Re: [Xen-devel] [PATCH 2/2] xen-netfront: Fix race between device setup and open

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

On 01/11/2018 03:26 PM, David Miller wrote:
> From: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
> Date: Thu, 11 Jan 2018 09:36:38 +0000
>
> > When a netfront device is set up it registers a netdev fairly early on,
> > before it has set up the queues and is actually usable. A userspace tool
> > like NetworkManager will immediately try to open it and access its state
> > as soon as it appears. The bug can be reproduced by hotplugging VIFs
> > until the VM runs out of grant refs. It registers the netdev but fails
> > to set up any queues (since there are no more grant refs). In the
> > meantime, NetworkManager opens the device and the kernel crashes trying
> > to access the queues (of which there are none).
> >
> > Fix this in two ways:
> > * For initial setup, register the netdev much later, after the queues
> > are setup. This avoids the race entirely.
> > * During a suspend/resume cycle, the frontend reconnects to the backend
> > and the queues are recreated. It is possible (though highly unlikely) to
> > race with something opening the device and accessing the queues after
> > they have been destroyed but before they have been recreated. Extend the
> > region covered by the rtnl semaphore to protect against this race. There
> > is a possibility that we fail to recreate the queues so check for this
> > in the open function.
> >
> > Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
> Where is patch 1/2 and the 0/2 header posting which explains what this
> patch series is doing, how it is doing it, and why it is doing it that
> way?
I've now added CC'd netdev on the other two.

Cheers,
--
Ross Lagerwall

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