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Re: fs/attr.c:notify_change locking warning.

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: fs/attr.c:notify_change locking warning.
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Wed, 16 Oct 2013 11:12:34 -0700
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>, Dave Jones <davej@xxxxxxxxxx>, xfs@xxxxxxxxxxx, Linux Kernel <linux-kernel@xxxxxxxxxxxxxxx>, Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20131016102651.GF4446@dastard>
References: <20131005005210.GA25773@xxxxxxxxxx> <20131005031918.GL4446@dastard> <20131015201905.GA7509@xxxxxxxxxxxxx> <20131015213618.GU4446@dastard> <20131016070528.GB18721@xxxxxxxxxxxxx> <20131016102651.GF4446@dastard>
User-agent: Mutt/1.5.21 (2010-09-15)
On Wed, Oct 16, 2013 at 09:26:51PM +1100, Dave Chinner wrote:
> The killpriv calls? I couldn't find anything that implemented those
> security hooks nor any documentation about it, so I'm pretty much
> clueless about it. FWIW, ocfs2 doesn't implement them, either....

The killpriv code ends up doing xattr calls for per-file capabilities
(grep security/commoncap.c for killpriv).  Seems like ocfs2 is buggy in
that regard.

I suspect the easiest way to solve it properly in XFS is to simply
retake the iolock exclusive and get the i_mutex as part of it.  This
means direct I/O writes to files with the suid bit won't scale, but I
think we can live with that given that it avoids introducing special
cases that impact more code.

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