Patch "tcp_bbr: reset full pipe detection on loss recovery undo" has been added to the 4.9-stable tree

Patch "tcp_bbr: reset full pipe detection on loss recovery undo" has been added to the 4.9-stable tree

[gregkh]

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;a=summary

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