[PATCH 09/14] rcutree: Fix invalid wakeup in rcu_wait

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

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@huawei.com>
---
 kernel/rcutree.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index b383258..e3f1278 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -357,13 +357,17 @@ struct rcu_data {
 
 #define rcu_wait(cond)							\
 do {									\
+	preempt_disable();					\
 	for (;;) {							\
 		set_current_state(TASK_INTERRUPTIBLE);			\
 		if (cond)						\
 			break;						\
+		preempt_enable();				\
 		schedule();						\
+		preempt_disable();				\
 	}								\
 	__set_current_state(TASK_RUNNING);				\
+	preempt_enable();				\
 } while (0)
 
 /*
-- 
1.8.2.1