Commit ccd0628f authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

tcp: tcp_sack_new_ofo_skb() should be more conservative 



Currently, tcp_sack_new_ofo_skb() sends an ack if prior
acks were 'compressed', if room has to be made in tp->selective_acks[]

But there is no guarantee all four sack ranges can be included
in SACK option. As a matter of fact, when TCP timestamps option
is used, only three SACK ranges can be included.

Lets assume only two ranges can be included, and force the ack:

- When we touch more than 2 ranges in the reordering
  done if tcp_sack_extend() could be done.

- If we have at least 2 ranges when adding a new one.

This enforces that before a range is in third or fourth
position, at least one ACK packet included it in first/second
position.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Acked-by: default avatarSoheil Hassas Yeganeh <soheil@google.com>
Acked-by: default avatarNeal Cardwell <ncardwell@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 2b195850

net/ipv4/tcp_input.c

+11 −1
Original line number Diff line number Diff line
@@ -4348,6 +4348,12 @@ static void tcp_sack_compress_send_ack(struct sock *sk) 
	tcp_send_ack(sk);

}



/* Reasonable amount of sack blocks included in TCP SACK option

 * The max is 4, but this becomes 3 if TCP timestamps are there.

 * Given that SACK packets might be lost, be conservative and use 2.

 */

#define TCP_SACK_BLOCKS_EXPECTED 2



static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)

{

	struct tcp_sock *tp = tcp_sk(sk);
@@ -4360,6 +4366,8 @@ static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq) 


	for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {

		if (tcp_sack_extend(sp, seq, end_seq)) {

			if (this_sack >= TCP_SACK_BLOCKS_EXPECTED)

				tcp_sack_compress_send_ack(sk);

			/* Rotate this_sack to the first one. */

			for (; this_sack > 0; this_sack--, sp--)

				swap(*sp, *(sp - 1));
@@ -4369,6 +4377,9 @@ static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq) 
		}

	}



	if (this_sack >= TCP_SACK_BLOCKS_EXPECTED)

		tcp_sack_compress_send_ack(sk);



	/* Could not find an adjacent existing SACK, build a new one,

	 * put it at the front, and shift everyone else down.  We

	 * always know there is at least one SACK present already here.
@@ -4376,7 +4387,6 @@ static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq) 
	 * If the sack array is full, forget about the last one.

	 */

	if (this_sack >= TCP_NUM_SACKS) {

		tcp_sack_compress_send_ack(sk);

		this_sack--;

		tp->rx_opt.num_sacks--;

		sp--;

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