| Message ID | 160780498125.3272.15437756269539236825.stgit@localhost.localdomain |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [net-next,v3] tcp: Add logic to check for SYN w/ data in tcp_simple_retransmit | expand |
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 >
On Mon, Dec 14, 2020 at 9:42 AM Eric Dumazet <edumazet@google.com> wrote: > > 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> Nice work. I tested and verified it works with our packetdrill Signed-off-by: Yuchung Cheng <ycheng@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 > >
Hello: This patch was applied to netdev/net-next.git (refs/heads/master): On Sat, 12 Dec 2020 12:31:24 -0800 you 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. > > [...] Here is the summary with links: - [net-next,v3] tcp: Add logic to check for SYN w/ data in tcp_simple_retransmit https://git.kernel.org/netdev/net-next/c/c31b70c9968f You are awesome, thank you! -- Deet-doot-dot, I am a bot. https://korg.docs.kernel.org/patchwork/pwbot.html
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 9e8a6c1aa019..e44327a39a1f 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -2688,7 +2688,22 @@ void tcp_simple_retransmit(struct sock *sk) const struct inet_connection_sock *icsk = inet_csk(sk); struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *skb; - unsigned int mss = tcp_current_mss(sk); + int mss; + + /* A fastopen SYN request is stored as two separate packets within + * the retransmit queue, this is done by tcp_send_syn_data(). + * As a result simply checking the MSS of the frames in the queue + * will not work for the SYN packet. + * + * Us being here is an indication of a path MTU issue so we can + * assume that the fastopen SYN was lost and just mark all the + * frames in the retransmit queue as lost. We will use an MSS of + * -1 to mark all frames as lost, otherwise compute the current MSS. + */ + if (tp->syn_data && sk->sk_state == TCP_SYN_SENT) + mss = -1; + else + mss = tcp_current_mss(sk); skb_rbtree_walk(skb, &sk->tcp_rtx_queue) { if (tcp_skb_seglen(skb) > mss)