linux-kernel - Re: [PATCH 1/1] freezer: fix wait_event_freezable/__thaw

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Date:	Thu, 8 Sep 2011 10:05:30 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, matthltc@...ibm.com,
	paul@...lmenage.org, containers@...ts.linux-foundation.org,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] freezer: fix wait_event_freezable/__thaw_task races

Hello,

On Wed, Sep 07, 2011 at 08:22:17PM +0200, Oleg Nesterov wrote:
> wait_event_freezable() and wait_event_freezable_timeout() stop
> the waiting if try_to_freeze() fails. This is not right, we can
> race with __thaw_task() and in this case
> 
> 	- wait_event_freezable() returns the wrong ERESTARTSYS
> 
> 	- wait_event_freezable_timeout() can return the positive
> 	  value while condition == F

Indeed, nice catch.  This one actually is pretty dangerous.  We
probably want to make a separate fix for this and backport it to
-stable?

> Change the code to always check __retval/condition before return.
> 
> Note: with or without this patch the timeout logic looks strange,
> probably we should recalc timeout if try_to_freeze() returns T.
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Yeap, with freezable_with_signal gone, this looks correct & simpler to
me but it would be nice if you can sprinkle some documentation while
at it. :)

Thanks.

-- 
tejun
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