linux-kernel - Re: [PATCH 3/4] cpu: export cpu hotplug disable/enable functions as global functions

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Date:	Wed, 08 Aug 2012 11:43:22 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Kumar Gala <galak@...nel.crashing.org>
CC:	rjw@...k.pl, Zhao Chenhui <chenhui.zhao@...escale.com>,
	"linuxppc-dev@...ts.ozlabs.org list" <linuxppc-dev@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org list" <linux-kernel@...r.kernel.org>,
	Li Yang <leoli@...escale.com>
Subject: Re: [PATCH 3/4] cpu: export cpu hotplug disable/enable functions
 as global functions

On 08/07/2012 11:21 PM, Kumar Gala wrote:
> 
> On Aug 7, 2012, at 3:43 AM, Zhao Chenhui wrote:
> 
>> The cpufreq driver of mpc85xx will disable/enable cpu hotplug temporarily.
>> Therefore, the related functions should be exported.
>>
>> Signed-off-by: Zhao Chenhui <chenhui.zhao@...escale.com>
>> ---
>> include/linux/cpu.h |    4 ++++
>> 1 files changed, 4 insertions(+), 0 deletions(-)
> 
> Rafael, Srivatsa,
> 
> Wanted to get your ack on export these functions for direct calling by arch code.
>

Why not just use get_online_cpus()/put_online_cpus()?

In the case of suspend/resume/hibernation, we had introduced these CPU hotplug disable
functions because we would end up doing CPU hotplug ourselves, further down the path.
So if we did a get_online_cpus(), we would end up deadlocking ourselves. Whereas, the
patch 4/4 looks like a straightforward case of wanting to simply disable CPU hotplug..
I don't see where you are doing CPU hotplug yourself in the path. So IMO, just
get/put_online_cpus() should do.

Regards,
Srivatsa S. Bhat

> 
>>
>> diff --git a/include/linux/cpu.h b/include/linux/cpu.h
>> index ce7a074..df8f73d 100644
>> --- a/include/linux/cpu.h
>> +++ b/include/linux/cpu.h
>> @@ -146,6 +146,8 @@ void notify_cpu_starting(unsigned int cpu);
>> extern void cpu_maps_update_begin(void);
>> extern void cpu_maps_update_done(void);
>>
>> +extern void cpu_hotplug_disable_before_freeze(void);
>> +extern void cpu_hotplug_enable_after_thaw(void);
>> #else	/* CONFIG_SMP */
>>
>> #define cpu_notifier(fn, pri)	do { (void)(fn); } while (0)
>> @@ -167,6 +169,8 @@ static inline void cpu_maps_update_done(void)
>> {
>> }
>>
>> +static inline void cpu_hotplug_disable_before_freeze(void)	{}
>> +static inline void cpu_hotplug_enable_after_thaw(void)	{}
>> #endif /* CONFIG_SMP */
>> extern struct bus_type cpu_subsys;
>>
>> -- 
>> 1.6.4.1
>>
> 

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