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

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Date: Mon, 25 Mar 2024 14:29:24 +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 Mon, Mar 25, 2024 at 10:11 AM Heng Qi <hengqi@...ux.alibaba.com> wrote:
>
>
>
> 在 2024/3/22 下午1:17, Jason Wang 写道:
> > 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.
>
> The work in net_dim() core layer uses non-delayed-work, and the two
> cannot be mixed.

Well, I think we need first to figure out if delayed work is better here.

Switching to use delayed work for dim seems not hard anyhow.

Thanks

>
> Thanks,
> Heng
>
> >
> > 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
> >>
>