RTS threshold low -> hang

Jouni Malinen jkmaline at cc.hut.fi
Sun Nov 9 20:49:26 EST 2003


On Sat, Nov 08, 2003 at 04:49:19PM +0100, Vaclav Dvorak wrote:

> Because of the hidden-node problem and congestion, I tried setting the 
> RTS threshold to various low values (<100 bytes). This makes the 
> computer hang after a few hours.

Which station firmware version are you using? How actively is the
network being used? Can you easily reproduce this (i.e., if you do not
change RTS threshold, it never hangs, and if you set it, it always
hangs)? How did you verify that the box hung? It did not work in
wireless side? It did not work on wired side? Did you verify whether
only networking was down?

> I'm using hostap 0.1.2 with jbohac's psrrr patch 
> (http://www.jikos.cz/~jbohac/hostap/) for enabling txpower control and 
> keeping txpower after card reset. There is one X-Com XI-626 card in 
> managed mode.

Do you mean that the host that hung was in Master mode and it had one
STA associated with it or that the hang happened on a host that was in
Managed mode?

> netfilter patches. The computer is a Cyrix 6x86MX 150MHz. There are a 
> few messages in the logs some time before the crash:
> 
> Nov  8 02:17:44 server kernel: NETDEV WATCHDOG: wlan0: transmit timed out

Some time before? As in, just before or some random (may be long) time
before?

> The computer normally doesn't have a monitor or a keyboard. I don't know 
> if the kernel spews some useful information on the console when the 
> crash happens - is that likely? Should I bother to carry the monitor to 
> the computer the next time it crashes, and the jot down the numbers on a 
> piece of paper? :-) Or is there anything else I can do to help debug 
> this?

Well, it is a bit difficult to know without checking it once.. ;-) If
the hang is something like NULL pointer dereference in interrupt
context, yes, you would probably have something on the console
(although, I'm not sure why small RTS threshold would trigger this). If
it is hardware failure or a deadlock, you might not get anything on
console.

-- 
Jouni Malinen                                            PGP id EFC895FA



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