linux-kernel - Re: [crash, bisected] Re: clocksource: Resolve cpu hotplug dead lock with TSC unstable

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Date:	Fri, 11 Sep 2009 09:37:47 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jens Axboe <jens.axboe@...cle.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	John Stultz <johnstul@...ibm.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Galbraith <efault@....de>,
	Con Kolivas <kernel@...ivas.org>, linux-kernel@...r.kernel.org
Subject: Re: [crash, bisected] Re: clocksource: Resolve cpu hotplug dead
	lock with TSC unstable


* Ingo Molnar <mingo@...e.hu> wrote:

> 
> * Ingo Molnar <mingo@...e.hu> wrote:
> 
> > 
> > * Jens Axboe <jens.axboe@...cle.com> wrote:
> > 
> > > I went to try -tip btw, but it crashes on boot. Here's the 
> > > backtrace, typed manually, it's crashing in 
> > > queue_work_on+0x28/0x60.
> > > 
> > > Call Trace:
> > >         queue_work
> > >         schedule_work
> > >         clocksource_mark_unstable
> > >         mark_tsc_unstable
> > >         check_tsc_sync_source
> > >         native_cpu_up
> > >         relay_hotcpu_callback
> > >         do_forK_idle
> > >         _cpu_up
> > >         cpu_up
> > >         kernel_init
> > >         kernel_thread_helper
> > 
> > hm, that looks like an old bug i fixed days ago via:
> > 
> >   00a3273: Revert "x86: Make tsc=reliable override boot time stability checks"
> > 
> > Have you tested tip:master - do you still know which sha1?
> 
> Ok, i reproduced it on a testbox and bisected it, the crash is 
> caused by:
> 
>  7285dd7fd375763bfb8ab1ac9cf3f1206f503c16 is first bad commit
>  commit 7285dd7fd375763bfb8ab1ac9cf3f1206f503c16
>  Author: Thomas Gleixner <tglx@...utronix.de>
>  Date:   Fri Aug 28 20:25:24 2009 +0200
> 
>     clocksource: Resolve cpu hotplug dead lock with TSC unstable
>     
>     Martin Schwidefsky analyzed it:
> 
> I've reverted it in tip/master for now.

and that uncovers the circular locking bug that this commit was 
supposed to fix ...

Martin?

	Ingo
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