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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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