On Mon, Dec 14, 2020 at 9:42 AM Eric Dumazet <eduma...@google.com> wrote: > > On Sat, Dec 12, 2020 at 9:31 PM Alexander Duyck > <alexander.du...@gmail.com> wrote: > > > > From: Alexander Duyck <alexanderdu...@fb.com> > > > > There are cases where a fastopen SYN may trigger either a ICMP_TOOBIG > > message in the case of IPv6 or a fragmentation request in the case of > > IPv4. This results in the socket stalling for a second or more as it does > > not respond to the message by retransmitting the SYN frame. > > > > Normally a SYN frame should not be able to trigger a ICMP_TOOBIG or > > ICMP_FRAG_NEEDED however in the case of fastopen we can have a frame that > > makes use of the entire MSS. In the case of fastopen it does, and an > > additional complication is that the retransmit queue doesn't contain the > > original frames. As a result when tcp_simple_retransmit is called and > > walks the list of frames in the queue it may not mark the frames as lost > > because both the SYN and the data packet each individually are smaller than > > the MSS size after the adjustment. This results in the socket being stalled > > until the retransmit timer kicks in and forces the SYN frame out again > > without the data attached. > > > > In order to resolve this we can reduce the MSS the packets are compared > > to in tcp_simple_retransmit to -1 for cases where we are still in the > > TCP_SYN_SENT state for a fastopen socket. Doing this we will mark all of > > the packets related to the fastopen SYN as lost. > > > > Signed-off-by: Alexander Duyck <alexanderdu...@fb.com> > > --- > > > > SGTM, thanks ! > > Signed-off-by: Eric Dumazet <eduma...@google.com> Nice work. I tested and verified it works with our packetdrill
Signed-off-by: Yuchung Cheng <ych...@google.com> > > > v2: Changed logic to invalidate all retransmit queue frames if fastopen SYN > > v3: Updated commit message to reflect actual solution in 3rd paragraph > >
