On 4/8/25 9:34 AM, Jason Wang wrote:
> On Mon, Apr 7, 2025 at 10:27 AM Bui Quang Minh <minhquangbu...@gmail.com>
> wrote:
>> On 4/7/25 08:03, Xuan Zhuo wrote:
>>> On Fri, 4 Apr 2025 16:39:03 +0700, Bui Quang Minh
>>> <minhquangbu...@gmail.com> wrote:
>>>> When pausing rx (e.g. set up xdp, xsk pool, rx resize), we call
>>>> napi_disable() on the receive queue's napi. In delayed refill_work, it
>>>> also calls napi_disable() on the receive queue's napi. This can leads to
>>>> deadlock when napi_disable() is called on an already disabled napi. This
>>>> scenario can be reproducible by binding a XDP socket to virtio-net
>>>> interface without setting up the fill ring. As a result, try_fill_recv
>>>> will fail until the fill ring is set up and refill_work is scheduled.
>>>
>>> So, what is the problem? The refill_work is waiting? As I know, that thread
>>> will sleep some time, so the cpu can do other work.
>>
>> When napi_disable is called on an already disabled napi, it will sleep
>> in napi_disable_locked while still holding the netdev_lock. As a result,
>> later napi_enable gets stuck too as it cannot acquire the netdev_lock.
>> This leads to refill_work and the pause-then-resume tx are stuck altogether.
>
> This needs to be added to the chagelog. And it looks like this is a fix for
>
> commit 413f0271f3966e0c73d4937963f19335af19e628
> Author: Jakub Kicinski <k...@kernel.org>
> Date: Tue Jan 14 19:53:14 2025 -0800
>
> net: protect NAPI enablement with netdev_lock()
>
> ?
>
> I wonder if it's simpler to just hold the netdev lock in resize or xsk
> binding instead of this.
Setting:
dev->request_ops_lock = true;
in virtnet_probe() before calling register_netdevice() should achieve
the above. Could you please have a try?
Thanks,
Paolo
