linux-kernel - [PATCH 06/14] irq: Fix invalid wakeup in irq_wait_for

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Date:	Thu, 29 Aug 2013 21:57:41 +0800
From:	Libin <huawei.libin@...wei.com>
To:	<akpm@...ux-foundation.org>, <tj@...nel.org>,
	<viro@...iv.linux.org.uk>, <eparis@...hat.com>,
	<tglx@...utronix.de>, <rusty@...tcorp.com.au>,
	<ebiederm@...ssion.com>, <paulmck@...ux.vnet.ibm.com>,
	<john.stultz@...aro.org>, <mingo@...hat.com>,
	<peterz@...radead.org>, <gregkh@...uxfoundation.org>
CC:	<linux-kernel@...r.kernel.org>, <lizefan@...wei.com>,
	<jovi.zhangwei@...wei.com>, <guohanjun@...wei.com>,
	<zhangdianfang@...wei.com>, <wangyijing@...wei.com>,
	<huawei.libin@...wei.com>
Subject: [PATCH 06/14] irq: Fix invalid wakeup in irq_wait_for_interrupt

If this thread is preempted at(or before) location a, and the other thread
set the condition(kthread_stop). After that when this thread is re-scheduled,
calling set_current_state to set itself as state TASK_INTERRUPTIBLE, if it is
preempted again after that and before __set_current_state(TASK_RUNNING), it
triggers the invalid wakeup problem.
-----------------------
irq_wait_for_interrupt()
-----------------------
...
//location a
set_current_state(TASK_INTERRUPTIBLE);
//location b
while (!kthread_should_stop()) {

	if (test_and_clear_bit(IRQTF_RUNTHREAD,
					   &action->thread_flags)) {
			__set_current_state(TASK_RUNNING);
			return 0;
	}
	schedule();//location c
	set_current_state(TASK_INTERRUPTIBLE);
	//location d
}
__set_current_state(TASK_RUNNING);
...

The following circumstance will also trigger this issue:
At location c, consumer is scheduled out, and be preempted after calling
set_current_state(TASK_INTERRUPTIBLE) when it be re-schdeuled.

To solve this problem, using preempt_disable() to bound the operaion that
setting the task state and the conditions(set by the wake thread) validation.

Signed-off-by: Libin <huawei.libin@...wei.com>
---
 kernel/irq/manage.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 514bcfd..09cb02f 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -655,6 +655,7 @@ static irqreturn_t irq_nested_primary_handler(int irq, void *dev_id)
 
 static int irq_wait_for_interrupt(struct irqaction *action)
 {
+	preempt_disable();
 	set_current_state(TASK_INTERRUPTIBLE);
 
 	while (!kthread_should_stop()) {
@@ -662,12 +663,16 @@ static int irq_wait_for_interrupt(struct irqaction *action)
 		if (test_and_clear_bit(IRQTF_RUNTHREAD,
 				       &action->thread_flags)) {
 			__set_current_state(TASK_RUNNING);
+			preempt_enable();
 			return 0;
 		}
+		preempt_enable();
 		schedule();
+		preempt_disable();
 		set_current_state(TASK_INTERRUPTIBLE);
 	}
 	__set_current_state(TASK_RUNNING);
+	preempt_enable();
 	return -1;
 }
 
-- 
1.8.2.1


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