linux-kernel - Re: [PATCH 6/6] NLM: Add reference counting to lockd

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Message-ID: <20080109135920.70eb82cb@tleilax.poochiereds.net>
Date:	Wed, 9 Jan 2008 13:59:20 -0500
From:	Jeff Layton <jlayton@...hat.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	akpm@...ux-foundation.org, neilb@...e.de,
	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/6] NLM: Add reference counting to lockd

On Wed, 9 Jan 2008 18:48:14 +0000
Christoph Hellwig <hch@...radead.org> wrote:

> On Wed, Jan 09, 2008 at 01:36:21PM -0500, Jeff Layton wrote:
> > I don't see a good alternative though. We need to be able to drop
> > the and check the refcount in nlmsvc_unlink_block. That function is
> > called from lockd, and we can't have lockd call kthread_stop on
> > itself.
> > 
> > If you see a better way to do this, I'm certainly open to
> > suggestions.
> > 
> > I'll note that my first stab at fixing this problem was to change
> > the svc_wake_up() call in the rpc callback to a routine to wake up
> > any lockd on the box that happened to be up. That sidesteps this
> > entire problem of having to make sure lockd stays up. If we decided
> > that was the right approach we could dump the last patch in this
> > series altogether.
> > 
> > That said there could be other use after free bugs lurking in the
> > lockd code so maybe keeping lockd up until nlm_blocked is empty is
> > the right thing to do.
> 
> What about just not exiting from lockd as long as nlm_blocked is not
> empty?  lockd_down still simply calls kthread_stop, but lockd only
> honours it when nlm_blocked is empty?

lockd can basically block forever in this situation if the client
goes away for good. With the current kthread implementation,
kthread_stops are serialized and I don't think we want to monopolize
the kthread_stop queue.

If kthread_stops could occur in parallel, that would be a different
situation :-)

-- 
Jeff Layton <jlayton@...hat.com>
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