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

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Message-ID: <20080109184814.GA1562@infradead.org>
Date:	Wed, 9 Jan 2008 18:48:14 +0000
From:	Christoph Hellwig <hch@...radead.org>
To:	Jeff Layton <jlayton@...hat.com>
Cc:	Christoph Hellwig <hch@...radead.org>, 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, 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?
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