tcp_bbr: reset full pipe detection on loss recovery undo

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 <[email protected]> Reviewed-by: Yuchung Cheng <[email protected]> Acked-by: Soheil Hassas Yeganeh <[email protected]> Signed-off-by: David S. Miller <[email protected]>
jbg · Dec 8, 2017 · 2f6c498 · 2f6c498
1 parent c589e69
commit 2f6c498
Showing 1 changed file with 4 additions and 0 deletions.
diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c
@@ -874,6 +874,10 @@ static u32 bbr_sndbuf_expand(struct sock *sk)
  */
 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;
 }