-----Original Message-----
From: Jakub Kicinski <kuba@kernel.org>
Sent: Monday, July 14, 2025 9:29 PM
To: Haiyang Zhang <redacted>
Cc: linux-hyperv@vger.kernel.org; netdev@vger.kernel.org; Haiyang Zhang
[off-list ref]; KY Srinivasan [off-list ref];
wei.liu@kernel.org; Dexuan Cui [off-list ref]; edumazet@google.com;
pabeni@redhat.com; stephen@networkplumber.org; davem@davemloft.net; linux-
kernel@vger.kernel.org; stable@vger.kernel.org
Subject: [EXTERNAL] Re: [PATCH net] hv_netvsc: Switch VF namespace in
netvsc_open instead

On Fri, 11 Jul 2025 13:57:10 -0700 Haiyang Zhang wrote:

quoted

The existing code move the VF NIC to new namespace when NETDEV_REGISTER

is

quoted

received on netvsc NIC. During deletion of the namespace,
default_device_exit_batch() >> default_device_exit_net() is called. When
netvsc NIC is moved back and registered to the default namespace, it
automatically brings VF NIC back to the default namespace. This will

cause

quoted

the default_device_exit_net() >> for_each_netdev_safe loop unable to

detect

quoted

the list end, and hit NULL ptr:

Are you saying that when netns is dismantled both devices are listed
for moving back to default, but the netvsc_event_set_vf_ns() logic
tries to undo the move / move the VF before the netns dismantle loop
got to it?

netvsc_event_set_vf_ns() moves the VF to default ns before the netns 
dismantle loop got to it, and causes the Null prt error.

This needs a better fix, moving on open is way too hacky.
Perhaps we should start with reverting 4c262801ea60 and then trying
to implement it in a more robust way?

This patch reverts the 4c262801ea60, and moves the logic to netvsc_open().

I was thinking some other ways too... But seems I couldn't find a way
to know it's in the for_each_netdev_safe loop, and to skip moving the 
VF in netvsc_event_set_vf_ns() this case.

Thanks,
- Haiyang