linux-kernel - Re: [PATCH 04/14] mm,migration: Allow the migration of PageSwapCache pages

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sat, 24 Apr 2010 11:52:27 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	Minchan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 04/14] mm,migration: Allow the migration of
	PageSwapCache  pages

On Fri, Apr 23, 2010 at 11:35:49PM +0200, Andrea Arcangeli wrote:
> On Fri, Apr 23, 2010 at 09:39:48PM +0200, Andrea Arcangeli wrote:
> > On Fri, Apr 23, 2010 at 08:23:12PM +0100, Mel Gorman wrote:
> > > On Fri, Apr 23, 2010 at 08:31:35PM +0200, Andrea Arcangeli wrote:
> > > > Hi Mel,
> > > > 
> > > > On Thu, Apr 22, 2010 at 04:44:43PM +0100, Mel Gorman wrote:
> > > > > heh, I thought of a similar approach at the same time as you but missed
> > > > > this mail until later. However, with this approach I suspect there is a
> > > > > possibility that two walkers of the same anon_vma list could livelock if
> > > > > two locks on the list are held at the same time. Am still thinking of
> > > > > how it could be resolved without introducing new locking.
> > > > 
> > > > Trying to understand this issue and I've some questions. This
> > > > vma_adjust and lock inversion troubles with the anon-vma lock in
> > > > rmap_walk are a new issue introduced by the recent anon-vma changes,
> > > > right?
> > > > 
> > > 
> > > In a manner of speaking. There was no locking going on but prior to the
> > > anon_vma changes, there would have been only one anon_vma lock and the
> > > fix would be easier - just take the lock on anon_vma->lock while the
> > > VMAs are being updated.
> > 
> > So it was very much a bug before too and we could miss to find some
> > pte mapping the page if vm_start was adjusted?
> 
> Well I looked deeper into it myself as I wanted to have this bit (and
> other bits) sorted out in aa.git, and definitely this is a bug
> introduced by the newest anon-vma changes in 2.6.34-rc so aa.git
> cannot be affected as it's using the 2.6.33 anon-vma (and prev) code.
> 

I think you're right. This is a new bug introduced by the anon_vma changes. On
the plus side, it means we don't have to worry about -stable.

> vma_adjust already takes the anon_vma->lock and of course I also
> further verified that trying to apply your snippet to vma_adjust
> results in immediately deadlock as the very same lock is already taken
> in my tree as it's the same anon-vma (simpler).

Yes, I expected that. Previously, there was only one anon_vma so if you
double-take the lock, bad things happen.

> So aa.git will be
> immune from these bugs for now.
> 

It should be. I expect that's why you have never seen the bugon in
swapops.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/