Re: [PATCH v4] virtio_net: suppress cpu stall when free_unused_bufs

From: "Michael S. Tsirkin" <mst@redhat.com>
To: Wenliang Wang <wangwenliang.1995@bytedance.com>
Cc: xuanzhuo@linux.alibaba.com, willemdebruijn.kernel@gmail.com,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	zhengqi.arch@bytedance.com,
	virtualization@lists.linux-foundation.org, edumazet@google.com,
	kuba@kernel.org, pabeni@redhat.com, davem@davemloft.net
Subject: Re: [PATCH v4] virtio_net: suppress cpu stall when free_unused_bufs
Date: Thu, 4 May 2023 03:06:10 -0400	[thread overview]
Message-ID: <20230504030546-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <1683167226-7012-1-git-send-email-wangwenliang.1995@bytedance.com>

On Thu, May 04, 2023 at 10:27:06AM +0800, Wenliang Wang 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@bytedance.com>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

Probably a good idea for stable, too.

> ---
> 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();
>  	}
>  
>  	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

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