linux-kernel - Re: [PATCH v2 1/1] hugepages: Fix race between hugetlbfs umount and quota update.

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Date:	Mon, 17 Oct 2011 16:14:45 +1100
From:	David Gibson <david@...son.dropbear.id.au>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Paul Mackerras <paulus@...ba.org>, Andrew Barry <abarry@...y.com>,
	linux-mm <linux-mm@...ck.org>, Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>, Hugh Dickins <hughd@...gle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Hastings <abh@...y.com>
Subject: Re: [PATCH v2 1/1] hugepages: Fix race between hugetlbfs umount and
 quota update.

On Fri, Oct 14, 2011 at 01:59:48PM -0700, Andrew Morton wrote:
> On Wed, 12 Oct 2011 15:43:17 +1100
> Paul Mackerras <paulus@...ba.org> wrote:
> 
> > In the meantime we have a user-triggerable kernel crash.  As far as I
> > can see, if we did what you suggest, we would end up with a situation
> > where we could run out of huge pages even though everyone was within
> > quota.  Which is arguably better than a kernel crash, but still less
> > than ideal.  What do you suggest?
> 
> My issue with the patch is that it's rather horrible.  We have a layer
> of separation between core hugetlb pages and hugetlbfs.  That layering
> has already been mucked up in various places and this patch mucks it up
> further, and quite severely.
> 
> So I believe we should rethink the patch.  Either a) get the layering
> correct by not poking into hugetlbfs internals from within hugetlb core
> via one of the usual techniques or

Which usual techniques did you have in mind?

> b) make a deliberate decision to
> just give up on that layering: state that hugetlb and hugetlbfs are now
> part of the same subsystem.  Make the necessaary Kconfig changes,
> remove ifdefs, move code around, etc.

Well, that might have something to be said for it, the distinction has
always been tenuous at best.

> If we go ahead with the proposed patch-n-run bugfix, the bad code will
> be there permanently - nobody will go in and clean this mess up and the
> kernel is permanently worsened.

Hrm, as opposed to leaving the crash bug there until someone has time
to do the requested cleanup.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson
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