linux-ext4 - Re: [PATCH] quota: Fix deadlock during path resolution

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Message-ID: <20110112180611.GA14260@quack.suse.cz>
Date:	Wed, 12 Jan 2011 19:06:11 +0100
From:	Jan Kara <jack@...e.cz>
To:	Ted Ts'o <tytso@....edu>
Cc:	Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@....de>,
	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
	reiserfs-devel@...r.kernel.org, ocfs2-devel@....oracle.com,
	Al Viro <viro@...IV.linux.org.uk>,
	Joel Becker <joel.becker@...cle.com>
Subject: Re: [PATCH] quota: Fix deadlock during path resolution

On Fri 07-01-11 16:59:04, Ted Ts'o wrote:
> On Thu, Sep 16, 2010 at 11:55:53AM +0200, Jan Kara wrote:
> > On Thu 16-09-10 00:52:08, Christoph Hellwig wrote:
> > > On Wed, Sep 15, 2010 at 11:39:51PM +0200, Jan Kara wrote:
> > > > As Al Viro pointed out path resolution during Q_QUOTAON calls to quotactl
> > > > is prone to deadlocks. We hold s_umount semaphore for reading during the
> > > > path resolution and resolution itself may need to acquire the semaphore
> > > > for writing when e. g. autofs mountpoint is passed.
> > > > 
> > > > Solve the problem by performing the resolution before we get hold of the
> > > > superblock (and thus s_umount semaphore). The whole thing is complicated
> > > > by the fact that some filesystems (OCFS2) ignore the path argument. So to
> > > > distinguish between filesystem which want the path and which do not we
> > > > introduce new .quota_on_meta callback which does not get the path. OCFS2
> > > > then uses this callback instead of old .quota_on.
> > > 
> > > FYI I have a patch that switches ocfs to share the quota_on method with
> > > XFS which behaves the same, and consolidate the quota_off method for all
> > > filesystems.  I think that's better than adding yet another method.
> > > 
> > > I'll rebase it and send it out soon.
> >   Ok, that would be nice. I'll wait with my fix then.
> 
> I was going through my ext4 patch backlog, and came across this patch
> 
> 	http://patchwork.ozlabs.org/patch/64910/
> 
> Did anything ever happen with Christoph's ocfs2 quota patch, which he
> was going to rebase?  I took a quick gander in git and I didn't see
> anything, but maybe I was looking in the wrong place.
  As Christoph wrote, we agreed to push my fix in the end. I've sent it
to Al twice but sifting through his tree now, he doesn't seem to have it
in. So I'll push the change via my tree for rc1 (if I still manage to get
it in) or rc2. Thanks for reminder.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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