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Date:	Fri, 20 Jun 2008 12:41:04 -0500
From:	Travis Stratman <>
To:	Evgeniy Polyakov <>
Subject: Re: data received but not detected

On Fri, 2008-06-20 at 21:25 +0400, Evgeniy Polyakov wrote:
> On Fri, Jun 20, 2008 at 12:10:59PM -0500, Travis Stratman ( wrote:
> > Initially the application was just using a blocking recvfrom() call. I
> > changed to poll() and non-blocking recvfrom (MSG_DONTWAIT) today, and
> > poll() always times out when the lockup occurs. I also tried using an
> Can you confirm that IPSTATS_MIB_INRECEIVES MIB does not increase when
> packets are sent to the frozen machine, but userspace does not receive
> it?

I will come up with a way to test for this in the application.

> Please also clarify this bit again: you see packets in tcpdump running
> on receiving (frozen) host, but do not see them in userspace? After this
> freeze happend system recvmsg/poll calls do not respond until some
> activity on NIC happend? I.e. recv/poll 'unfreeze' only when something
> is received (arp, icmp reply) or after sending too?

I see the packets being sent in tcpdump from the sending application,
but they don't show up in the receiving side until something else comes
in behind them. For example if you look at the client and server trace
that I sent yesterday side by side you will see how the timings line up.
The same packets are shown in each trace. Data needs to be received by
the board to unlock it, sending does not seem to have any effect.

I appreciate the help.


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