netdev - Re: [Patch net v3] vsock/virtio: fix variables initialization during resuming

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Message-ID: <yixatl5meez3ijzumebqkhf3sywwmiicwbsuxxsfdyfeeaapw2@dq542v2lclvm>
Date: Fri, 14 Feb 2025 10:13:16 +0100
From: Luigi Leonardi <leonardi@...hat.com>
To: Junnan Wu <junnan01.wu@...sung.com>
Cc: sgarzare@...hat.com, davem@...emloft.net, edumazet@...gle.com, 
	eperezma@...hat.com, horms@...nel.org, jasowang@...hat.com, kuba@...nel.org, 
	kvm@...r.kernel.org, lei19.wang@...sung.com, linux-kernel@...r.kernel.org, 
	mst@...hat.com, netdev@...r.kernel.org, pabeni@...hat.com, q1.huang@...sung.com, 
	stefanha@...hat.com, virtualization@...ts.linux.dev, xuanzhuo@...ux.alibaba.com, 
	ying01.gao@...sung.com, ying123.xu@...sung.com
Subject: Re: [Patch net v3] vsock/virtio: fix variables initialization during
 resuming

On Fri, Feb 14, 2025 at 09:22:00AM +0800, Junnan Wu wrote:
>When executing suspend to ram twice in a row,
>the `rx_buf_nr` and `rx_buf_max_nr` increase to three times vq->num_free.
>Then after virtqueue_get_buf and `rx_buf_nr` decreased
>in function virtio_transport_rx_work,
>the condition to fill rx buffer
>(rx_buf_nr < rx_buf_max_nr / 2) will never be met.
>
>It is because that `rx_buf_nr` and `rx_buf_max_nr`
>are initialized only in virtio_vsock_probe(),
>but they should be reset whenever virtqueues are recreated,
>like after a suspend/resume.
>
>Move the `rx_buf_nr` and `rx_buf_max_nr` initialization in
>virtio_vsock_vqs_init(), so we are sure that they are properly
>initialized, every time we initialize the virtqueues, either when we
>load the driver or after a suspend/resume.
>
>To prevent erroneous atomic load operations on the `queued_replies`
>in the virtio_transport_send_pkt_work() function
>which may disrupt the scheduling of vsock->rx_work
>when transmitting reply-required socket packets,
>this atomic variable must undergo synchronized initialization
>alongside the preceding two variables after a suspend/resume.
>
>Fixes: bd50c5dc182b ("vsock/virtio: add support for device suspend/resume")
>Link: https://lore.kernel.org/virtualization/20250207052033.2222629-1-junnan01.wu@samsung.com/
>Co-developed-by: Ying Gao <ying01.gao@...sung.com>
>Signed-off-by: Ying Gao <ying01.gao@...sung.com>
>Signed-off-by: Junnan Wu <junnan01.wu@...sung.com>
>---
> net/vmw_vsock/virtio_transport.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
>diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
>index b58c3818f284..f0e48e6911fc 100644
>--- a/net/vmw_vsock/virtio_transport.c
>+++ b/net/vmw_vsock/virtio_transport.c
>@@ -670,6 +670,13 @@ static int virtio_vsock_vqs_init(struct virtio_vsock *vsock)
> 	};
> 	int ret;
>
>+	mutex_lock(&vsock->rx_lock);
>+	vsock->rx_buf_nr = 0;
>+	vsock->rx_buf_max_nr = 0;
>+	mutex_unlock(&vsock->rx_lock);
>+
>+	atomic_set(&vsock->queued_replies, 0);
>+
> 	ret = virtio_find_vqs(vdev, VSOCK_VQ_MAX, vsock->vqs, vqs_info, NULL);
> 	if (ret < 0)
> 		return ret;
>@@ -779,9 +786,6 @@ static int virtio_vsock_probe(struct virtio_device *vdev)
>
> 	vsock->vdev = vdev;
>
>-	vsock->rx_buf_nr = 0;
>-	vsock->rx_buf_max_nr = 0;
>-	atomic_set(&vsock->queued_replies, 0);
>
> 	mutex_init(&vsock->tx_lock);
> 	mutex_init(&vsock->rx_lock);
>-- 
>2.34.1
>

Reviewed-by: Luigi Leonardi <leonardi@...hat.com>