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[Bug 1390604] Re: Outbound TCP Throughput drops to zero for several drivers


Luis already has this applied in his queue:

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  Outbound TCP Throughput drops to zero for several drivers

Status in “linux” package in Ubuntu:
  Fix Released
Status in “linux” source package in Utopic:
  In Progress
Status in “linux” source package in Vivid:
  Fix Released

Bug description:
  There is a bug with TCP in kernel 3.16+ described as:

  "Some drivers are unable to perform TX completions in a bound time.
  They instead call skb_orphan()

  Problem is skb_fclone_busy() has to detect this case, otherwise
  we block TCP retransmits and can freeze unlucky tcp sessions on
  mostly idle hosts."

  A patch for this has been submitted upstream:

  The Google engineer that submitted that patch also adds the following:

  Backported patch for 3.16 or 3.17 kernel is much simpler :

  diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
  index 4e4932b5079b..a8794367cd20 100644
  --- a/net/ipv4/tcp_output.c
  +++ b/net/ipv4/tcp_output.c
  @@ -2082,7 +2082,8 @@ static bool skb_still_in_host_queue(const struct sock *sk,
          const struct sk_buff *fclone = skb + 1;
          if (unlikely(skb->fclone == SKB_FCLONE_ORIG &&
  -                    fclone->fclone == SKB_FCLONE_CLONE)) {
  +                    fclone->fclone == SKB_FCLONE_CLONE &&
  +                    fclone->sk == sk)) {
                  return true;

  I do not believe that this problem affects any release prior to 14.10, and I don't know which version of the patch you may need, but have included both.

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