
|
|
* This is done by rcu_start_batch. The start is not broadcasted to
|
|
|
|
* all cpus, they must pick this up by comparing rcp->cur with
|
|
|
|
* rdp->quiescbatch. All cpus are recorded in the
|
|
|
|
* rcu_ctrlblk.cpumask bitmap.
|
|
|
|
* - All cpus must go through a quiescent state.
|
|
|
|
* Since the start of the grace period is not broadcasted, at least two
|
|
|
|
* calls to rcu_check_quiescent_state are required:
|
|
|
|
* The first call just notices that a new grace period is running. The
|
|
|
|
* following calls check if there was a quiescent state since the beginning
|
|
|
|
* of the grace period. If so, it updates rcu_ctrlblk.cpumask. If
|
|
|
|
* the bitmap is empty, then the grace period is completed.
|
|
|
|
* rcu_check_quiescent_state calls rcu_start_batch(0) to start the next grace
|
|
|
|
* period (if necessary).
|
|
|
|
*/
|
|
|
|
/*
|
|
|
|
* Register a new batch of callbacks, and start it up if there is currently no
|
|
|
|
* active batch and the batch to be registered has not already occurred.
|
|
|
|
* Caller must hold rcu_ctrlblk.lock.
|
|
|
|
*/
|
|
|
|
static void rcu_start_batch(struct rcu_ctrlblk *rcp)
|
|
|
|
{
|
|
|
|
if (rcp->next_pending &&
|
|
|
|
rcp->completed == rcp->cur) {
|
|
|
|
rcp->next_pending = 0;
|
|
|
|
/*
|
|
|
|
* next_pending == 0 must be visible in
|
|
|
|
* __rcu_process_callbacks() before it can see new value of cur.
|
|
|
|
*/
|
|
|
|
smp_wmb();
|
|
|
|
rcp->cur++;
|
|
|
|
|
|
|
|
/*
|
|
|
|
* Accessing nohz_cpu_mask before incrementing rcp->cur needs a
|
|
|
|
* Barrier Otherwise it can cause tickless idle CPUs to be
|
|
|
|
* included in rcp->cpumask, which will extend graceperiods
|
|
|
|
* unnecessarily.
|
|
|
|
*/
|
|
|
|
smp_mb();
|
|
|
|
cpus_andnot(rcp->cpumask, cpu_online_map, nohz_cpu_mask);
|
|
|
|
|
|
|
|
rcp->signaled = 0;
|
|
|
|
}
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* cpu went through a quiescent state since the beginning of the grace period.
|
|
|
|
* Clear it from the cpu mask and complete the grace period if it was the last
|
|
|
|
* cpu. Start another grace period if someone has further entries pending
|
|
|
|
*/
|
|
|
|
static void cpu_quiet(int cpu, struct rcu_ctrlblk *rcp)
|
|
|
|
{
|
|
|
|
cpu_clear(cpu, rcp->cpumask);
|
|
|
|
if (cpus_empty(rcp->cpumask)) {
|
|
|
|
/* batch completed ! */
|
|
|
|
rcp->completed = rcp->cur;
|
|
|
|
rcu_start_batch(rcp);
|
|
|
|
}
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* Check if the cpu has gone through a quiescent state (say context
|
|
|
|
* switch). If so and if it already hasn't done so in this RCU
|
|
|
|
* quiescent cycle, then indicate that it has done so.
|
|
|
|
*/
|
|
|
|
static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp,
|
|
|
|
struct rcu_data *rdp)
|
|
|
|
{
|
|
|
|
if (rdp->quiescbatch != rcp->cur) {
|
|
|
|
/* start new grace period: */
|
|
|
|
rdp->qs_pending = 1;
|
|
|
|
rdp->passed_quiesc = 0;
|
|
|
|
rdp->quiescbatch = rcp->cur;
|
|
|
|
return;
|
|
|
|
}
|
|
|
|
|
|
|
|
/* Grace period already completed for this cpu?
|
|
|
|
* qs_pending is checked instead of the actual bitmap to avoid
|
|
|
|
* cacheline trashing.
|
|
|
|
*/
|
|
|
|
if (!rdp->qs_pending)
|
|
|
|
return;
|
|
|
|
|
|
|
|
/*
|
|
|
|
* Was there a quiescent state since the beginning of the grace
|
|
|
|
* period? If no, then exit and wait for the next call.
