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Date: Mon, 8 Feb 2010 10:13:00 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Andreas Mohr <andi@lisas.de>
cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
       John Stultz <johnstul@us.ibm.com>
Subject: Re: clocksource mutex deadlock, cat current_clocksource
 (2.6.33-rc6/7)
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On Mon, 8 Feb 2010, Andreas Mohr wrote:
> 
> And then a cat current_clocksource managed to hang again.

Well, that's not surprising at all. If one task is stuck on clocksource_mutex,
then the next one will be stuck as well.

> (NOTE that the - now complete! - SysRq-T list does NOT show any backtraces
> of kwatchdog any more, only many other processes)
> Could it be that the (rather disruptive) NMI watchdog confuses the current state at
> change_clocksource and causes that stuff to get left with
> clocksource_mutex remaining taken?

Nope, the NMI watchdog is not involved. It merily tells us that the
task is stuck.

      tglx