On Tue, Apr 29, 2025 at 10:31 PM Jakub Kicinski <k...@kernel.org> wrote:
>
> Commit 4bc12818b363 ("virtio-net: disable delayed refill when pausing rx")
> fixed a deadlock between reconfig paths and refill work trying to disable
> the same NAPI instance. The refill work can't run in parallel with reconfig
> because trying to double-disable a NAPI instance causes a stall under the
> instance lock, which the reconfig path needs to re-enable the NAPI and
> therefore unblock the stalled thread.
>
> There are two cases where we re-enable refill too early. One is in the
> virtnet_set_queues() handler. We call it when installing XDP:
>
> virtnet_rx_pause_all(vi);
> ...
> virtnet_napi_tx_disable(..);
> ...
> virtnet_set_queues(..);
> ...
> virtnet_rx_resume_all(..);
>
> We want the work to be disabled until we call virtnet_rx_resume_all(),
> but virtnet_set_queues() kicks it before NAPIs were re-enabled.
>
> The other case is a more trivial case of mis-ordering in
> __virtnet_rx_resume() found by code inspection.
>
> Fixes: 4bc12818b363 ("virtio-net: disable delayed refill when pausing rx")
> Fixes: 413f0271f396 ("net: protect NAPI enablement with netdev_lock()")
> Signed-off-by: Jakub Kicinski <k...@kernel.org>
> ---
> CC: m...@redhat.com
> CC: jasow...@redhat.com
> CC: xuanz...@linux.alibaba.com
> CC: epere...@redhat.com
> CC: minhquangbu...@gmail.com
> CC: rom...@fr.zoreil.com
> CC: kun...@amazon.com
> CC: virtualizat...@lists.linux.dev
> ---
> drivers/net/virtio_net.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 848fab51dfa1..4c904e176495 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -3383,12 +3383,15 @@ static void __virtnet_rx_resume(struct virtnet_info
> *vi,
> bool refill)
> {
> bool running = netif_running(vi->dev);
> + bool schedule_refill = false;
>
> if (refill && !try_fill_recv(vi, rq, GFP_KERNEL))
> - schedule_delayed_work(&vi->refill, 0);
> -
> + schedule_refill = true;
> if (running)
> virtnet_napi_enable(rq);
> +
> + if (schedule_refill)
> + schedule_delayed_work(&vi->refill, 0);
> }
>
> static void virtnet_rx_resume_all(struct virtnet_info *vi)
> @@ -3728,7 +3731,7 @@ static int virtnet_set_queues(struct virtnet_info *vi,
> u16 queue_pairs)
> succ:
> vi->curr_queue_pairs = queue_pairs;
> /* virtnet_open() will refill when device is going to up. */
> - if (dev->flags & IFF_UP)
> + if (dev->flags & IFF_UP && vi->refill_enabled)
> schedule_delayed_work(&vi->refill, 0);
This has the assumption that the toggle of the refill_enabled is under
RTNL. Though it's true now but it looks to me it's better to protect
it against refill_lock.
Thanks
>
> return 0;
> --
> 2.49.0
>
