On 5/13/21 3:08 PM, Tao Liu wrote:
> We have observed meters working unexpected if traffic is 3+Gbit/s
> with multiple connections.
>
> now_ms is not pretected by meter->lock, we may get a negative
> long_delta_ms when another cpu updated meter->used, then:
> delta_ms = (u32)long_delta_ms;
> which will be a large value.
>
> band->bucket += delta_ms * band->rate;
> then we get a wrong band->bucket.
>
> OpenVswitch userspace datapath has fixed the same issue[1] some
> time ago, and we port the implementation to kernel datapath.
>
> [1]
> https://patchwork.ozlabs.org/project/openvswitch/patch/20191025114436.9746-1-i.maxim...@ovn.org/
>
> Fixes: 96fbc13d7e77 ("openvswitch: Add meter infrastructure")
> Signed-off-by: Tao Liu <thomas....@ucloud.cn>
> Suggested-by: Ilya Maximets <i.maxim...@ovn.org>
> ---
> Changelog:
> v2: just set negative long_delta_ms to zero in case of race for meter lock.
> v1: make now_ms protected by meter lock.
> ---
Thanks!
I didn't test it, but the change looks good to me.
Reviewed-by: Ilya Maximets <i.maxim...@ovn.org>
> net/openvswitch/meter.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/net/openvswitch/meter.c b/net/openvswitch/meter.c
> index 96b524c..896b8f5 100644
> --- a/net/openvswitch/meter.c
> +++ b/net/openvswitch/meter.c
> @@ -611,6 +611,14 @@ bool ovs_meter_execute(struct datapath *dp, struct
> sk_buff *skb,
> spin_lock(&meter->lock);
>
> long_delta_ms = (now_ms - meter->used); /* ms */
> + if (long_delta_ms < 0) {
> + /* This condition means that we have several threads fighting
> + * for a meter lock, and the one who received the packets a
> + * bit later wins. Assuming that all racing threads received
> + * packets at the same time to avoid overflow.
> + */
> + long_delta_ms = 0;
> + }
>
> /* Make sure delta_ms will not be too large, so that bucket will not
> * wrap around below.
>
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