[PATCH 14/14] klist: Fix invalid wakeup in klist_remove

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

If thread is preempted before calling set_current_state(TASK_UNINTERRUPTIBLE),
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_UNINTERRUPTIBLE, if it is preempted again after that and before
__set_current_state(TASK_RUNNING), it triggers the invalid wakeup problem.
--------------
klist_remove()
--------------
...
for (;;) {
	set_current_state(TASK_UNINTERRUPTIBLE);
	if (waiter.woken)
		break;
	schedule();
}
__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.
--------------
klist_remove()
--------------
...
preempt_disable();
for (;;) {
	set_current_state(TASK_UNINTERRUPTIBLE);
	if (waiter.woken)
		break;
	preempt_enable();
	schedule();
	preempt_disable();
}
__set_current_state(TASK_RUNNING);
preempt_enable();
...

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

diff --git a/lib/klist.c b/lib/klist.c
index 358a368..e7c7208 100644
--- a/lib/klist.c
+++ b/lib/klist.c
@@ -249,13 +249,17 @@ void klist_remove(struct klist_node *n)
 
 	klist_del(n);
 
+	preempt_disable();
 	for (;;) {
 		set_current_state(TASK_UNINTERRUPTIBLE);
 		if (waiter.woken)
 			break;
+		preempt_enable();
 		schedule();
+		preempt_disable();
 	}
 	__set_current_state(TASK_RUNNING);
+	preempt_enable();
 }
 EXPORT_SYMBOL_GPL(klist_remove);
 
-- 
1.8.2.1