linux-kernel - RE: [PATCH] tcp: check socket state before calling WARN

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Message-ID: <000001db5136$336b1060$9a413120$@samsung.com>
Date: Wed, 18 Dec 2024 19:18:36 +0900
From: "Dujeong.lee" <dujeong.lee@...sung.com>
To: "'Eric Dumazet'" <edumazet@...gle.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

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?

Thanks,
Dujeong.