linux-kernel - Re: Union mount and lockdep design issues

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Date:	Wed, 13 Jul 2011 13:02:05 +0100
From:	David Howells <dhowells@...hat.com>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	dhowells@...hat.com, Michal Suchanek <hramrach@...trum.cz>,
	Ian Kent <ikent@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ric Wheeler <rwheeler@...hat.com>,
	Alexander Viro <aviro@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Ingo Molnar <mingo@...e.hu>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, Jeff Moyer <jmoyer@...hat.com>
Subject: Re: Union mount and lockdep design issues

Miklos Szeredi <miklos@...redi.hu> wrote:

> Overlayfs never locks both upper and lower at the same time, which means
> there's no AB-BA locking dependency.  The lock orderings are:

What you're talking about is not analogous to the situation I'm seeing with
unionmount.

You actually have three filesystems in overlayfs.  The interaction between
overlayfs-and-upperfs and overlayfs-and-lowerfs is the equivalent in
unionmount terms to upperfs-and-lowerfs.  This is where the lockdep issue
lies.

David
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