RE: [BUG] hv_netvsc: Unbind exits before the VFs bound to it are unregistered

[Dexuan Cui <decui@microsoft.com>]

> From: Leonid Bloch <leonidb@asocscloud.com>
> Sent: Friday, June 4, 2021 1:14 AM
> To: Dexuan Cui <decui@microsoft.com>; KY Srinivasan <kys@microsoft.com>;
> Haiyang Zhang <haiyangz@microsoft.com>; Stephen Hemminger
> <sthemmin@microsoft.com>; Wei Liu <wei.liu@kernel.org>; Long Li
> <longli@microsoft.com>
> Cc: linux-hyperv@vger.kernel.org; netdev@vger.kernel.org
> Subject: Re: [BUG] hv_netvsc: Unbind exits before the VFs bound to it are
> unregistered
> 
> On 6/3/21 9:04 PM, Dexuan Cui wrote:
> >> From: Leonid Bloch <leonidb@asocscloud.com>
> >> Sent: Thursday, June 3, 2021 5:35 AM
> >> To: KY Srinivasan <kys@microsoft.com>; Haiyang Zhang
> >> <haiyangz@microsoft.com>; Stephen Hemminger
> >> <sthemmin@microsoft.com>; Wei Liu <wei.liu@kernel.org>; Dexuan Cui
> >> <decui@microsoft.com>
> >> Cc: linux-hyperv@vger.kernel.org; netdev@vger.kernel.org
> >> Subject: [BUG] hv_netvsc: Unbind exits before the VFs bound to it are
> >> unregistered
> >>
> >> Hi,
> >>
> >> When I try to unbind a network interface from hv_netvsc and bind it to
> >> uio_hv_generic, once in a while I get the following kernel panic (please
> >> note the first two lines: it seems as uio_hv_generic is registered
> >> before the VF bound to hv_netvsc is unregistered):
> >>
> >> [Jun 3 09:04] hv_vmbus: registering driver uio_hv_generic
> >> [  +0.002215] hv_netvsc 5e089342-8a78-4b76-9729-25c81bd338fc eth2:
> VF
> >> unregistering: eth5
> >> [  +1.088078] BUG: scheduling while atomic: swapper/8/0/0x00010003
> >> [  +0.000001] BUG: scheduling while atomic: swapper/3/0/0x00010003
> >> [  +0.000001] BUG: scheduling while atomic: swapper/6/0/0x00010003
> >> [  +0.000000] BUG: scheduling while atomic: swapper/7/0/0x00010003
> >> [  +0.000005] Modules linked in:
> >> [  +0.000001] Modules linked in:
> >> [  +0.000001]  uio_hv_generic
> >> [  +0.000000] Modules linked in:
> >> [  +0.000000] Modules linked in:
> >> [  +0.000001]  uio_hv_generic uio
> >> [  +0.000001]  uio
> >> [  +0.000000]  uio_hv_generic
> >> [  +0.000000]  uio_hv_generic
> >> ...
> >>
> >> I run kernel 5.10.27, unmodified, besides RT patch v36, on Azure Stack
> >> Edge platform, software version 2105 (2.2.1606.3320).
> >>
> >> I perform the bind-unbind using the following script (please note the
> >> comment inline):
> >>
> >> net_uuid="f8615163-df3e-46c5-913f-f2d2f965ed0e"
> >> dev_uuid="$(basename "$(readlink "/sys/class/net/eth1/device")")"
> >> modprobe uio_hv_generic
> >> echo "${net_uuid}" > /sys/bus/vmbus/drivers/uio_hv_generic/new_id
> >> printf "%s" "${dev_uuid}" > /sys/bus/vmbus/drivers/hv_netvsc/unbind
> >> ### If I insert 'sleep 1' here - all works correctly
> >> printf "%s" "${dev_uuid}" > /sys/bus/vmbus/drivers/uio_hv_generic/bind
> >>
> >>
> >> Thanks,
> >> Leonid.
> >
> > It would be great if you can test the mainline kernel, which I suspect also
> > has the bug.
> >
> > It looks like netvsc_remove() -> netvsc_unregister_vf() does the unbinding
> work
> > in a synchronous mannter. I don't know why the bug happens.
> >
> > Right now I don't have a DPDK setup to test this, but I think the bug can
> > be worked around by unbinding the PCI VF device from the pci-hyperv driver
> > before unbinding the netvsc device, and re-binding the VF device after
> binding
> > the netvsc device to uio_hv_generic.
> >
> > Thanks,
> > -- Dexuan
> >
> 
> Hi Dexuan,
> 
> Thanks for your reply. I can check for myself only next week, as I am
> out of office now, but do you think that the reason might be using
> cancel_delayed_work_sync(), instead of cancel_delayed_work() in
> netvsc_unregister_vf()?

I'm not sure. I don't understand how the error happens:
[  +1.088078] BUG: scheduling while atomic: swapper/8/0/0x00010003
 
> And if the above is not correct, can you please advise on a way of
> finding the corresponding VF device from userspace, given the kernel
> name of the parent device? I did not find it in sysfs so far.
> 
> Thanks,
> Leonid.

The VF NIC interface's MAC address is the same as the that of the matching 
netvsc NIC. We should be able to find the <netvsc NIC, VF NIC> pair by
checking /sys/class/net/*/address.