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

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Date:   Thu, 19 Apr 2018 20:09:00 +0000
From:   Simon Gaiser <simon@...isiblethingslab.com>
To:     Jason Andryuk <jandryuk@...il.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

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]).

Thanks, Simon.

[1]: https://github.com/QubesOS/qubes-issues/issues/3657



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