linux-kernel - Re: [PATCH] remove BUG() in possible but rare condition

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Message-ID: <20120411192554.GC24831@tiehlicka.suse.cz>
Date:	Wed, 11 Apr 2012 21:25:54 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Glauber Costa <glommer@...allels.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, devel@...nvz.org, linux-mm@...ck.org,
	cgroups@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
	kamezawa.hiroyu@...fujitsu.com, Greg Thelen <gthelen@...gle.com>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] remove BUG() in possible but rare condition

On Wed 11-04-12 16:02:19, Glauber Costa wrote:
> On 04/11/2012 03:57 PM, Linus Torvalds wrote:
> >On Wed, Apr 11, 2012 at 11:48 AM, Michal Hocko<mhocko@...e.cz>  wrote:
> >>
> >>I am not familiar with the code much but a trivial call chain walk up to
> >>write_dev_supers (in btrfs) shows that we do not check for the return value
> >>from __getblk so we would nullptr and there might be more.
> >>I guess these need some treat before the BUG might be removed, right?
> >
> >Well, realistically, isn't BUG() as bad as a NULL pointer dereference?
> >
> >Do you care about the exact message on the screen when your machine dies?
> Not particular, but I don't see why (I might be wrong) it would
> necessarily lead to a NULL pointer dereference.

Ahh, OK scratch that. I have misread __getblk_slow which returns NULL
only if grow_buffers returned with < 0 which doesn't happen for the
allocation failure.

Sorry about noise
-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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