linux-kernel - Re: [PATCH 19/51] x86, therm_throt.c: Fix CPU hotplug callback registration

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Date:	Mon, 10 Feb 2014 23:34:23 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	paulus@...ba.org, rusty@...tcorp.com.au, peterz@...radead.org,
	tglx@...utronix.de, akpm@...ux-foundation.org, mingo@...nel.org,
	paulmck@...ux.vnet.ibm.com, tj@...nel.org, walken@...gle.com,
	ego@...ux.vnet.ibm.com, linux@....linux.org.uk,
	linux-kernel@...r.kernel.org, Tony Luck <tony.luck@...el.com>,
	Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-edac@...r.kernel.org
Subject: Re: [PATCH 19/51] x86, therm_throt.c: Fix CPU hotplug callback registration

On 02/10/2014 10:59 PM, Srivatsa S. Bhat wrote:
> On 02/10/2014 09:23 PM, Oleg Nesterov wrote:
>> On 02/06, Srivatsa S. Bhat wrote:
>>>
>>> --- a/arch/x86/kernel/cpu/mcheck/therm_throt.c
>>> +++ b/arch/x86/kernel/cpu/mcheck/therm_throt.c
>>> @@ -319,7 +319,7 @@ static __init int thermal_throttle_init_device(void)
>>>  	if (!atomic_read(&therm_throt_en))
>>>  		return 0;
>>>
>>> -	register_hotcpu_notifier(&thermal_throttle_cpu_notifier);
>>> +	cpu_maps_update_begin();
>>>
>>>  #ifdef CONFIG_HOTPLUG_CPU
>>>  	mutex_lock(&therm_cpu_lock);
>>> @@ -333,6 +333,9 @@ static __init int thermal_throttle_init_device(void)
>>>  	mutex_unlock(&therm_cpu_lock);
>>>  #endif
>>>
>>> +	__register_hotcpu_notifier(&thermal_throttle_cpu_notifier);
>>> +	cpu_maps_update_done();
>>
>>
>> Off-topic, but it seems that after this change therm_cpu_lock can die.
>> Of course this needs another patch (if I am right).
>>
> 
> I'm not sure I understood that clearly. Can you please explain?
> 
> I'm guessing that you are referring to some problem with the #ifdef
> CONFIG_HOTPLUG_CPU around mutex_lock/unlock(&therm_cpu_lock) ?
>

Oh, nevermind, now I see it. Basically you are suggesting that therm_cpu_lock
is useless after this patch and hence can be removed entirely. Yep, that
makes sense. (I hadn't noticed it earlier). I'll incorporate that change
in a separate patch in my v2 of the patchset. Thank you!
 
Regards,
Srivatsa S. Bhat

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