linux-kernel - wait_event()\wake

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Date:	Thu, 16 Jun 2016 18:19:17 +0530
From:	Muni Sekhar <munisekharrms@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: wait_event()\wake_up order fails?

Hi All,

I have a kernel thread THREAD_A and it waits for an event by calling
wait_event() API.

Other thread THREAD_B wakes up the THREAD_A by calling wake_up() API.

In a concurrent execution, what if the wake_up() is called before
THREAD_A entering into TASK_UNINTERRUPTIBLE sleep?

I have noticed in running long soak test, THREAD_A enters into
TASK_UNINTERRUPTIBLE sleep and THREAD_B’s wake_up() not able to wake
the THREAD_A, what might be the reason for this?

I would like to know in which scenario wake_up() fails to wake the
sleeping thread?

-- 
Thanks,
Sekhar