linux-kernel - [PATCH 11/14] trace: Fix invalid wakeup in wait_to

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Date:	Thu, 29 Aug 2013 21:57:46 +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 11/14] trace: Fix invalid wakeup in wait_to_die

If thread is preempted before calling set_current_state(TASK_INTERRUPTIBLE),
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.
-------------
wait_to_die()
-------------
set_current_state(TASK_INTERRUPTIBLE);
while (!kthread_should_stop()) {
	schedule();
	set_current_state(TASK_INTERRUPTIBLE);
}
__set_current_state(TASK_RUNNING);

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.
-------------
wait_to_die()
-------------
preempt_disable();
set_current_state(TASK_INTERRUPTIBLE);
while (!kthread_should_stop()) {
	preempt_enable();
	schedule();
	preempt_disable();
	set_current_state(TASK_INTERRUPTIBLE);
}
__set_current_state(TASK_RUNNING);
preempt_enable();

Signed-off-by: Libin <huawei.libin@...wei.com>
---
 kernel/trace/ring_buffer_benchmark.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/trace/ring_buffer_benchmark.c b/kernel/trace/ring_buffer_benchmark.c
index a5457d5..3c0bc03 100644
--- a/kernel/trace/ring_buffer_benchmark.c
+++ b/kernel/trace/ring_buffer_benchmark.c
@@ -359,12 +359,16 @@ static void ring_buffer_producer(void)
 
 static void wait_to_die(void)
 {
+	preempt_disable();
 	set_current_state(TASK_INTERRUPTIBLE);
 	while (!kthread_should_stop()) {
+		preempt_enable();
 		schedule();
+		preempt_disable();
 		set_current_state(TASK_INTERRUPTIBLE);
 	}
 	__set_current_state(TASK_RUNNING);
+	preempt_enable();
 }
 
 static int ring_buffer_consumer_thread(void *arg)
-- 
1.8.2.1


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