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.
---
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.
--
1.8.3.1
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