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

john stultz
2009-09-08T21:43:16Z

On Thu, 2009-09-03 at 20:58 +0200, Ingo Molnar wrote:
> * Ingo Molnar <mingo@elte.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.

Huh. Does dropping the last chunk of the patch make the issue go away?

I'm suspecting fixing the bug Thomas noticed in the tsc_unstable
assignment (we set tsc_unstable before calling mark_tsc_unstable,
causing the TSC rating to not change) that I included in this patch is
colliding with the clocksource rework from Martin.

Although I'm not sure I see that in the backtrace, so I'm likely wrong.
Hrmm..

-john