Messages in this thread Patch in this message | | | Date | Fri, 16 Mar 2012 16:38:29 -0700 | From | Greg KH <> | Subject | [ 19/41] tcp: fix false reordering signal in tcp_shifted_skb |
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3.2-stable review patch. If anyone has any objections, please let me know.
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From: Neal Cardwell <ncardwell@google.com>
[ Upstream commit 4c90d3b30334833450ccbb02f452d4972a3c3c3f ]
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> Acked-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- net/ipv4/tcp_input.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-)
--- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -1406,8 +1406,16 @@ static int tcp_shifted_skb(struct sock * 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; @@ -1433,12 +1441,6 @@ static int tcp_shifted_skb(struct sock * 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);
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