Re: how to debug a deadlock'ed kernel?

From: george anzinger (
Date: Tue Dec 11 2001 - 16:41:44 EST

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.

Real time sched:
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This archive was generated by hypermail 2b29 : Sat Dec 15 2001 - 21:00:21 EST