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Subject[PATCH 4/4] virtio-net: sleep instead of busy waiting for cvq command
Date
We used to busy waiting on the cvq command this tends to be
problematic since:

1) CPU could wait for ever on a buggy/malicous device
2) There's no wait to terminate the process that triggers the cvq
command

So this patch switch to use virtqueue_wait_for_used() to sleep with a
timeout (1s) instead of busy polling for the cvq command forever. This
gives the scheduler a breath and can let the process can respond to
asignal. If the device doesn't respond in the timeout, break the
device.

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
Changes since V1:
- break the device when timeout
- get buffer manually since the virtio core check more_used() instead
---
drivers/net/virtio_net.c | 24 ++++++++++++++++--------
1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index efd9dd55828b..6a2ea64cfcb5 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -405,6 +405,7 @@ static void disable_rx_mode_work(struct virtnet_info *vi)
vi->rx_mode_work_enabled = false;
spin_unlock_bh(&vi->rx_mode_lock);

+ virtqueue_wake_up(vi->cvq);
flush_work(&vi->rx_mode_work);
}

@@ -1497,6 +1498,11 @@ static bool try_fill_recv(struct virtnet_info *vi, struct receive_queue *rq,
return !oom;
}

+static void virtnet_cvq_done(struct virtqueue *cvq)
+{
+ virtqueue_wake_up(cvq);
+}
+
static void skb_recv_done(struct virtqueue *rvq)
{
struct virtnet_info *vi = rvq->vdev->priv;
@@ -1984,6 +1990,8 @@ static int virtnet_tx_resize(struct virtnet_info *vi,
return err;
}

+static int virtnet_close(struct net_device *dev);
+
/*
* Send command via the control virtqueue and check status. Commands
* supported by the hypervisor, as indicated by feature bits, should
@@ -2026,14 +2034,14 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
if (unlikely(!virtqueue_kick(vi->cvq)))
return vi->ctrl->status == VIRTIO_NET_OK;

- /* Spin for a response, the kick causes an ioport write, trapping
- * into the hypervisor, so the request should be handled immediately.
- */
- while (!virtqueue_get_buf(vi->cvq, &tmp) &&
- !virtqueue_is_broken(vi->cvq))
- cpu_relax();
+ if (virtqueue_wait_for_used(vi->cvq)) {
+ virtqueue_get_buf(vi->cvq, &tmp);
+ return vi->ctrl->status == VIRTIO_NET_OK;
+ }

- return vi->ctrl->status == VIRTIO_NET_OK;
+ netdev_err(vi->dev, "CVQ command timeout, break the virtio device.");
+ virtio_break_device(vi->vdev);
+ return VIRTIO_NET_ERR;
}

static int virtnet_set_mac_address(struct net_device *dev, void *p)
@@ -3526,7 +3534,7 @@ static int virtnet_find_vqs(struct virtnet_info *vi)

/* Parameters for control virtqueue, if any */
if (vi->has_cvq) {
- callbacks[total_vqs - 1] = NULL;
+ callbacks[total_vqs - 1] = virtnet_cvq_done;
names[total_vqs - 1] = "control";
}

--
2.25.1
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