Re: how to debug a deadlock'ed kernel?

From: Oliver Xymoron (
Date: Tue Dec 11 2001 - 19:25:17 EST

On Tue, 11 Dec 2001, Brian Horton wrote:

> Thanks, I'll try the nmi_watchdog option out. It appears to not be in
> the 2.2.14 kernel, but is in a 2.2.19 kernel that I have from RedHat.

It's there by default in SMP, you just have to enable it with
nmiwatchdog=1 at boot (or something). I didn't mention it because it
probably won't help your problem: as you can use the magic sysrq keys to
reboot, you are not deadlocked with interrupts off, therefore the timer
interrupt will keep the NMI watchdog from ever firing. NMI watchdog is
mostly of use when you can't even get the capslock light to toggle..

> > > 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...

 "Love the dolphins," she advised him. "Write by W.A.S.T.E.."

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