|
|
|
|
*/
|
|
|
|
if (!rdp->passed_quiesc)
|
|
|
|
return;
|
|
|
|
rdp->qs_pending = 0;
|
|
|
|
|
|
|
|
spin_lock(&rcp->lock);
|
|
|
|
/*
|
|
|
|
* rdp->quiescbatch/rcp->cur and the cpu bitmap can come out of sync
|
|
|
|
* during cpu startup. Ignore the quiescent state.
|
|
|
|
*/
|
|
|
|
if (likely(rdp->quiescbatch == rcp->cur))
|
|
|
|
cpu_quiet(rdp->cpu, rcp);
|
|
|
|
|
|
|
|
spin_unlock(&rcp->lock);
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
|
|
#ifdef CONFIG_HOTPLUG_CPU
|
|
|
|
|
|
|
|
/* warning! helper for rcu_offline_cpu. do not use elsewhere without reviewing
|
|
|
|
* locking requirements, the list it's pulling from has to belong to a cpu
|
|
|
|
* which is dead and hence not processing interrupts.
|
|
|
|
*/
|
|
|
|
static void rcu_move_batch(struct rcu_data *this_rdp, struct rcu_head *list,
|
|
|
|
struct rcu_head **tail)
|
|
|
|
{
|
|
|
|
local_irq_disable();
|
|
|
|
*this_rdp->nxttail = list;
|
|
|
|
if (list)
|
|
|
|
this_rdp->nxttail = tail;
|
|
|
|
local_irq_enable();
|
|
|
|
}
|
|
|
|
|
|
|
|
static void __rcu_offline_cpu(struct rcu_data *this_rdp,
|
|
|
|
struct rcu_ctrlblk *rcp, struct rcu_data *rdp)
|
|
|
|
{
|
|
|
|
/* if the cpu going offline owns the grace period
|
|
|
|
* we can block indefinitely waiting for it, so flush
|
|
|
|
* it here
|
|
|
|
*/
|
|
|
|
spin_lock_bh(&rcp->lock);
|
|
|
|
if (rcp->cur != rcp->completed)
|
|
|
|
cpu_quiet(rdp->cpu, rcp);
|
|
|
|
spin_unlock_bh(&rcp->lock);
|
2008-01-25 21:08:24 +01:00
|
|
|
rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail);
|
2008-01-25 21:08:24 +01:00
|
|
|
rcu_move_batch(this_rdp, rdp->curlist, rdp->curtail);
|
|
|
|
rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail);
|
|
|
|
}
|
|
|
|
|
|
|
|
static void rcu_offline_cpu(int cpu)
|
|
|
|
{
|
|
|
|
struct rcu_data *this_rdp = &get_cpu_var(rcu_data);
|
|
|
|
struct rcu_data *this_bh_rdp = &get_cpu_var(rcu_bh_data);
|
|
|
|
|
|
|
|
__rcu_offline_cpu(this_rdp, &rcu_ctrlblk,
|
|
|
|
&per_cpu(rcu_data, cpu));
|
|
|
|
__rcu_offline_cpu(this_bh_rdp, &rcu_bh_ctrlblk,
|
|
|
|
&per_cpu(rcu_bh_data, cpu));
|
|
|
|
put_cpu_var(rcu_data);
|
|
|
|
put_cpu_var(rcu_bh_data);
|
|
|
|
}
|
|
|
|
|
|
|
|
#else
|
|
|
|
|
|
|
|
static void rcu_offline_cpu(int cpu)
|
|
|
|
{
|
|
|
|
}
|
|
|
|
|
|
|
|
#endif
|
|
|
|
|
|
|
|
/*
|
|
|
|
* This does the RCU processing work from softirq context.
