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

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Message-ID: <20140210192747.GE3416@in.ibm.com>
Date:	Tue, 11 Feb 2014 00:57:47 +0530
From:	Gautham R Shenoy <ego@...ux.vnet.ibm.com>
To:	Gautham R Shenoy <ego@...ux.vnet.ibm.com>
Cc:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	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 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. If so, could
you reword the changelog to reflect this instead of saying "they also
protect the variables ..." ?

--
Thanks and Regards
gautham.

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