linux-kernel - Re: [PATCH 26/51] x86, oprofile, nmi: Fix CPU hotplug callback registration

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Message-ID: <52F9CAAE.4020308@linux.vnet.ibm.com>
Date:	Tue, 11 Feb 2014 12:31:02 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	ego@...ux.vnet.ibm.com
CC:	paulus@...ba.org, oleg@...hat.com, 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,
	linux@....linux.org.uk, linux-kernel@...r.kernel.org,
	Robert Richter <rric@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: Re: [PATCH 26/51] x86, oprofile, nmi: Fix CPU hotplug callback registration

On 02/11/2014 12:57 AM, Gautham R Shenoy wrote:
> On Tue, Feb 11, 2014 at 12:37:37AM +0530, Gautham R Shenoy wrote:
>> Hi,
>>
>> On Thu, Feb 06, 2014 at 03:39:22AM +0530, Srivatsa S. Bhat wrote:
>>> Fix the oprofile code in x86 by using this latter form of callback
>>> registration. But retain the calls to get/put_online_cpus(), since they
>>> also protect the variables 'nmi_enabled' and 'ctr_running'.
>>
>> get/put_online_cpus() protect us against cpu_hotplug_begin/end(). The
>> latter is always nested inside cpu_maps_update_begin/end(), which we
>> are already using here. 
>>
>> So what additional protection are we getting by retaining
>> get/put_online_cpus() ?
> 
> Probably you mean to say that there are other places which access
> 'nmi_enabled' and 'ctr_running' with the cpu-hotplug protection
> provided only by get/put_online_cpus() and you are retaining the calls
> in this patch to be consistent with those other places.

Yep, exactly!

> If so, could
> you reword the changelog to reflect this instead of saying "they also
> protect the variables ..." ?
>

Ok, will do! Thanks a lot!
 
Regards,
Srivatsa S. Bhat

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