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Message-ID: <CANn89iK0g7uqduiAMZ0jax4_Y+P=0pJUArsd=LAhAHa2j+gRAg@mail.gmail.com>
Date: Mon, 30 Dec 2024 10:33:33 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: "Dujeong.lee" <dujeong.lee@...sung.com>
Cc: Youngmin Nam <youngmin.nam@...sung.com>, Jakub Kicinski <kuba@...nel.org>,
Neal Cardwell <ncardwell@...gle.com>, davem@...emloft.net, dsahern@...nel.org,
pabeni@...hat.com, horms@...nel.org, guo88.liu@...sung.com,
yiwang.cai@...sung.com, netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
joonki.min@...sung.com, hajun.sung@...sung.com, d7271.choe@...sung.com,
sw.ju@...sung.com, iamyunsu.kim@...sung.com, kw0619.kim@...sung.com,
hsl.lim@...sung.com, hanbum22.lee@...sung.com, chaemoo.lim@...sung.com,
seungjin1.yu@...sung.com
Subject: Re: [PATCH] tcp: check socket state before calling WARN_ON
On Mon, Dec 30, 2024 at 1:24 AM Dujeong.lee <dujeong.lee@...sung.com> wrote:
>
> On Wed, Dec 18, 2024 7:28 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> > On Wed, Dec 18, 2024 at 11:18 AM Dujeong.lee <dujeong.lee@...sung.com>
> > wrote:
> > >
> > > Tue, December 10, 2024 at 4:10 PM Dujeong Lee wrote:
> > > > On Tue, Dec 10, 2024 at 12:39 PM Dujeong Lee wrote:
> > > > > On Mon, Dec 9, 2024 at 7:21 PM Eric Dumazet <edumazet@...gle.com>
> > wrote:
> > > > > > On Mon, Dec 9, 2024 at 11:16 AM Dujeong.lee
> > > > > > <dujeong.lee@...sung.com>
> > > > > > wrote:
> > > > > > >
> > > > > >
> > > > > > > Thanks for all the details on packetdrill and we are also
> > > > > > > exploring
> > > > > > USENIX 2013 material.
> > > > > > > I have one question. The issue happens when DUT receives TCP
> > > > > > > ack with
> > > > > > large delay from network, e.g., 28seconds since last Tx. Is
> > > > > > packetdrill able to emulate this network delay (or congestion)
> > > > > > in script
> > > > > level?
> > > > > >
> > > > > > Yes, the packetdrill scripts can wait an arbitrary amount of
> > > > > > time between each event
> > > > > >
> > > > > > +28 <next event>
> > > > > >
> > > > > > 28 seconds seems okay. If the issue was triggered after 4 days,
> > > > > > packetdrill would be impractical ;)
> > > > >
> > > > > Hi all,
> > > > >
> > > > > We secured new ramdump.
> > > > > Please find the below values with TCP header details.
> > > > >
> > > > > tp->packets_out = 0
> > > > > tp->sacked_out = 0
> > > > > tp->lost_out = 1
> > > > > tp->retrans_out = 1
> > > > > tp->rx_opt.sack_ok = 5 (tcp_is_sack(tp)) mss_cache = 1400
> > > > > ((struct inet_connection_sock *)sk)->icsk_ca_state = 4 ((struct
> > > > > inet_connection_sock *)sk)->icsk_pmtu_cookie = 1500
> > > > >
> > > > > Hex from ip header:
> > > > > 45 00 00 40 75 40 00 00 39 06 91 13 8E FB 2A CA C0 A8 00 F7 01 BB
> > > > > A7 CC 51
> > > > > F8 63 CC 52 59 6D A6 B0 10 04 04 77 76 00 00 01 01 08 0A 89 72 C8
> > > > > 42
> > > > > 62 F5
> > > > > F5 D1 01 01 05 0A 52 59 6D A5 52 59 6D A6
> > > > >
> > > > > Transmission Control Protocol
> > > > > Source Port: 443
> > > > > Destination Port: 42956
> > > > > TCP Segment Len: 0
> > > > > Sequence Number (raw): 1375232972
> > > > > Acknowledgment number (raw): 1381592486
> > > > > 1011 .... = Header Length: 44 bytes (11)
> > > > > Flags: 0x010 (ACK)
> > > > > Window: 1028
> > > > > Calculated window size: 1028
> > > > > Urgent Pointer: 0
> > > > > Options: (24 bytes), No-Operation (NOP), No-Operation (NOP),
> > > > > Timestamps, No-Operation (NOP), No-Operation (NOP), SACK
> > > > >
> > > > > If anyone wants to check other values, please feel free to ask me
> > > > >
> > > > > Thanks,
> > > > > Dujeong.
