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Date: Fri, 22 Mar 2013 00:20:31 +0000
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Dave Jones <davej@redhat.com>, Linux Kernel <linux-kernel@vger.kernel.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>
Subject: Re: VFS deadlock ?
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On Fri, Mar 22, 2013 at 12:12:57AM +0000, Al Viro wrote:

> See the posting upthread.  We could try to kludge around that as well
> (e.g. have d_ancestor() compare ->d_inode instead of dentries themselves),
> but I really think it's a lousy idea only inviting further abuse.
> 
> What we should do, IMO, is to turn /proc/<pid>/net into a honest symlink -
> to ../nets/<netns ID>/net.  Hell, might even make it a magical symlink
> instead...

BTW, the root cause is that what used to be /proc/net became per-process.
So Eric (IIRC) had added /proc/<pid>/net.  Only they are not really per-process
- they are per-netns.  And instead of putting those per-ns trees elsewhere and
having /proc/<pid>/net resolve to the right one, we got them as directories,
with each entry hardlinked between all /proc/<pid>/net for processes from
the same netns.  Including the subdirectory ones.  Oops...

Another variant is to keep cross-hardlinks for non-directories and duplicate
directory dentries/inodes as we do for /proc/<pid>/net themselves.
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