Re: how to debug a deadlock'ed kernel?

george anzinger (george@mvista.com)
Tue, 11 Dec 2001 13:41:44 -0800

Brian Horton wrote:
>
> Anyone got any good tips on how to debug a SMP system that is locked up
> in a deadlock situation in the kernel? I'm working on a kernel module,
> and after some number of hours of stress testing, the box locks up. None
> of the sysrq options show anything on the display, though the reBoot
> option does reboot the system. RedHat 6.2 and its 2.2.14 kernel. Doesn't
> hang for me on 2.4, so I need to debug it here...
>
> Any hints?

First read about the NMI boot option in Documentation/nmi_watchdog.txt.
If you have this turned on and are not oopsing, then the timer (at
least) is interrupting. The next step I would take would be to used
either kdb (no experience) or kgdb. I have my own version of this if
you are interested. It does, however, require an RS232 (serial)
connection to a host machine.

I don't know about kdb, but kgdb (my version) uses the NMI to trap the
other cpus and also traps NMIs on the way to oopsing.

-- 
George           george@mvista.com
High-res-timers: http://sourceforge.net/projects/high-res-timers/
Real time sched: http://sourceforge.net/projects/rtsched/
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