[SRU][Zesty][PATCH 4/5] tcp_bbr: remove sk_pacing_rate=0 transient during init

Vinson Lee vlee at freedesktop.org
Tue Sep 12 23:12:16 UTC 2017

From: Neal Cardwell <ncardwell at google.com>

BugLink: https://bugs.launchpad.net/bugs/1708604

Fix a corner case noticed by Eric Dumazet, where BBR's setting
sk->sk_pacing_rate to 0 during initialization could theoretically
cause packets in the sending host to hang if there were packets "in
flight" in the pacing infrastructure at the time the BBR congestion
control state is initialized. This could occur if the pacing
infrastructure happened to race with bbr_init() in a way such that the
pacer read the 0 rather than the immediately following non-zero pacing

Fixes: 0f8782ea1497 ("tcp_bbr: add BBR congestion control")
Reported-by: Eric Dumazet <edumazet at google.com>
Signed-off-by: Neal Cardwell <ncardwell at google.com>
Signed-off-by: Yuchung Cheng <ycheng at google.com>
Signed-off-by: Soheil Hassas Yeganeh <soheil at google.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
(cherry picked from commit 1d3648eb5d1fe9ed3d095ed8fa19ad11ca4c8bc0)
Signed-off-by: Vinson Lee <vlee at freedesktop.org>
 net/ipv4/tcp_bbr.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c
index e69c8b44568a..20d834fd557d 100644
--- a/net/ipv4/tcp_bbr.c
+++ b/net/ipv4/tcp_bbr.c
@@ -838,7 +838,6 @@ static void bbr_init(struct sock *sk)
 	minmax_reset(&bbr->bw, bbr->rtt_cnt, 0);  /* init max bw to 0 */
-	sk->sk_pacing_rate = 0;		/* force an update of sk_pacing_rate */
 	bbr->restore_cwnd = 0;

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