Date: Sun, 1 Dec 2013 10:44:22 -0500
From: Jeff Layton <jlayton@redhat.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: linux-nfs@vger.kernel.org, viro@zeniv.linux.org.uk,
        linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 00/11] [RFC] repair net namespace damage to rpc_pipefs
Message-ID: <20131201104422.64a8c7a0@tlielax.poochiereds.net>
In-Reply-To: <20131201131441.790963326@bombadil.infradead.org>
References: <20131201131441.790963326@bombadil.infradead.org>
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Sender: linux-nfs-owner@vger.kernel.org

On Sun, 01 Dec 2013 05:14:41 -0800
Christoph Hellwig <hch@infradead.org> wrote:

> This series tries to get rid of the damage created by sprinkling the
> network namespace cat poo all over rpc_pipefs and users.
> 
> Instead of getting lost in a maze of notifiers and infrastructure build
> around it a cargo cult manner we revert to a slightly nicer version of
> the pre-namespace API.
> 
> To do this we just have to create an in-kernel instance of rpc_pipefs
> that is mounted at network namespace creation so that all functions can
> operated on it.
> 
> As-is this has one major downside: because the initial mount already grabs
> a reference to the network namespace we'll create a cyclic reference and
> will never free the network namespace.  To get around this we'd need
> some way to only grab it once user mounts show up / disapear in the VFS.
> 
> Given that the namespace kraken has infected various internal filesystem
> and will get more soon I suspect this problem is or will become generic
> and will need a proper solution anyway.  Al, any good ideas how to deal
> with this?  Most straight forward way would be to add a counter of
> user vfsmount to the superblock and methods when it goes to 1 and 0,
> but that seems a bit ugly.

I see what you mean here...hrm...

One possibility (though it may have holes that I don't see right
offhand):

Don't call get_ns in rpc_fill_super. Do it in rpc_mount instead, and
only take the reference if MS_KERNMOUNT isn't set?
-- 
Jeff Layton <jlayton@redhat.com>