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tcp: fix false reordering signal in tcp_shifted_skb

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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>
This commit is contained in:
Neal Cardwell 2012-02-26 10:06:19 +00:00 committed by David S. Miller
parent ecb9719236
commit 4c90d3b303
1 changed files with 10 additions and 8 deletions
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18
net/ipv4/tcp_input.c
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@ -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);