netdev - __refrigerator() && saved task->state

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Message-ID: <20131113191143.GA24005@redhat.com>
Date:	Wed, 13 Nov 2013 20:11:43 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	David Rientjes <rientjes@...gle.com>,
	David Laight <David.Laight@...LAB.COM>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Ingo Molnar <mingo@...nel.org>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: __refrigerator() && saved task->state

Sorry for noise, but I am totally confused.

Could you please remind why __refrigerator() saves/restores
task->state?

I can see only one reason: set_freezable() kernel threads which
check kthread_should_stop() and do try_to_freeze() by hand.

But does this save/restore actually help?

For example kauditd_thread() looks obviously racy exactly because
try_to_freeze() can return in TASK_INTERRUPTIBLE state after
wake_up(kauditd_wait) was already called, we can miss an event.

At first glance it would be better to simply kill this logic? If
it was called with ->state != 0, the caller is going to schedule()
and it probably executes the wait_event-like code, in this case
it would me more safe to pretend the task got a spurious wakeup?

(as for kauditd_thread() in particular, it looks wrong in any
 case, even kthread_should_stop() check doesn't look right, it
 needs kthread_freezable_should_stop() afaics).

But I guess I missed something else...

Oleg.

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