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

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Date:   Thu, 3 Jun 2021 18:04:31 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     Leonid Bloch <leonidb@...cscloud.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Long Li <longli@...rosoft.com>
CC:     "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [BUG] hv_netvsc: Unbind exits before the VFs bound to it are
 unregistered

> From: Leonid Bloch <leonidb@...cscloud.com>
> Sent: Thursday, June 3, 2021 5:35 AM
> To: KY Srinivasan <kys@...rosoft.com>; Haiyang Zhang
> <haiyangz@...rosoft.com>; Stephen Hemminger
> <sthemmin@...rosoft.com>; Wei Liu <wei.liu@...nel.org>; Dexuan Cui
> <decui@...rosoft.com>
> Cc: linux-hyperv@...r.kernel.org; netdev@...r.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