Commit 85369750 authored Dec 27, 2019 by Cambda Zhu Committed by David S. Miller Dec 30, 2019

tcp: Fix highest_sack and highest_sack_seq



>From commit 50895b9d ("tcp: highest_sack fix"), the logic about
setting tp->highest_sack to the head of the send queue was removed.
Of course the logic is error prone, but it is logical. Before we
remove the pointer to the highest sack skb and use the seq instead,
we need to set tp->highest_sack to NULL when there is no skb after
the last sack, and then replace NULL with the real skb when new skb
inserted into the rtx queue, because the NULL means the highest sack
seq is tp->snd_nxt. If tp->highest_sack is NULL and new data sent,
the next ACK with sack option will increase tp->reordering unexpectedly.

This patch sets tp->highest_sack to the tail of the rtx queue if
it's NULL and new data is sent. The patch keeps the rule that the
highest_sack can only be maintained by sack processing, except for
this only case.

Fixes: 50895b9d ("tcp: highest_sack fix")
Signed-off-by: Cambda Zhu <cambda@linux.alibaba.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent a33121e5

net/ipv4/tcp_output.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -72,6 +72,9 @@ static void tcp_event_new_data_sent(struct sock sk, struct sk_buff skb)
		__skb_unlink(skb, &sk->sk_write_queue);
		tcp_rbtree_insert(&sk->tcp_rtx_queue, skb);

		if (tp->highest_sack == NULL)
		tp->highest_sack = skb;

		tp->packets_out += tcp_skb_pcount(skb);
		if (!prior_packets \|\| icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)
		tcp_rearm_rto(sk);

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