linux-kernel - Re: [PATCH 2/6] xen-blkfront: handle backend CLOSED without CLOSING

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Message-ID: <506F0370.6050905@citrix.com>
Date:	Fri, 5 Oct 2012 16:57:36 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Jan Beulich <JBeulich@...e.com>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/6] xen-blkfront: handle backend CLOSED without CLOSING

On 05/10/12 12:55, Jan Beulich wrote:
>>>> On 05.10.12 at 13:42, David Vrabel <david.vrabel@...rix.com> wrote:
>> On 02/10/12 21:02, Konrad Rzeszutek Wilk wrote:
>>> On Mon, Oct 01, 2012 at 06:19:19PM +0100, David Vrabel wrote:
>>>> On 25/09/12 18:53, David Vrabel wrote:
>>>>> On 21/09/12 17:04, David Vrabel wrote:
>>>>>> From: David Vrabel <david.vrabel@...rix.com>
>>>>>>
>>>>>> Backend drivers shouldn't transistion to CLOSED unless the frontend is
>>>>>> CLOSED.  If a backend does transition to CLOSED too soon then the
>>>>>> frontend may not see the CLOSING state and will not properly shutdown.
>>>>>>
>>>>>> So, treat an unexpected backend CLOSED state the same as CLOSING.
>>>>>
>>>>> Didn't handle the frontend block device being mounted. Updated patch here.
>>>>
>>>> Konrad, can you ack this updated patch if you're happy with it.
>>>
>>> Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
>>>
>>> Or should I just carry it in my for-jens-3.7 bug-fixes queue and ask
>>> Jen to pull it once rc0 is out?
>>
>> This seems easiest, if Jan is happy with the patch.
> 
> I see the point of your explanation yesterday, but am still not
> convinced that the early cleanup in spite of active users of the
> disk can't cause any problems (like dangling pointers or NULL
> dereferences).

I tested it some more and it is broken.  Please apply the first version
instead.

blkfront needs to cancel and complete with an error requests that are
are still on the ring after the backend has disconnected and it needs to
complete with an error all requests submitted while disconnected.
Otherwise, if there is outstanding requests or new requests then
del_gendisk() blocks waiting for the I/O to complete.

David
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