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openvswitch: meter: fix race when getting now_ms.

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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.maximets@ovn.org/

Fixes: 96fbc13d7e ("openvswitch: Add meter infrastructure")
Signed-off-by: Tao Liu <thomas.liu@ucloud.cn>
Suggested-by: Ilya Maximets <i.maximets@ovn.org>
Reviewed-by: Ilya Maximets <i.maximets@ovn.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Tao Liu 2021-05-13 21:08:00 +08:00 committed by David S. Miller
parent c7d8302478
commit e4df1b0c24
1 changed files with 8 additions and 0 deletions
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8
net/openvswitch/meter.c
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@ -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.