lkml.org 
[lkml]   [2016]   [Feb]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 3.13.y-ckt 131/136] tcp_yeah: don't set ssthresh below 2
    Date
    3.13.11-ckt34 -stable review patch.  If anyone has any objections, please let me know.

    ---8<------------------------------------------------------------

    From: Neal Cardwell <ncardwell@google.com>

    [ Upstream commit 83d15e70c4d8909d722c0d64747d8fb42e38a48f ]

    For tcp_yeah, use an ssthresh floor of 2, the same floor used by Reno
    and CUBIC, per RFC 5681 (equation 4).

    tcp_yeah_ssthresh() was sometimes returning a 0 or negative ssthresh
    value if the intended reduction is as big or bigger than the current
    cwnd. Congestion control modules should never return a zero or
    negative ssthresh. A zero ssthresh generally results in a zero cwnd,
    causing the connection to stall. A negative ssthresh value will be
    interpreted as a u32 and will set a target cwnd for PRR near 4
    billion.

    Oleksandr Natalenko reported that a system using tcp_yeah with ECN
    could see a warning about a prior_cwnd of 0 in
    tcp_cwnd_reduction(). Testing verified that this was due to
    tcp_yeah_ssthresh() misbehaving in this way.

    Reported-by: Oleksandr Natalenko <oleksandr@natalenko.name>
    Signed-off-by: Neal Cardwell <ncardwell@google.com>
    Signed-off-by: Yuchung Cheng <ycheng@google.com>
    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    net/ipv4/tcp_yeah.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/net/ipv4/tcp_yeah.c b/net/ipv4/tcp_yeah.c
    index a347a07..9829075 100644
    --- a/net/ipv4/tcp_yeah.c
    +++ b/net/ipv4/tcp_yeah.c
    @@ -223,7 +223,7 @@ static u32 tcp_yeah_ssthresh(struct sock *sk) {
    yeah->fast_count = 0;
    yeah->reno_count = max(yeah->reno_count>>1, 2U);

    - return tp->snd_cwnd - reduction;
    + return max_t(int, tp->snd_cwnd - reduction, 2);
    }

    static struct tcp_congestion_ops tcp_yeah __read_mostly = {
    --
    1.9.1
    \
     
     \ /
      Last update: 2016-02-02 20:01    [W:4.058 / U:0.360 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site