|
|
|
|
*/
|
|
|
|
static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
|
|
|
|
struct rcu_data *rdp)
|
|
|
|
{
|
|
|
|
if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch)) {
|
|
|
|
*rdp->donetail = rdp->curlist;
|
|
|
|
rdp->donetail = rdp->curtail;
|
|
|
|
rdp->curlist = NULL;
|
|
|
|
rdp->curtail = &rdp->curlist;
|
|
|
|
}
|
|
|
|
|
|
|
|
if (rdp->nxtlist && !rdp->curlist) {
|
|
|
|
local_irq_disable();
|
|
|
|
rdp->curlist = rdp->nxtlist;
|
|
|
|
rdp->curtail = rdp->nxttail;
|
|
|
|
rdp->nxtlist = NULL;
|
|
|
|
rdp->nxttail = &rdp->nxtlist;
|
|
|
|
local_irq_enable();
|
|
|
|
|
|
|
|
/*
|
|
|
|
* start the next batch of callbacks
|
|
|
|
*/
|
|
|
|
|
|
|
|
/* determine batch number */
|
|
|
|
rdp->batch = rcp->cur + 1;
|
|
|
|
/* see the comment and corresponding wmb() in
|
|
|
|
* the rcu_start_batch()
|
|
|
|
*/
|
|
|
|
smp_rmb();
|
|
|
|
|
|
|
|
if (!rcp->next_pending) {
|
|
|
|
/* and start it/schedule start if it's a new batch */
|
|
|
|
spin_lock(&rcp->lock);
|
|
|
|
rcp->next_pending = 1;
|
|
|
|
rcu_start_batch(rcp);
|
|
|
|
spin_unlock(&rcp->lock);
|
|
|
|
}
|
|
|
|
}
|
|
|
|
|
|
|
|
rcu_check_quiescent_state(rcp, rdp);
|
|
|
|
if (rdp->donelist)
|
|
|
|
rcu_do_batch(rdp);
|
|
|
|
}
|
|
|
|
|
|
|
|
static void rcu_process_callbacks(struct softirq_action *unused)
|
|
|
|
{
|
|
|
|
__rcu_process_callbacks(&rcu_ctrlblk, &__get_cpu_var(rcu_data));
|
|
|
|
__rcu_process_callbacks(&rcu_bh_ctrlblk, &__get_cpu_var(rcu_bh_data));
|
|
|
|
}
|
|
|
|
|
|
|
|
static int __rcu_pending(struct rcu_ctrlblk *rcp, struct rcu_data *rdp)
|
|
|
|
{
|
|
|
|
/* This cpu has pending rcu entries and the grace period
|
|
|
|
* for them has completed.
|
|
|
|
*/
|
|
|
|
if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch))
|
|
|
|
return 1;
|
|
|
|
|
|
|
|
/* This cpu has no pending entries, but there are new entries */
|
|
|
|
if (!rdp->curlist && rdp->nxtlist)
|
|
|
|
return 1;
|
|
|
|
|
|
|
|
/* This cpu has finished callbacks to invoke */
|
|
|
|
if (rdp->donelist)
|
|
|
|
return 1;
|
|
|
|
|
|
|
|
/* The rcu core waits for a quiescent state from the cpu */
|
|
|
|
if (rdp->quiescbatch != rcp->cur || rdp->qs_pending)
|
|
|
|
return 1;
|
|
|
|
|
|
|
|
/* nothing to do */
|
|
|
|
return 0;
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* Check to see if there is any immediate RCU-related work to be done
|
|
|
|
* by the current CPU, returning 1 if so. This function is part of the
|
|
|
|
* RCU implementation; it is -not- an exported member of the RCU API.
|
|
|
|
*/
|
|
|
|
int rcu_pending(int cpu)
|
|
|
|
{
|
|
|
|
return __rcu_pending(&rcu_ctrlblk, &per_cpu(rcu_data, cpu)) ||
|
|
|
|
__rcu_pending(&rcu_bh_ctrlblk, &per_cpu(rcu_bh_data, cpu));
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* Check to see if any future RCU-related work will need to be done
|
|
|
|
* by the current CPU, even if none need be done immediately, returning
|
|
|
|
* 1 if so. This function is part of the RCU implementation; it is -not-
|
|
|
|
* an exported member of the RCU API.
|
|
|
|
*/
|
|
|
|
int rcu_needs_cpu(int cpu)
|
|
|
|
{
|
|
|
|
struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
|
|
|
|
struct rcu_data *rdp_bh = &per_cpu(rcu_bh_data, cpu);
|
|
|
|
|
|
|
|
return (!!rdp->curlist || !!rdp_bh->curlist || rcu_pending(cpu));
|
|
|
|
}
|
|
|
|
|
|
|
|
void rcu_check_callbacks(int cpu, int user)
|
|
|
|
{
|
|
|
|
if (user ||
|
|
|
|
(idle_cpu(cpu) && !in_softirq() &&
|
|
|
|
hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
|
2008-05-12 21:21:05 +02:00
|
|
|
|
|
|
|
/*
|
|
|
|
* Get here if this CPU took its interrupt from user
|
|
|
|
* mode or from the idle loop, and if this is not a
|
|
|
|
* nested interrupt. In this case, the CPU is in
|
|
|
|
* a quiescent state, so count it.
|
|
|
|
*
|
|
|
|
* Also do a memory barrier. This is needed to handle
|
|
|
|
* the case where writes from a preempt-disable section
|
|
|
|
* of code get reordered into schedule() by this CPU's
|
|
|
|
* write buffer. The memory barrier makes sure that
|
|
|
|
* the rcu_qsctr_inc() and rcu_bh_qsctr_inc() are see
|
|
|
|
* by other CPUs to happen after any such write.
