In case this was missed, re-posting here.
Haven't found the message Daniel referenced, so don't know if it is
something XFS is doing to trigger this race condition or not.
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From: Daniel Phillips <phillips@xxxxxxxx>
To: Andrew Morton <akpm@xxxxxxxxxx>
Subject: Re: MM patches against 2.5.31
Date: Thu, 29 Aug 2002 00:57:06 +0200
X-Mailer: KMail [version 1.3.2]
Cc: Christian Ehrhardt <ehrhardt@xxxxxxxxxxxxxxxxxxxxx>, lkml
<linux-kernel@xxxxxxxxxxxxxxx>, "linux-mm@xxxxxxxxx" <linux-mm@xxxxxxxxx>
References: <3D644C70.6D100EA5@xxxxxxxxxx> <E17kAvf-0002tx-00@starship>
On Thursday 29 August 2002 00:39, Andrew Morton wrote:
> Daniel Phillips wrote:
> > ...
> > So there's no question that the race is lurking in 2.4. I noticed several
> > more paths besides the one above that look suspicious as well. The bottom
> > line is, 2.4 needs a fix along the lines of my suggestion or Christian's,
> > something that can actually be proved.
> > It's a wonder that this problem manifests so rarely in practice.
> I sort-of glanced through the 2.4 paths and it appears that in all of the
> places where it could do a page_cache_get/release, that would never happen
> because of other parts of the page state.
> Like: it can't be in pagecache, so we won't run writepage, and
> it can't have buffers, so we won't run try_to_release_page().
> Of course, I might have missed a path. And, well, generally: ugh.
I think it is happening. I just went sifting searching through the archives
on 'oops' and '2.4'. The first one I found was:
2.4.18-xfs (xfs related?) oops report
which fits the description nicely.
The race I showed actually causes the page->count to go negative, avoiding
a double free on a technicality. That doesn't make me feel much better about
it. Have you got a BUG_ON(!page_count(page)) in put_page_testzero? I think
we might see some action.
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