On Wed, 6 Sep 2017 16:23:45 +
Haiyang Zhang wrote:
> > -Original Message-
> > From: Stephen Hemminger [mailto:step...@networkplumber.org]
> > Sent: Wednesday, September 6, 2017 11:19 AM
> > To: KY Srinivasan ; Haiyang Zhang
> > ; Stephen Hemminger
> > Cc: de...@linuxdriverproject.org; netdev@vger.kernel.org
> > Subject: [PATCH net-next 1/1] hv_netvsc: fix deadlock on hotplug
> >
> > When a virtual device is added dynamically (via host console), then
> > the vmbus sends an offer message for the primary channel. The processing
> > of this message for networking causes the network device to then
> > initialize the sub channels.
> >
> > The problem is that setting up the sub channels needs to wait until
> > the subsequent subchannel offers have been processed. These offers
> > come in on the same ring buffer and work queue as where the primary
> > offer is being processed; leading to a deadlock.
> >
> > This did not happen in older kernels, because the sub channel waiting
> > logic was broken (it wasn't really waiting).
> >
> > The solution is to do the sub channel setup in its own work queue
> > context that is scheduled by the primary channel setup; and then
> > happens later.
> >
> > Fixes: 732e49850c5e ("netvsc: fix race on sub channel creation")
> > Reported-by: Dexuan Cui
> > Signed-off-by: Stephen Hemminger
> > ---
> > Should also go to stable, but this version does not apply cleanly
> > to 4.13. Have another patch for that.
> >
> > drivers/net/hyperv/hyperv_net.h | 1 +
> > drivers/net/hyperv/netvsc_drv.c | 8 +--
> > drivers/net/hyperv/rndis_filter.c | 106 ++-
> > ---
> > 3 files changed, 74 insertions(+), 41 deletions(-)
>
> The patch looks overall. I just have a question:
>
> With this patch, after module load and probe is done, there may still be
> subchannels being processed. If rmmod immediately, the subchannel offers
> may hit half-way removed device structures... Do we also need to add
> cancel_work_sync(&dev->subchan_work) to the top of netvsc_remove()?
>
> unregister_netdevice() includes device close, but it's only called later
> in the netvsc_remove() when rndis is already removed.
>
> Thanks,
> - Haiyang
Good catch.
If the driver called unregister_netdevice first before doing
rndis_filter_device_remove
that would solve the problem. That wouldn't cause additional problems and it
makes
sense to close the network layer first.
