linux-kernel - Re: [PATCH v4] virtio_net: suppress cpu stall when free_unused

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Date:   Fri, 5 May 2023 11:28:25 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Wenliang Wang <wangwenliang.1995@...edance.com>
Cc:     mst@...hat.com, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com, zhengqi.arch@...edance.com,
        willemdebruijn.kernel@...il.com,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, xuanzhuo@...ux.alibaba.com
Subject: Re: [PATCH v4] virtio_net: suppress cpu stall when free_unused_bufs

On Thu, May 4, 2023 at 10:27 AM Wenliang Wang
<wangwenliang.1995@...edance.com> wrote:
>
> For multi-queue and large ring-size use case, the following error
> occurred when free_unused_bufs:
> rcu: INFO: rcu_sched self-detected stall on CPU.
>
> Fixes: 986a4f4d452d ("virtio_net: multiqueue support")
> Signed-off-by: Wenliang Wang <wangwenliang.1995@...edance.com>
> ---
> v2:
> -add need_resched check.
> -apply same logic to sq.
> v3:
> -use cond_resched instead.
> v4:
> -add fixes tag
> ---
>  drivers/net/virtio_net.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 8d8038538fc4..a12ae26db0e2 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -3560,12 +3560,14 @@ static void free_unused_bufs(struct virtnet_info *vi)
>                 struct virtqueue *vq = vi->sq[i].vq;
>                 while ((buf = virtqueue_detach_unused_buf(vq)) != NULL)
>                         virtnet_sq_free_unused_buf(vq, buf);
> +               cond_resched();

Does this really address the case when the virtqueue is very large?

Thanks

>         }
>
>         for (i = 0; i < vi->max_queue_pairs; i++) {
>                 struct virtqueue *vq = vi->rq[i].vq;
>                 while ((buf = virtqueue_detach_unused_buf(vq)) != NULL)
>                         virtnet_rq_free_unused_buf(vq, buf);
> +               cond_resched();
>         }
>  }
>
> --
> 2.20.1
>