|
|
|
|
*/
|
|
|
|
|
|
|
|
smp_mb(); /* See above block comment. */
|
2008-01-25 21:08:24 +01:00
|
|
|
rcu_qsctr_inc(cpu);
|
|
|
|
rcu_bh_qsctr_inc(cpu);
|
2008-05-12 21:21:05 +02:00
|
|
|
|
|
|
|
} else if (!in_softirq()) {
|
|
|
|
|
|
|
|
/*
|
|
|
|
* Get here if this CPU did not take its interrupt from
|
|
|
|
* softirq, in other words, if it is not interrupting
|
|
|
|
* a rcu_bh read-side critical section. This is an _bh
|
|
|
|
* critical section, so count it. The memory barrier
|
|
|
|
* is needed for the same reason as is the above one.
|
|
|
|
*/
|
|
|
|
|
|
|
|
smp_mb(); /* See above block comment. */
|
2008-01-25 21:08:24 +01:00
|
|
|
rcu_bh_qsctr_inc(cpu);
|
2008-05-12 21:21:05 +02:00
|
|
|
}
|
2008-01-25 21:08:24 +01:00
|
|
|
raise_rcu_softirq();
|
|
|
|
}
|
|
|
|
|
|
|
|
static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp,
|
|
|
|
struct rcu_data *rdp)
|
|
|
|
{
|
|
|
|
memset(rdp, 0, sizeof(*rdp));
|
|
|
|
rdp->curtail = &rdp->curlist;
|
|
|
|
rdp->nxttail = &rdp->nxtlist;
|
|
|
|
rdp->donetail = &rdp->donelist;
|
|
|
|
rdp->quiescbatch = rcp->completed;
|
|
|
|
rdp->qs_pending = 0;
|
|
|
|
rdp->cpu = cpu;
|
|
|
|
rdp->blimit = blimit;
|
|
|
|
}
|
|
|
|
|
|
|
|
static void __cpuinit rcu_online_cpu(int cpu)
|
|
|
|
{
|
|
|
|
struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
|
|
|
|
struct rcu_data *bh_rdp = &per_cpu(rcu_bh_data, cpu);
|
|
|
|
|
|
|
|
rcu_init_percpu_data(cpu, &rcu_ctrlblk, rdp);
|
|
|
|
rcu_init_percpu_data(cpu, &rcu_bh_ctrlblk, bh_rdp);
|
|
|
|
open_softirq(RCU_SOFTIRQ, rcu_process_callbacks, NULL);
|
|
|
|
}
|
|
|
|
|
|
|
|
static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
|
|
|
|
unsigned long action, void *hcpu)
|
|
|
|
{
|
|
|
|
long cpu = (long)hcpu;
|
|
|
|
|
|
|
|
switch (action) {
|
|
|
|
case CPU_UP_PREPARE:
|
|
|
|
case CPU_UP_PREPARE_FROZEN:
|
|
|
|
rcu_online_cpu(cpu);
|
|
|
|
break;
|
|
|
|
case CPU_DEAD:
|
|
|
|
case CPU_DEAD_FROZEN:
|
|
|
|
rcu_offline_cpu(cpu);
|
|
|
|
break;
|
|
|
|
default:
|
|
|
|
break;
|
|
|
|
}
|
|
|
|
return NOTIFY_OK;
|
|
|
|
}
|
|
|
|
|
|
|
|
static struct notifier_block __cpuinitdata rcu_nb = {
|
|
|
|
.notifier_call = rcu_cpu_notify,
|
|
|
|
};
|
|
|
|
|
|
|
|
/*
|
|
|
|
* Initializes rcu mechanism. Assumed to be called early.
|
|
|
|
* That is before local timer(SMP) or jiffie timer (uniproc) is setup.
|
|
|
|
* Note that rcu_qsctr and friends are implicitly
|
|
|
|
* initialized due to the choice of ``0'' for RCU_CTR_INVALID.
|
|
|
|
*/
|
|
|
|
void __init __rcu_init(void)
|
|
|
|
{
|
|
|
|
rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE,
|
|
|
|
(void *)(long)smp_processor_id());
|
|
|
|
/* Register notifier for non-boot CPUs */
|
|
|
|
register_cpu_notifier(&rcu_nb);
|
|
|
|
}
|
|
|
|
|
|
|
|
module_param(blimit, int, 0);
|
|
|
|
module_param(qhimark, int, 0);
|
|
|
|
module_param(qlowmark, int, 0);
|