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    Subject[PATCH 3.13 004/162] tcp: don't use timestamp from repaired skb-s to calculate RTT (v2)
    Date
    3.13.11.11 -stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Andrey Vagin <avagin@openvz.org>

    [ Upstream commit 9d186cac7ffb1831e9f34cb4a3a8b22abb9dd9d4 ]

    We don't know right timestamp for repaired skb-s. Wrong RTT estimations
    isn't good, because some congestion modules heavily depends on it.

    This patch adds the TCPCB_REPAIRED flag, which is included in
    TCPCB_RETRANS.

    Thanks to Eric for the advice how to fix this issue.

    This patch fixes the warning:
    [ 879.562947] WARNING: CPU: 0 PID: 2825 at net/ipv4/tcp_input.c:3078 tcp_ack+0x11f5/0x1380()
    [ 879.567253] CPU: 0 PID: 2825 Comm: socket-tcpbuf-l Not tainted 3.16.0-next-20140811 #1
    [ 879.567829] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
    [ 879.568177] 0000000000000000 00000000c532680c ffff880039643d00 ffffffff817aa2d2
    [ 879.568776] 0000000000000000 ffff880039643d38 ffffffff8109afbd ffff880039d6ba80
    [ 879.569386] ffff88003a449800 000000002983d6bd 0000000000000000 000000002983d6bc
    [ 879.569982] Call Trace:
    [ 879.570264] [<ffffffff817aa2d2>] dump_stack+0x4d/0x66
    [ 879.570599] [<ffffffff8109afbd>] warn_slowpath_common+0x7d/0xa0
    [ 879.570935] [<ffffffff8109b0ea>] warn_slowpath_null+0x1a/0x20
    [ 879.571292] [<ffffffff816d0a05>] tcp_ack+0x11f5/0x1380
    [ 879.571614] [<ffffffff816d10bd>] tcp_rcv_established+0x1ed/0x710
    [ 879.571958] [<ffffffff816dc9da>] tcp_v4_do_rcv+0x10a/0x370
    [ 879.572315] [<ffffffff81657459>] release_sock+0x89/0x1d0
    [ 879.572642] [<ffffffff816c81a0>] do_tcp_setsockopt.isra.36+0x120/0x860
    [ 879.573000] [<ffffffff8110a52e>] ? rcu_read_lock_held+0x6e/0x80
    [ 879.573352] [<ffffffff816c8912>] tcp_setsockopt+0x32/0x40
    [ 879.573678] [<ffffffff81654ac4>] sock_common_setsockopt+0x14/0x20
    [ 879.574031] [<ffffffff816537b0>] SyS_setsockopt+0x80/0xf0
    [ 879.574393] [<ffffffff817b40a9>] system_call_fastpath+0x16/0x1b
    [ 879.574730] ---[ end trace a17cbc38eb8c5c00 ]---

    v2: moving setting of skb->when for repaired skb-s in tcp_write_xmit,
    where it's set for other skb-s.

    Fixes: 431a91242d8d ("tcp: timestamp SYN+DATA messages")
    Fixes: 740b0f1841f6 ("tcp: switch rtt estimations to usec resolution")
    Cc: Eric Dumazet <edumazet@google.com>
    Cc: Pavel Emelyanov <xemul@parallels.com>
    Cc: "David S. Miller" <davem@davemloft.net>
    Signed-off-by: Andrey Vagin <avagin@openvz.org>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    include/net/tcp.h | 4 +++-
    net/ipv4/tcp.c | 14 +++++++-------
    net/ipv4/tcp_output.c | 5 ++++-
    3 files changed, 14 insertions(+), 9 deletions(-)

    diff --git a/include/net/tcp.h b/include/net/tcp.h
    index 920fc2e..0a00e7c 100644
    --- a/include/net/tcp.h
    +++ b/include/net/tcp.h
    @@ -720,8 +720,10 @@ struct tcp_skb_cb {
    #define TCPCB_SACKED_RETRANS 0x02 /* SKB retransmitted */
    #define TCPCB_LOST 0x04 /* SKB is lost */
    #define TCPCB_TAGBITS 0x07 /* All tag bits */
    +#define TCPCB_REPAIRED 0x10 /* SKB repaired (no skb_mstamp) */
    #define TCPCB_EVER_RETRANS 0x80 /* Ever retransmitted frame */
    -#define TCPCB_RETRANS (TCPCB_SACKED_RETRANS|TCPCB_EVER_RETRANS)
    +#define TCPCB_RETRANS (TCPCB_SACKED_RETRANS|TCPCB_EVER_RETRANS| \
    + TCPCB_REPAIRED)

    __u8 ip_dsfield; /* IPv4 tos or IPv6 dsfield */
    /* 1 byte hole */
    diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
    index e7a02d8..e06e1df 100644
    --- a/net/ipv4/tcp.c
    +++ b/net/ipv4/tcp.c
    @@ -1132,13 +1132,6 @@ new_segment:
    goto wait_for_memory;

    /*
    - * All packets are restored as if they have
    - * already been sent.
    - */
    - if (tp->repair)
    - TCP_SKB_CB(skb)->when = tcp_time_stamp;
    -
    - /*
    * Check whether we can use HW checksum.
    */
    if (sk->sk_route_caps & NETIF_F_ALL_CSUM)
    @@ -1147,6 +1140,13 @@ new_segment:
    skb_entail(sk, skb);
    copy = size_goal;
    max = size_goal;
    +
    + /* All packets are restored as if they have
    + * already been sent. skb_mstamp isn't set to
    + * avoid wrong rtt estimation.
    + */
    + if (tp->repair)
    + TCP_SKB_CB(skb)->sacked |= TCPCB_REPAIRED;
    }

    /* Try to append data to the end of skb. */
    diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
    index e3688a4..fa5b391 100644
    --- a/net/ipv4/tcp_output.c
    +++ b/net/ipv4/tcp_output.c
    @@ -1856,8 +1856,11 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
    tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
    BUG_ON(!tso_segs);

    - if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE)
    + if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
    + /* "when" is used as a start point for the retransmit timer */
    + TCP_SKB_CB(skb)->when = tcp_time_stamp;
    goto repair; /* Skip network transmission */
    + }

    cwnd_quota = tcp_cwnd_test(tp, skb);
    if (!cwnd_quota) {
    --
    1.9.1


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