Re: [patch] cpufreq: mark cpufreq_tsc() as core_initcall_sync

[Andrew Morton]

On Thu, 16 Nov 2006 21:15:32 +0100
Ingo Molnar <mingo@xxxxxxx> wrote:

> 
> * Thomas Gleixner <tglx@xxxxxxxxxxx> wrote:
> 
> > [PATCH] cpufreq: make the transition_notifier chain use SRCU
> > (b4dfdbb3c707474a2254c5b4d7e62be31a4b7da9)
> > 
> > breaks cpu frequency notification users, which register the callback 
> > on core_init level. Interestingly enough the registration survives the 
> > uninitialized head, but the registered user is lost by:
> 
> i have hit this bug in -rt (it caused a lockup) and have fixed it - 
> forgot to send it upstream. Find the patch below.
> 
> 	Ingo
> 
> ---------------->
> From: Ingo Molnar <mingo@xxxxxxx>
> Subject: [patch] cpufreq: mark cpufreq_tsc() as core_initcall_sync
> 
> init_cpufreq_transition_notifier_list() should execute first, which is a 
> core_initcall, so mark cpufreq_tsc() core_initcall_sync.

That's not a terribly useful changelog.  What bug is being fixed.  What
does "first" mean?

> Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
> 
> --- linux.orig/arch/x86_64/kernel/tsc.c
> +++ linux/arch/x86_64/kernel/tsc.c
> @@ -138,7 +138,11 @@ static int __init cpufreq_tsc(void)
>  	return 0;
>  }
>  
> -core_initcall(cpufreq_tsc);
> +/*
> + * init_cpufreq_transition_notifier_list() should execute first,
> + * which is a core_initcall, so mark this one core_initcall_sync:
> + */
> +core_initcall_sync(cpufreq_tsc);

Would prefer that we not use the _sync levels.  They're there as a
synchronisation for MULTITHREAD_PROBE and might disappear at any time.

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