Re: [PATCH 00/11] [RFC] repair net namespace damage to rpc_pipefs

[Jeff Layton <jlayton-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On Sun, 01 Dec 2013 05:14:41 -0800
Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.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-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
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