Messages in this thread | | | From | Eric Dumazet <> | Date | Mon, 14 Dec 2020 18:42:42 +0100 | Subject | Re: [net-next PATCH v3] tcp: Add logic to check for SYN w/ data in tcp_simple_retransmit |
| |
On Sat, Dec 12, 2020 at 9:31 PM Alexander Duyck <alexander.duyck@gmail.com> wrote: > > From: Alexander Duyck <alexanderduyck@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 <alexanderduyck@fb.com> > --- >
SGTM, thanks !
Signed-off-by: Eric Dumazet <edumazet@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 >
| |