4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Neal Cardwell ncardwell@google.com
[ Upstream commit e6e6a278b1eaffa19d42186bfacd1ffc15a50b3f ]
Previously the bbr->idle_restart tracking was zeroing out the bbr->idle_restart bit upon ACKs that did not SACK or ACK anything, e.g. receiving incoming data or receiver window updates. In such situations BBR would forget that this was a restart-from-idle situation, and if the min_rtt had expired it would unnecessarily enter PROBE_RTT (even though we were actually restarting from idle but had merely forgotten that fact).
The fix is simple: we need to remember we are restarting from idle until we receive a S/ACK for some data (a S/ACK for the first flight of data we send as we are restarting).
This commit is a stable candidate for kernels back as far as 4.9.
Fixes: 0f8782ea1497 ("tcp_bbr: add BBR congestion control") 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: Priyaranjan Jha priyarjha@google.com Signed-off-by: Yousuk Seung ysseung@google.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv4/tcp_bbr.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
--- a/net/ipv4/tcp_bbr.c +++ b/net/ipv4/tcp_bbr.c @@ -773,7 +773,9 @@ static void bbr_update_min_rtt(struct so } } } - bbr->idle_restart = 0; + /* Restart after idle ends only once we process a new S/ACK for data */ + if (rs->delivered > 0) + bbr->idle_restart = 0; }
static void bbr_update_model(struct sock *sk, const struct rate_sample *rs)