linux-kernel - Re: [boot crash] Re: [tip:timers/core] clocksource: Resolve cpu hotplug dead lock with TSC unstable

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Message-ID: <20090903185806.GA5949@elte.hu>
Date:	Thu, 3 Sep 2009 20:58:06 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Martin Schwidefsky <schwidefsky@...ibm.com>, mingo@...hat.com,
	hpa@...or.com, linux-kernel@...r.kernel.org, johnstul@...ibm.com,
	linux-tip-commits@...r.kernel.org
Subject: Re: [boot crash] Re: [tip:timers/core] clocksource: Resolve cpu
	hotplug dead lock with TSC unstable


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

> i tried to bisect it but it's inconclusive:
> 
>  # bad:  [32beef9c] Merge branch 'perfcounters/core'
>  # bad:  [b6413360] manual merge of x86/platform
>  # bad:  [d9e5f39a] Merge branch 'auto-oprofile-next' into auto-latest
>  # bad:  [cbaff272] Merge branch 'auto-timers-next' into auto-latest
> 
> as the bisection comes up with that merge commit. Perhaps the 
> combination of the x86/platform changes and the clocksource 
> changes triggered it?

That seems to be the case - i just tested a combination merge of 
tip:auto-timers-next and tip:auto-x86-next and the result crashed in 
a similar way too.

Since normal bisection cannot find such breakages, i did a topical 
bisection (merging the finegrained tip:x86/* topics into the timer 
tree gradually and testing each merge).

That way i could exclude: x86/platform, x86/pat, x86/asm, x86/apic, 
x86/percpu, x86/cpu, x86/mm and arrived to x86/tsc - which contains 
a single commit:

  d3b8f88: x86: Make tsc=reliable override boot time stability checks

Reverting that commit from tip:master gives me a non-crashing 
bootup.

	Ingo
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