netdev - TCP connection stops after high load.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 11 Apr 2007 11:50:18 -0700
From:	Ben Greear <greearb@...delatech.com>
To:	NetDev <netdev@...r.kernel.org>
Subject: TCP connection stops after high load.

Back in May of last year, I reported this problem, but worked
around it at the time by changing the kernel memory settings
in the networking stack.  I reproduced the problem again today
with the previously working kernel memory settings..which is not
supprising since I just papered over the bug last time.

The problem is that I set up a TCP connection with bi-directional traffic
of around 800Mbps, doing large (20k - 64k writes and reads) between two ports on
the same machine (this 2.6.18.2 kernel is tainted with my full patch set,
but I also reproduced with only the non-tainted send-to-self patch applied
last may on the 2.6.16 kernel, so I assume the bug is not particular to my patch
set).

At first, all is well, but within 5-10 minutes, the TCP connection will stall
and I only see a massive amount of duplicate ACKs on the link.  Before,
I sometimes saw OOM messages, but this time there are no OOM messages.  The system
has a two-port pro/1000 fibre NIC, 1GB RAM, kernel 2.6.18.2 + hacks, etc.
Stopping and starting the connection allows traffic to flow again (if briefly).
Starting a new connection works fine even if the old one is still stalled,
so it's not a global memory exhaustion problem.

So, I would like to dig into this problem myself since no one else
is reporting this type of problem, but I am quite ignorant of the TCP
stack implementation.  Based on the dup-acks I see on the wire, I assume
the TCP state machine is messed up somehow.  Could anyone point me to
likely places in the TCP stack to start looking for this bug?

Thanks,
Ben

-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com

-
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html