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Date:	Fri, 14 Feb 2014 23:33:14 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
CC:	"paulus@...ba.org" <paulus@...ba.org>, oleg@...hat.com,
	Ingo Molnar <mingo@...nel.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Tejun Heo <tj@...nel.org>,
	Michel Lespinasse <walken@...gle.com>, ego@...ux.vnet.ibm.com,
	Russell King <linux@....linux.org.uk>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux-Arch <linux-arch@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: [PATCH v2 27/52] x86, pci, amd-bus: Fix CPU hotplug callback
 registration

On 02/14/2014 11:05 PM, Bjorn Helgaas wrote:
> On Fri, Feb 14, 2014 at 12:55 AM, Srivatsa S. Bhat
> <srivatsa.bhat@...ux.vnet.ibm.com> wrote:
>> Subsystems that want to register CPU hotplug callbacks, as well as perform
>> initialization for the CPUs that are already online, often do it as shown
>> below:
>>
>>         get_online_cpus();
>>
>>         for_each_online_cpu(cpu)
>>                 init_cpu(cpu);
>>
>>         register_cpu_notifier(&foobar_cpu_notifier);
>>
>>         put_online_cpus();
>>
>> This is wrong, since it is prone to ABBA deadlocks involving the
>> cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently
>> with CPU hotplug operations).
>>
>> Instead, the correct and race-free way of performing the callback
>> registration is:
>>
>>         cpu_notifier_register_begin();
>>
>>         for_each_online_cpu(cpu)
>>                 init_cpu(cpu);
>>
>>         /* Note the use of the double underscored version of the API */
>>         __register_cpu_notifier(&foobar_cpu_notifier);
>>
>>         cpu_notifier_register_done();
>>
>>
>> Fix the amd-bus code in x86 by using this latter form of callback
>> registration.
>>
>> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>> Cc: Ingo Molnar <mingo@...nel.org>
>> Cc: "H. Peter Anvin" <hpa@...or.com>
>> Cc: x86@...nel.org
>> Cc: linux-pci@...r.kernel.org
>> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
> 
> This looks fine to me.
> 
> Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>
> 
> I think it makes sense for you to merge it along with all your other
> similar changes.  I don't foresee any conflicts with things in my PCI
> tree.
> 

Great! Thank you!

Regards,
Srivatsa S. Bhat

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