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

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Message-ID: <20110107215904.GQ21922@thunk.org>
Date:	Fri, 7 Jan 2011 16:59:04 -0500
From:	Ted Ts'o <tytso@....edu>
To:	Jan Kara <jack@...e.cz>
Cc:	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 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.

Thanks,

	      	      	  	     	 - Ted


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