linux-kernel - Re: [PATCH pm-freezer 1/4] cgroup_freezer: fix freezer->state setting bug in freezer_change

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Date:	Sat, 3 Sep 2011 02:08:44 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Matt Helsley <matthltc@...ibm.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Paul Menage <paul@...lmenage.org>,
	containers@...ts.linux-foundation.org,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH pm-freezer 1/4] cgroup_freezer: fix freezer->state
 setting bug in freezer_change_state()

Hello,

On Fri, Sep 02, 2011 at 06:58:39PM +0200, Oleg Nesterov wrote:
> > This still doesn't look quite right. If the cgroup is FREEZING it should
> > also call try_to_freeze_cgroup(). I think this is what's needed:
> >
> > 		if (freezer->state == CGROUP_THAWED)
> > 			atomic_inc(&system_freezing_cnt);
> > 		freezer->state = CGROUP_FREEZING;
> > 		retval = try_to_freeze_cgroup(cgroup, freezer);
> 
> This is what I mentioned before, to me this looks like a win.
> 
> Why do we need try_to_freeze_cgroup() in this case? "for safety"
> could actually mean "hide the bug" ;)

I guess it depends on the viewpoint.  A simple analogy would be using
WARN_ON_ONCE() instead of BUG_ON() so that the mode of failure is
softer.  This change isn't likely to make bugs significantly more
difficult to discover so why not?

> But I agree either way. Rafael, I think 1-4 are fine, but I think
> we need the simple 5/4, will send in a minute...

Can you please wait a bit?  The second one was broken (missing unlock)
and I made some small adjustments.  Will repost soon.

Thanks.

-- 
tejun
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