49 lines
2.0 KiB
Diff
49 lines
2.0 KiB
Diff
From aa49a6d46edfaeb414fcd70d3138ee8b28ffb343 Mon Sep 17 00:00:00 2001
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From: Ilya Maximets <i.maximets@ovn.org>
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Date: Thu, 24 Oct 2019 15:15:07 +0200
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Subject: dpif-netdev: Fix time delta overflow in case of race for meter lock.
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There is a race window between getting the time and getting the meter
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lock. This could lead to situation where the thread with larger
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current time (this thread called time_{um}sec() later than others)
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will acquire meter lock first and update meter->used to the large
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value. Next threads will try to calculate time delta by subtracting
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the large meter->used from their lower time getting the negative value
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which will be converted to a big unsigned delta.
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Fix that by assuming that all these threads received packets in the
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same time in this case, i.e. dropping negative delta to 0.
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CC: Jarno Rajahalme <jarno@ovn.org>
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Fixes: 4b27db644a8c ("dpif-netdev: Simple DROP meter implementation.")
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Reported-at: https://mail.openvswitch.org/pipermail/ovs-dev/2019-September/363126.html
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Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
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Acked-by: William Tu <u9012063@gmail.com>
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---
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lib/dpif-netdev.c | 8 ++++++++
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1 file changed, 8 insertions(+)
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diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
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index f71deb718..370840fa0 100644
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--- a/lib/dpif-netdev.c
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+++ b/lib/dpif-netdev.c
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@@ -5630,6 +5630,14 @@ dp_netdev_run_meter(struct dp_netdev *dp, struct dp_packet_batch *packets_,
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/* All packets will hit the meter at the same time. */
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long_delta_t = now / 1000 - meter->used / 1000; /* msec */
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+ if (long_delta_t < 0) {
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+ /* This condition means that we have several threads fighting for a
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+ meter lock, and the one who received the packets a bit later wins.
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+ Assuming that all racing threads received packets at the same time
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+ to avoid overflow. */
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+ long_delta_t = 0;
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+ }
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+
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/* Make sure delta_t will not be too large, so that bucket will not
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* wrap around below. */
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delta_t = (long_delta_t > (long long int)meter->max_delta_t)
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--
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2.14.1
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