From d8069dc878b3222d2bb37765a2567e367630a003 Mon Sep 17 00:00:00 2001 From: Ilya Maximets Date: Thu, 24 Oct 2019 15:15:07 +0200 Subject: [PATCH] dpif-netdev: Fix time delta overflow in case of race for meter lock. There is a race window between getting the time and getting the meter lock. This could lead to situation where the thread with larger current time (this thread called time_{um}sec() later than others) will acquire meter lock first and update meter->used to the large value. Next threads will try to calculate time delta by subtracting the large meter->used from their lower time getting the negative value which will be converted to a big unsigned delta. Fix that by assuming that all these threads received packets in the same time in this case, i.e. dropping negative delta to 0. CC: Jarno Rajahalme Fixes: 4b27db644a8c ("dpif-netdev: Simple DROP meter implementation.") Reported-at: https://mail.openvswitch.org/pipermail/ovs-dev/2019-September/363126.html Signed-off-by: Ilya Maximets Acked-by: William Tu --- lib/dpif-netdev.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c index 7bc47f265d6..55aec8ab8f8 100644 --- a/lib/dpif-netdev.c +++ b/lib/dpif-netdev.c @@ -5066,6 +5066,14 @@ dp_netdev_run_meter(struct dp_netdev *dp, struct dp_packet_batch *packets_, /* All packets will hit the meter at the same time. */ long_delta_t = now / 1000 - meter->used / 1000; /* msec */ + if (long_delta_t < 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_t = 0; + } + /* Make sure delta_t will not be too large, so that bucket will not * wrap around below. */ delta_t = (long_delta_t > (long long int)meter->max_delta_t)