On 4/8/25 14:34, Jason Wang wrote:
On Mon, Apr 7, 2025 at 10:27 AM Bui Quang Minh <minhquangbui99@xxxxxxxxx> wrote:
On 4/7/25 08:03, Xuan Zhuo wrote:
On Fri, 4 Apr 2025 16:39:03 +0700, Bui Quang Minh <minhquangbui99@xxxxxxxxx> 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 <kuba@xxxxxxxxxx>
Date: Tue Jan 14 19:53:14 2025 -0800
net: protect NAPI enablement with netdev_lock()
?
I'm not aware of this, will update the fix tags in the next patch.
I wonder if it's simpler to just hold the netdev lock in resize or xsk
binding instead of this.
That looks cleaner, let me try that approach.
Thanks,
Quang Minh
