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

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Date:	Wed, 11 Apr 2012 16:02:19 -0300
From:	Glauber Costa <glommer@...allels.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Michal Hocko <mhocko@...e.cz>, <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 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.

At least in my test cases, after turning this to a WARN (to make sure it 
was still being hit), the machine could go on just fine.

I was running this in a container system, with restricted memory. After
killing the container - at least in my ext4 system - everything seemed 
as happy as ever.

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