[PATCH 02/14] audit: Fix invalid wakeup in kauditd_thread

[Libin <huawei.libin@huawei.com>]

If this thread is preempted at(or before) location a, 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.
----------------
kauditd_thread()
----------------
while (!kthread_should_stop()) {
	...
		//location a
		set_current_state(TASK_INTERRUPTIBLE);
	...

		if (!skb_queue_len(&audit_skb_queue)) {
			//location b
			try_to_freeze();
			schedule();
			//location c
		}

	__set_current_state(TASK_RUNNING);
	//location d
	...
}

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.
----------------
kauditd_thread()
----------------
while (!kthread_should_stop()) {
	...
		preempt_disable();
	set_current_state(TASK_INTERRUPTIBLE);
	...

		if (!skb_queue_len(&audit_skb_queue)) {
			preempt_enable();
			try_to_freeze();
			schedule();
			preempt_disable();
		}

	__set_current_state(TASK_RUNNING);
	preempt_enable();
	...
}

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

diff --git a/kernel/audit.c b/kernel/audit.c
index 91e53d0..a7d1346 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -455,15 +455,19 @@ static int kauditd_thread(void *dummy)
 				audit_printk_skb(skb);
 			continue;
 		}
+		preempt_disable();
 		set_current_state(TASK_INTERRUPTIBLE);
 		add_wait_queue(&kauditd_wait, &wait);
 
 		if (!skb_queue_len(&audit_skb_queue)) {
+			preempt_enable();
 			try_to_freeze();
 			schedule();
+			preempt_disable();
 		}
 
 		__set_current_state(TASK_RUNNING);
+		preempt_enable();
 		remove_wait_queue(&kauditd_wait, &wait);
 	}
 	return 0;
-- 
1.8.2.1