linux-kernel - [PATCH 12/14] trace: Fix invalid wakeup in ring_buffer_consumer

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Date:	Thu, 29 Aug 2013 21:57:47 +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 12/14] trace: Fix invalid wakeup in ring_buffer_consumer_thread

If thread is preempted before calling set_current_state(TASK_INTERRUPTIBLE),
and the other thread set the condition followed with wake_up_process. 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.

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/trace/ring_buffer_benchmark.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/kernel/trace/ring_buffer_benchmark.c b/kernel/trace/ring_buffer_benchmark.c
index 3c0bc03..4f43a96 100644
--- a/kernel/trace/ring_buffer_benchmark.c
+++ b/kernel/trace/ring_buffer_benchmark.c
@@ -172,6 +172,9 @@ static enum event_status read_page(int cpu)
 	return EVENT_FOUND;
 }
 
+/*
+ * Called in preemptation disabled environment.
+ */
 static void ring_buffer_consumer(void)
 {
 	/* toggle between reading pages and events */
@@ -204,9 +207,12 @@ static void ring_buffer_consumer(void)
 		if (reader_finish)
 			break;
 
+		preempt_enable();
 		schedule();
 		__set_current_state(TASK_RUNNING);
+		preempt_disable();
 	}
+
 	reader_finish = 0;
 	complete(&read_done);
 }
@@ -373,6 +379,7 @@ static void wait_to_die(void)
 
 static int ring_buffer_consumer_thread(void *arg)
 {
+	preempt_disable();
 	while (!kthread_should_stop() && !kill_test) {
 		complete(&read_start);
 
@@ -382,10 +389,13 @@ static int ring_buffer_consumer_thread(void *arg)
 		if (kthread_should_stop() || kill_test)
 			break;
 
+		preempt_enable();
 		schedule();
 		__set_current_state(TASK_RUNNING);
+		preempt_disable();
 	}
 	__set_current_state(TASK_RUNNING);
+	preempt_enable();
 
 	if (kill_test)
 		wait_to_die();
-- 
1.8.2.1


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