tcp: fix false reordering signal in tcp_shifted_skb (4c90d3b3) · Commits · 戴 / test

When tcp_shifted_skb() shifts bytes from the skb that is currently pointed to by 'highest_sack' then the increment of TCP_SKB_CB(skb)->seq implicitly advances tcp_highest_sack_seq(). This implicit advancement, combined with the recent fix to pass the correct SACKed range into tcp_sacktag_one(), caused tcp_sacktag_one() to think that the newly SACKed range was before the tcp_highest_sack_seq(), leading to a call to tcp_update_reordering() with a degree of reordering matching the size of the newly SACKed range (typically just 1 packet, which is a NOP, but potentially larger). This commit fixes this by simply calling tcp_sacktag_one() before the TCP_SKB_CB(skb)->seq advancement that can advance our notion of the highest SACKed sequence. Correspondingly, we can simplify the code a little now that tcp_shifted_skb() should update the lost_cnt_hint in all cases where skb == tp->lost_skb_hint. Signed-off-by:

Neal Cardwell <ncardwell@google.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

net/ipv4/tcp_input.c

+10 −8

Original line number	Diff line number	Diff line
		@@ -1403,8 +1403,16 @@ static int tcp_shifted_skb(struct sock sk, struct sk_buff skb,

		BUG_ON(!pcount);

		/* Adjust hint for FACK. Non-FACK is handled in tcp_sacktag_one(). */
		if (tcp_is_fack(tp) && (skb == tp->lost_skb_hint))
		/* Adjust counters and hints for the newly sacked sequence
		* range but discard the return value since prev is already
		* marked. We must tag the range first because the seq
		* advancement below implicitly advances
		* tcp_highest_sack_seq() when skb is highest_sack.
		*/
		tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
		start_seq, end_seq, dup_sack, pcount);

		if (skb == tp->lost_skb_hint)
		tp->lost_cnt_hint += pcount;

		TCP_SKB_CB(prev)->end_seq += shifted;
		@@ -1430,12 +1438,6 @@ static int tcp_shifted_skb(struct sock sk, struct sk_buff skb,
		skb_shinfo(skb)->gso_type = 0;
		}

		/* Adjust counters and hints for the newly sacked sequence range but
		* discard the return value since prev is already marked.
		*/
		tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
		start_seq, end_seq, dup_sack, pcount);

		/* Difference in this won't matter, both ACKed by the same cumul. ACK */
		TCP_SKB_CB(prev)->sacked \|= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);

Admin message