tcp: undo_retrans counter fixes (c24f691b) · Commits · 戴 / test

Fix a bug that undo_retrans is incorrectly decremented when undo_marker is not set or undo_retrans is already 0. This happens when sender receives more DSACK ACKs than packets retransmitted during the current undo phase. This may also happen when sender receives DSACK after the undo operation is completed or cancelled. Fix another bug that undo_retrans is incorrectly incremented when sender retransmits an skb and tcp_skb_pcount(skb) > 1 (TSO). This case is rare but not impossible. Signed-off-by:

Yuchung Cheng <ycheng@google.com> Acked-by:

Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by:

David S. Miller <davem@davemloft.net>

net/ipv4/tcp_input.c

+3 −2

Original line number	Diff line number	Diff line
		@@ -1222,7 +1222,7 @@ static int tcp_check_dsack(struct sock sk, struct sk_buff ack_skb,
		}

		/* D-SACK for already forgotten data... Do dumb counting. */
		if (dup_sack &&
		if (dup_sack && tp->undo_marker && tp->undo_retrans &&
		!after(end_seq_0, prior_snd_una) &&
		after(end_seq_0, tp->undo_marker))
		tp->undo_retrans--;
		@@ -1299,7 +1299,8 @@ static u8 tcp_sacktag_one(struct sk_buff skb, struct sock sk,

		/* Account D-SACK for retransmitted packet. */
		if (dup_sack && (sacked & TCPCB_RETRANS)) {
		if (after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker))
		if (tp->undo_marker && tp->undo_retrans &&
		after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker))
		tp->undo_retrans--;
		if (sacked & TCPCB_SACKED_ACKED)
		state->reord = min(fack_count, state->reord);

net/ipv4/tcp_output.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -2162,7 +2162,7 @@ int tcp_retransmit_skb(struct sock sk, struct sk_buff skb)
		if (!tp->retrans_stamp)
		tp->retrans_stamp = TCP_SKB_CB(skb)->when;

		tp->undo_retrans++;
		tp->undo_retrans += tcp_skb_pcount(skb);

		/* snd_nxt is stored to detect loss of retransmitted segment,
		* see tcp_input.c tcp_sacktag_write_queue().

Admin message