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

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Message-ID: <4F85EEED.1090906@parallels.com>
Date:	Wed, 11 Apr 2012 17:51:57 -0300
From:	Glauber Costa <glommer@...allels.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	<linux-kernel@...r.kernel.org>, <devel@...nvz.org>,
	<linux-mm@...ck.org>, <cgroups@...r.kernel.org>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	<kamezawa.hiroyu@...fujitsu.com>, Greg Thelen <gthelen@...gle.com>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] remove BUG() in possible but rare condition

On 04/11/2012 05:26 PM, Andrew Morton wrote:
>>
>> >    failed:
>> >  -	BUG();
>> >    	unlock_page(page);
>> >    	page_cache_release(page);
>> >    	return NULL;
> Cute.
>
> AFAICT what happened was that in my April 2002 rewrite of this code I
> put a non-fatal buffer_error() warning in that case to tell us that
> something bad happened.
>
> Years later we removed the temporary buffer_error() and mistakenly
> replaced that warning with a BUG().  Only it*can*  happen.
>
> We can remove the BUG() and fix up callers, or we can pass retry=1 into
> alloc_page_buffers(), so grow_dev_page() "cannot fail".  Immortal
> functions are a silly fiction, so we should remove the BUG() and fix up
> callers.
>
Any particular caller you are concerned with ?

As I mentioned, this function already returns NULL for other reason - 
that seem even more probable than this specific failure. So whoever is
not checking this return value, is already broken without this patch as 
well.


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