This is a note to let you know that I've just added the patch titled

tcp_bbr: reset full pipe detection on loss recovery undo

to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: tcp_bbr-reset-full-pipe-detection-on-loss-recovery-undo.patch and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 2f6c498e4f15d27852c04ed46d804a39137ba364 Mon Sep 17 00:00:00 2001

From: Neal Cardwell ncardwell@google.com Date: Thu, 7 Dec 2017 12:43:31 -0500 Subject: tcp_bbr: reset full pipe detection on loss recovery undo

From: Neal Cardwell ncardwell@google.com

commit 2f6c498e4f15d27852c04ed46d804a39137ba364 upstream.

Fix BBR so that upon notification of a loss recovery undo BBR resets the full pipe detection (STARTUP exit) state machine.

Under high reordering, reordering events can be interpreted as loss. If the reordering and spurious loss estimates are high enough, this could previously cause BBR to spuriously estimate that the pipe is full.

Since spurious loss recovery means that our overall sending will have slowed down spuriously, this commit gives a flow more time to probe robustly for bandwidth and decide the pipe is really full.

Signed-off-by: Neal Cardwell ncardwell@google.com Reviewed-by: Yuchung Cheng ycheng@google.com Acked-by: Soheil Hassas Yeganeh soheil@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, 4 insertions(+)

--- a/net/ipv4/tcp_bbr.c +++ b/net/ipv4/tcp_bbr.c @@ -843,6 +843,10 @@ static u32 bbr_sndbuf_expand(struct sock */ static u32 bbr_undo_cwnd(struct sock *sk) { + struct bbr *bbr = inet_csk_ca(sk); + + bbr->full_bw = 0; /* spurious slow-down; reset full pipe detection */ + bbr->full_bw_cnt = 0; return tcp_sk(sk)->snd_cwnd; }

Patches currently in stable-queue which might be from ncardwell@google.com are

queue-4.9/tcp_bbr-reset-full-pipe-detection-on-loss-recovery-undo.patch queue-4.9/tcp_bbr-reset-long-term-bandwidth-sampling-on-loss-recovery-undo.patch