> > > >
> > > > I have a question.
> > > >
> > > > From the latest ramdump I could see that
> > > > 1) tcp_sk(sk)->packets_out = 0
> > > > 2) inet_csk(sk)->icsk_backoff = 0
> > > > 3) sk_write_queue.len = 0
> > > > which suggests that tcp_write_queue_purge was indeed called.
> > > >
> > > > Noting that:
> > > > 1) tcp_write_queue_purge reset packets_out to 0 and
> > > > 2) in_flight should be non-negative where in_flight = packets_out -
> > > > left_out + retrans_out, what if we reset left_out and retrans_out as
> > > > well in tcp_write_queue_purge?
> > > >
> > > > Do we see any potential issue with this?
> > >
> > > Hello Eric and Neal.
> > >
> > > It is a gentle reminder.
> > > Could you please review the latest ramdump values and and question?
> >
> > It will have to wait next year, Neal is OOO.
> >
> > I asked a packetdrill reproducer, I can not spend days working on an issue
> > that does not trigger in our production hosts.
> >
> > Something could be wrong in your trees, or perhaps some eBPF program
> > changing the state of the socket...
>
> Hi Eric
>
> I tried to make packetdrill script for local mode, which injects delayed acks for data and FIN after close.
>
> // Test basic connection teardown where local process closes first:
> // the local process calls close() first, so we send a FIN.
> // Then we receive an delayed ACK for data and FIN.
> // Then we receive a FIN and ACK it.
>
> `../common/defaults.sh`
> 0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 // Create socket
> +.01...0.011 connect(3, ..., ...) = 0 // Initiate connection
> +0 > S 0:0(0) <...> // Send SYN
> +0 < S. 0:0(0) ack 1 win 32768 <mss 1000,nop,wscale 6,nop,nop,sackOK> // Receive SYN-ACK with TCP options
> +0 > . 1:1(0) ack 1 // Send ACK
>
> +0 write(3, ..., 1000) = 1000 // Write 1000 bytes
> +0 > P. 1:1001(1000) ack 1 // Send data with PSH flag
>
> +0 close(3) = 0 // Local side initiates close
> +0 > F. 1001:1001(0) ack 1 // Send FIN
> +1 < . 1:1(0) ack 1001 win 257 // Receive ACK for data
> +0 < . 1:1(0) ack 1002 win 257 // Receive ACK for FIN
>
> +0 < F. 1:1(0) ack 1002 win 257 // Receive FIN from remote
> +0 > . 1002:1002(0) ack 2 // Send ACK for FIN
>
>
> But got below error when I run the script.
>
> $ sudo ./packetdrill ../tcp/close/close-half-delayed-ack.pkt
> ../tcp/close/close-half-delayed-ack.pkt:22: error handling packet: live packet field tcp_fin: expected: 0 (0x0) vs actual: 1 (0x1)
> script packet: 1.010997 . 1002:1002(0) ack 2
> actual packet: 0.014840 F. 1001:1001(0) ack 1 win 256
This means the FIN was retransmited earlier.
Then the data segment was probably also retransmit.
You can use "tcpdump -i any &" while developing your script.
0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
// Create socket
+.01...0.111 connect(3, ..., ...) = 0
// Initiate connection
+0 > S 0:0(0) <...>
// Send SYN
+.1 < S. 0:0(0) ack 1 win 32768 <mss 1000,nop,wscale
6,nop,nop,sackOK> // Receive SYN-ACK with TCP options
+0 > . 1:1(0) ack 1
// Send ACK
+0 write(3, ..., 1000) = 1000
// Write 1000 bytes
+0 > P. 1:1001(1000) ack 1
// Send data with PSH flag
+0 close(3) = 0
// Local side initiates close
+0 > F. 1001:1001(0) ack 1
// Send FIN
+.2 > F. 1001:1001(0) ack 1 // FIN retransmit
+.2~+.4 > P. 1:1001(1000) ack 1 // RTX
+0 < . 1:1(0) ack 1001 win 257
// Receive ACK for data
+0 > F. 1001:1001(0) ack 1 // FIN retransmit
+0 < . 1:1(0) ack 1002 win 257
// Receive ACK for FIN
+0 < F. 1:1(0) ack 1002 win 257
// Receive FIN from remote
+0 > . 1002:1002(0) ack 2
// Send ACK for FIN
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