netdev - Re: [PATCH] tcp: TCP_USER_TIMEOUT can not work in tcp_probe

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Date:   Mon, 11 Sep 2017 07:49:17 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     liujian56@...wei.com
Cc:     davem@...emloft.net, kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org,
        edumazet@...gle.com, ycheng@...gle.com, hkchu@...gle.com,
        netdev@...r.kernel.org, weiyongjun1@...wei.com
Subject: Re: [PATCH] tcp: TCP_USER_TIMEOUT can not work in tcp_probe_timer()

On Mon, 2017-09-11 at 14:27 +0800, liujian56@...wei.com wrote:
> From: liujian <liujian56@...wei.com>
> 
> After the tcp socket go to ESTABLISHED stat, change IP address (server
> side),
> then the tcp socket will go tcp_probe_timer process.
> 
> [root@...alhost net]# netstat -toe
> Active Internet connections (w/o servers)
> Proto Recv-Q Send-Q Local Address           Foreign Address         State       User       Inode      Timer
> tcp        0   1104 9.81.254:personal-agent 9.84.201.213:23597      ESTABLISHED root       12819      probe (4.36/0/7)
> [root@...alhost net]# cat /proc/net/tcp
>   sl  local_address rem_address   st tx_queue rx_queue tr tm->when retrnsmt   uid  timeout inode                                                     
>    3: B1FE5109:15B3 D5C95409:5C2D 01 00000495:00000000 04:0000005E 00000000     0        7 12819 2 ffff95cdcf45a000 20 4 1 10 -1 
> 
> In my test case, tcp_write_queue_head(sk) and tcp_send_head(sk) is  same
> SKB.
> And ((s32)(tcp_time_stamp(tp) - start_ts) >
> jiffies_to_msecs(icsk->icsk_user_timeout))
>  always is false.

Interesting.

>  Here use keepalive_time_elapsed(tp) to do the compare as
> tcp_keepalive_timer do.


But zero window probe and TCP_USER_TIMEOUT can be used without
keepalives...


A packetdrill test would help, I will write one.

Thanks.