tcp_bbr: remove sk_pacing_rate=0 transient during init

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
rate.

Fixes: 0f8782ea1497 ("tcp_bbr: add BBR congestion control")
Reported-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c
index 3276140c25067c7fe56ed742aa807087b5bfa35d..42e0017f2ebccefb53506676df6bfab7c1dbc536 100644 (file)
--- a/net/ipv4/tcp_bbr.c
+++ b/net/ipv4/tcp_bbr.c
@@ -837,7 +837,6 @@ 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_init_pacing_rate_from_rtt(sk);
 
        bbr->restore_cwnd = 0;