linux-kernel - Re: clocksource mutex deadlock, cat current

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Message-ID: <alpine.LFD.2.00.1002081038430.2811@localhost.localdomain>
Date:	Mon, 8 Feb 2010 11:06:58 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Andreas Mohr <andi@...as.de>
cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	John Stultz <johnstul@...ibm.com>
Subject: Re: clocksource mutex deadlock, cat current_clocksource
 (2.6.33-rc6/7)

On Mon, 8 Feb 2010, Andreas Mohr wrote:
> > Nope, the NMI watchdog is not involved. It merily tells us that the
> > task is stuck.
> 
> OK.
> And after that message debug_locks is zeroed and kwatchdog is gone
> from the process list (probably during debug_locks change).

Oh, no. kwatchdog is a run once thread. It always exits after work is
done, but I'm pretty confused about the NMI watchdog output.

EIP: 0060:[<c1045170>] EFLAGS: 00000082 CPU: 0
EIP is at timekeeping_forward_now+0x116/0x139

I don't see what might make the machine stuck here. Can you decode the
source line with "addr2line -e vmlinux c1045170" please ?

> I'll explain what I think might be happening:
> bootup switches to acpi_pm, timekeeping gets borked, NMI watchdog complains
> due to timekeeping issues, brutally yanks the waiting acpi_pm switchover
> (thereby NOT releasing clocksource_mutex),

No, the NMI watchdog does not yank anything. It just reports.

Thanks,

	tglx
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