Re: VFS deadlock ?

From: Al Viro
Date: Thu Mar 21 2013 - 20:13:05 EST

On Thu, Mar 21, 2013 at 05:01:49PM -0700, Linus Torvalds wrote:
> On Thu, Mar 21, 2013 at 4:58 PM, Linus Torvalds
> <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> >
> > So yes, it's against the rules, and we get that deadlock right now,
> > but one solution would be to just allow this particular case. The
> > patch for the deadlock looks dead simple:
> It should go without saying that that whitespace-damaged patch is
> entirely untested. But especially since we need to back-port whatever
> fix, it would be good if we could make the fix be something as simple
> as this. Because I don't believe we really want to backport some big
> network-namespace reorganization.
> This is, of course, all assuming that hardlinked directories are ok if
> we can just guarantee the absence of loops. If there's some other
> reason why they'd be problematic, we're screwed.

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
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