Hard hang with u3g and -current

[Kostik Belousov]

On Wed, Jun 03, 2009 at 05:52:05PM +1000, Peter Jeremy wrote:
> I have a Huawei E169 3G modem which I'm using with the u3g driver on
> -current/i386 from about 4 weeks ago on my Aspire One (dual-core
> N270).  If I access the stats port (/dev/cuaD0.2) then the system will
> randomly hang.  The problem seems to occur more frequently when I'm
> using X but I've also seen it (once) when I was using a VTY.  I'm not
> using hald.  There doesn't seem to be a problem if I don't access
> /dev/cuaD0.2.
> 
> When the system hangs, the 3G modem hangs up (though this may be the
> keepalive timer expiring at the remote end) and there's no response to
> the keyboard (Ctrl-Alt-Del and Ctrl-Alt-Fn from X; Ctrl-Alt-Esc and
> Alt-Fn from VTY; CapsLock, NumLock in either mode).  The kernel still
> responds to pings over ethernet and I can change brightness via the
> keyboard so SMM is still working.
> 
> Has anyone else seen anything like this?
> 
> Can anyone suggest a way to track this down?  I can't get to DDB, there's
> no serial, firewire, PCcard or similar I/O.

I am not volunteering to do the debugging. I am only to suggest how
to grab the debugging information for this case, that looks like a
deadlock. Since parts of the network stack are functional, add ddb
script to dump neccessary information, and trigger it by receiving
some specially formatted ping packet. I higly suspect that you
need at least backtraces of all threads and information on held
locks.
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