Commit 83ca28be authored Sep 22, 2005 by Herbert Xu Committed by David S. Miller Sep 22, 2005

[TCP]: Adjust Reno SACK estimate in tcp_fragment



Since the introduction of TSO pcount a year ago, it has been possible
for tcp_fragment() to cause packets_out to decrease.  Prior to that,
tcp_retrans_try_collapse() was the only way for that to happen on the
retransmission path.

When this happens with Reno, it is possible for sasked_out to become
invalid because it is only an estimate and not tied to any particular
packet on the retransmission queue.

Therefore we need to adjust sacked_out as well as left_out in the Reno
case.  The following patch does exactly that.

This bug is pretty difficult to trigger in practice though since you
need a SACKless peer with a retransmission that occurs just as the
cached MTU value expires.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent e484585e

net/ipv4/tcp_output.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -509,7 +509,16 @@ int tcp_fragment(struct sock sk, struct sk_buff skb, u32 len, unsigned int mss
		tp->lost_out -= diff;
		tp->left_out -= diff;
		}

		if (diff > 0) {
		/* Adjust Reno SACK estimate. */
		if (!tp->rx_opt.sack_ok) {
		tp->sacked_out -= diff;
		if ((int)tp->sacked_out < 0)
		tp->sacked_out = 0;
		tcp_sync_left_out(tp);
		}

		tp->fackets_out -= diff;
		if ((int)tp->fackets_out < 0)
		tp->fackets_out = 0;