linux-kernel - Re: 3.15-rc8 mm/filemap.c:202 BUG

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Date:	Fri, 06 Jun 2014 19:21:52 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	Dave Jones <davej@...hat.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: 3.15-rc8 mm/filemap.c:202 BUG

On 06/06/2014 07:16 PM, Linus Torvalds wrote:
>> I have no evidence that its lack is responsible for the mm/filemap.c:202
>> > BUG_ON(page_mapped(page)) in __delete_from_page_cache() found by trinity,
>> > and I am not optimistic that it will fix it.  But I have found no other
>> > explanation, and ACCESS_ONCE() here will surely not hurt.
> The patch looks obviously correct to me, although like you, I have no
> real reason to believe it really fixes anything. But we definitely
> should just load it once, since it's very much an optimistic load done
> before we take the real lock and re-compare.
> 
> I'm somewhat dubious whether it actually would change code generation
> - it doesn't change anything with the test-configuration I tried with
> - but it's unquestionably a good patch. And hey, maybe some
> configurations have sufficiently different code generation that gcc
> actually _can_ sometimes do reloads, perhaps explaining why some
> people see problems. So it's certainly worth testing even if it
> doesn't make any change to code generation with *my* compiler and
> config..

I'm seeing the same code generated here as well. I won't carry the
patch unless Andrew/Linus take it so it won't hide possible bugs that
trinity might stumble on.


Thanks,
Sasha
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