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SubjectRe: [PATCH 1/1] net/hyperv: Fix the code handling tx busy
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On Mon, 2012-03-19 at 10:02 -0700, Haiyang Zhang wrote:
> Instead of dropping the packet, we keep the skb buffer, and return
> NETDEV_TX_BUSY to let upper layer retry send. This will not cause
> endless loop, because the host is taking data away from ring buffer.
>
> Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
> Reviewed-by: K. Y. Srinivasan <kys@microsoft.com>
> ---
> drivers/net/hyperv/netvsc_drv.c | 5 +----
> 1 files changed, 1 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
> index 2517d20..dd29478 100644
> --- a/drivers/net/hyperv/netvsc_drv.c
> +++ b/drivers/net/hyperv/netvsc_drv.c
> @@ -223,13 +223,10 @@ static int netvsc_start_xmit(struct sk_buff *skb, struct net_device *net)
> net->stats.tx_bytes += skb->len;
> net->stats.tx_packets++;
> } else {
> - /* we are shutting down or bus overloaded, just drop packet */
> - net->stats.tx_dropped++;
> kfree(packet);
> - dev_kfree_skb_any(skb);
> }
>
> - return NETDEV_TX_OK;
> + return ret ? NETDEV_TX_BUSY : NETDEV_TX_OK;
> }
>
> /*

Thats simply not true at all.

A start_xmit() cannot do that.

TX_BUSY should never be returned at all, its a deprecated code, for
pretty good reasons. (assuming queue is not stopped)

Try this on a machine with one CPU, I am pretty sure this can trigger
complete freezes.

Once softirq loops in your start_xmit(), how do you think one process
can help you now ?





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