Subject: Re: [PATCH] nfs: fix bdi_unregister() before sb kill
From: Trond Myklebust <trond.myklebust@fys.uio.no>
To: Jens Axboe <jens.axboe@oracle.com>
Cc: Linux Kernel <linux-kernel@vger.kernel.org>, a.p.zijlstra@chello.nl
In-Reply-To: <20090917194027.GS23126@kernel.dk>
References: <20090917124233.GJ23126@kernel.dk>
	 <20090917194027.GS23126@kernel.dk>
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Date: Thu, 17 Sep 2009 19:16:50 -0400
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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()'.

Urgh... Is there any reason why we can't just move the call to
bdi_init() into nfs_bdi_register()? It seems bizarre to have to
initialise the backing_dev_info twice like this...

If we do that, then we can just look at the BDI_registered state flag in
order to figure out if we need to call bdi_unregister()

Cheers
  Trond

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