tcp: fix DSACK-based undo on non-duplicate ACK

Fixes DSACK-based undo when sender is in Open State and
an ACK advances snd_una.

Example scenario:
- Sender goes into recovery and makes some spurious rtx.
- It comes out of recovery and enters into open state.
- It sends some more packets, let's say 4.
- The receiver sends an ACK for the first two, but this ACK is lost.
- The sender receives ack for first two, and DSACK for previous
  spurious rtx.

Signed-off-by: Priyaranjan Jha <priyarjha@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Yousuk Seung <ysseung@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 5a87a00641d3a82bfb78d4f3a2959fe8ea2e119c..b2fc7163bd402407ae656de841aebf538ca1a326 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -115,7 +115,7 @@ int sysctl_tcp_invalid_ratelimit __read_mostly = HZ/2;
 
 #define FLAG_ACKED             (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
 #define FLAG_NOT_DUP           (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
-#define FLAG_CA_ALERT          (FLAG_DATA_SACKED|FLAG_ECE)
+#define FLAG_CA_ALERT          (FLAG_DATA_SACKED|FLAG_ECE|FLAG_DSACKING_ACK)
 #define FLAG_FORWARD_PROGRESS  (FLAG_ACKED|FLAG_DATA_SACKED)
 
 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)