netdev - Re: [PATCH 1/2] virtio-net: fix possible dim status unrecoverable

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Date: Fri, 22 Mar 2024 13:17:14 +0800
From: Jason Wang <jasowang@...hat.com>
To: Heng Qi <hengqi@...ux.alibaba.com>
Cc: netdev@...r.kernel.org, virtualization@...ts.linux.dev, 
	"Michael S. Tsirkin" <mst@...hat.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Eric Dumazet <edumazet@...gle.com>, "David S. Miller" <davem@...emloft.net>, 
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Subject: Re: [PATCH 1/2] virtio-net: fix possible dim status unrecoverable

On Thu, Mar 21, 2024 at 7:46 PM Heng Qi <hengqi@...ux.alibaba.com> wrote:
>
> When the dim worker is scheduled, if it fails to acquire the lock,
> dim may not be able to return to the working state later.
>
> For example, the following single queue scenario:
>   1. The dim worker of rxq0 is scheduled, and the dim status is
>      changed to DIM_APPLY_NEW_PROFILE;
>   2. The ethtool command is holding rtnl lock;
>   3. Since the rtnl lock is already held, virtnet_rx_dim_work fails
>      to acquire the lock and exits;
>
> Then, even if net_dim is invoked again, it cannot work because the
> state is not restored to DIM_START_MEASURE.
>
> Fixes: 6208799553a8 ("virtio-net: support rx netdim")
> Signed-off-by: Heng Qi <hengqi@...ux.alibaba.com>
> ---
>  drivers/net/virtio_net.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index c22d111..0ebe322 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -3563,8 +3563,10 @@ static void virtnet_rx_dim_work(struct work_struct *work)
>         struct dim_cq_moder update_moder;
>         int i, qnum, err;
>
> -       if (!rtnl_trylock())
> +       if (!rtnl_trylock()) {
> +               schedule_work(&dim->work);
>                 return;
> +       }

Patch looks fine but I wonder if a delayed schedule is better.

Thanks

>
>         /* Each rxq's work is queued by "net_dim()->schedule_work()"
>          * in response to NAPI traffic changes. Note that dim->profile_ix
> --
> 1.8.3.1
>