linux-kernel - Re: [PATCH] nfs: fix bdi_unregister() before sb kill

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Message-ID: <20090917194802.GT23126@kernel.dk>
Date:	Thu, 17 Sep 2009 21:48:03 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	trond.myklebust@....uio.no
Subject: Re: [PATCH] nfs: fix bdi_unregister() before sb kill

On Thu, Sep 17 2009, Peter Zijlstra wrote:
> On Thu, 2009-09-17 at 21:40 +0200, Jens Axboe wrote:
> > On Thu, Sep 17 2009, Jens Axboe wrote:
> > > Hi,
> > > 
> > > This can cause a hang on NFS umount, since the bdi gets pruned before we
> > > flush any pending dirty IO. Peter, can you check whether it fixes your
> > > issue?
> > 
> > There's another problem with NFS && backing devices. NFS may call
> > bdi_destroy() on a bdi without ever called bdi_init(). This was always a
> > bad idea, now it's an issue.
> > 
> > So, Trond, can I safely add a server->flags private flag to indicate
> > that we have called bdi_init()? Then nfs_free_server() knows when to
> > call bdi_destroy(). Seems like the safest fix, since error handling is
> > currently 'just call nfs_free_server()'.
> 
> For the record, this makes my NULL pointer deref go away.. :-)

Good, now I just need Trond to either barf (and suggest an alternative),
or sign-off on the patch...

-- 
Jens Axboe

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