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[Ben Howard <ben.howard@xxxxxxxxxxxxx>]

Fix is confirmed by a Canonical partner.

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https://bugs.launchpad.net/bugs/1390604

Title:
  Outbound TCP Throughput drops to zero for several drivers

Status in linux package in Ubuntu:
  Fix Released
Status in linux source package in Utopic:
  Fix Committed
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:
  https://patchwork.ozlabs.org/patch/405110/

  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)) {
                  NET_INC_STATS_BH(sock_net(sk),
                                   LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
                  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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