netdev - Re: [Xen-devel] [PATCH] xen-netfront: Fix hang on device removal

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Date:   Fri, 20 Apr 2018 08:41:25 -0400
From:   Jason Andryuk <jandryuk@...il.com>
To:     Simon Gaiser <simon@...isiblethingslab.com>
Cc:     netdev@...r.kernel.org, xen-devel@...ts.xenproject.org,
        Eduardo Otubo <otubo@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH] xen-netfront: Fix hang on device removal

On Thu, Apr 19, 2018 at 4:09 PM, Simon Gaiser
<simon@...isiblethingslab.com> wrote:
> Jason Andryuk:
>> On Thu, Apr 19, 2018 at 2:10 PM, Simon Gaiser
>> <simon@...isiblethingslab.com> wrote:
>>> Jason Andryuk:
>>>> A toolstack may delete the vif frontend and backend xenstore entries
>>>> while xen-netfront is in the removal code path.  In that case, the
>>>> checks for xenbus_read_driver_state would return XenbusStateUnknown, and
>>>> xennet_remove would hang indefinitely.  This hang prevents system
>>>> shutdown.
>>>>
>>>> xennet_remove must be able to handle XenbusStateUnknown, and
>>>> netback_changed must also wake up the wake_queue for that state as well.
>>>>
>>>> Fixes: 5b5971df3bc2 ("xen-netfront: remove warning when unloading module")
>>>
>>> I think this should go into stable since AFAIK the hanging network
>>> device can only be fixed by rebooting the guest. AFAICS this affects all
>>> 4.* branches since 5b5971df3bc2 got backported to them.
>>>
>>> Upstream commit c2d2e6738a209f0f9dffa2dc8e7292fc45360d61.
>>
>> Simon,
>>
>> Yes, I agree.  I actually submitted the request to stable earlier
>> today, so hopefully it gets added soon.
>
> Ok, great. (I checked the stable patch queue, but didn't check the
> mailing list archive).
>
>> Have you experienced this hang?
>
> Yes, it's affecting the kernel shipped by Qubes OS (see [1]).

Ok, interesting.  I tracked down this bug with older xenvm tools, and
I didn't know if libxl tools were also affected.

Greg KH added the patch to the stable queue, so it's in the process.

Regards,
Jason