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

From: Andrew Morton <akpm@osdl.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@timesys.com>,
	Alan Stern <stern@rowland.harvard.edu>,
	LKML <linux-kernel@vger.kernel.org>,
	Linus Torvalds <torvalds@osdl.org>,
	john stultz <johnstul@us.ibm.com>,
	David Miller <davem@davemloft.net>,
	Arjan van de Ven <arjan@infradead.org>, Andi Kleen <ak@suse.de>
Subject: Re: [patch] cpufreq: mark cpufreq_tsc() as core_initcall_sync
Date: Thu, 16 Nov 2006 13:20:58 -0800	[thread overview]
Message-ID: <20061116132058.4c541bde.akpm@osdl.org> (raw)
In-Reply-To: <20061116201531.GA31469@elte.hu>

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

> 
> * Thomas Gleixner <tglx@timesys.com> 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@elte.hu>
> 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@elte.hu>
> 
> --- 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.