From: Denis Du <dudenis2000@yahoo.ca>
Date: Sat, 24 Feb 2018 16:51:42 -0500
Subject: hdlc_ppp: carrier detect ok, don't turn off negotiation
Git-commit: b6c3bad1ba83af1062a7ff6986d9edc4f3d7fc8e
Patch-mainline: v4.16-rc5
References: networking-stable-18_03_07

Sometimes when physical lines have a just good noise to make the protocol
handshaking fail, but the carrier detect still good. Then after remove of
the noise, nobody will trigger this protocol to be start again to cause
the link to never come back. The fix is when the carrier is still on, not
terminate the protocol handshaking.

Signed-off-by: Denis Du <dudenis2000@yahoo.ca>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 drivers/net/wan/hdlc_ppp.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/drivers/net/wan/hdlc_ppp.c
+++ b/drivers/net/wan/hdlc_ppp.c
@@ -574,7 +574,10 @@ static void ppp_timer(unsigned long arg)
 			ppp_cp_event(proto->dev, proto->pid, TO_GOOD, 0, 0,
 				     0, NULL);
 			proto->restart_counter--;
-		} else
+		} else if (netif_carrier_ok(proto->dev))
+			ppp_cp_event(proto->dev, proto->pid, TO_GOOD, 0, 0,
+				     0, NULL);
+		else
 			ppp_cp_event(proto->dev, proto->pid, TO_BAD, 0, 0,
 				     0, NULL);
 		break;