linux-kernel - Re: [PATCH] cpuidle: coupled: fix sleeping while atomic in cpu notifier

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Date:	Wed, 01 Aug 2012 11:29:50 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Colin Cross <ccross@...roid.com>
CC:	Len Brown <lenb@...nel.org>, Len Brown <len.brown@...el.com>,
	Kevin Hilman <khilman@...com>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-kernel@...r.kernel.org,
	Linux PM mailing list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] cpuidle: coupled: fix sleeping while atomic in cpu notifier

On 07/31/2012 11:57 PM, Colin Cross wrote:
> On Tue, Jul 31, 2012 at 8:43 AM, Srivatsa S. Bhat
> <srivatsa.bhat@...ux.vnet.ibm.com> wrote:
>> On 07/26/2012 02:50 AM, Colin Cross wrote:
>>> The cpu hotplug notifier gets called in both atomic and non-atomic
>>> contexts, it is not always safe to lock a mutex.  Filter out all events
>>> except the six necessary ones, which are all sleepable, before taking
>>> the mutex.
>>>
>>> Signed-off-by: Colin Cross <ccross@...roid.com>
>>> ---
>>>  drivers/cpuidle/coupled.c |   12 ++++++++++++
>>>  1 files changed, 12 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/drivers/cpuidle/coupled.c b/drivers/cpuidle/coupled.c
>>> index 2c9bf26..c24dda0 100644
>>> --- a/drivers/cpuidle/coupled.c
>>> +++ b/drivers/cpuidle/coupled.c
>>> @@ -678,6 +678,18 @@ static int cpuidle_coupled_cpu_notify(struct notifier_block *nb,
>>>       int cpu = (unsigned long)hcpu;
>>>       struct cpuidle_device *dev;
>>>
>>> +     switch (action & ~CPU_TASKS_FROZEN) {
>>> +     case CPU_UP_PREPARE:
>>> +     case CPU_DOWN_PREPARE:
>>> +     case CPU_ONLINE:
>>> +     case CPU_DEAD:
>>> +     case CPU_UP_CANCELED:
>>> +     case CPU_DOWN_FAILED:
>>> +             break;
>>> +     default:
>>> +             return NOTIFY_OK;
>>> +     }
>>> +
>>
>> Instead, wouldn't it be better to have case statements for the
>> 2 cases that imply atomic context and return immediately?
>>
>> Something like:
>>         switch (action & ~CPU_TASKS_FROZEN) {
>>         case CPU_STARTING:
>>         case CPU_DYING:
>>                 return NOTIFY_OK;
>>         }
> 
> No, because then it would need updating whenever a new notification
> event was added.
> 

Hmm.. Fair enough.

Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>

Regards,
Srivatsa S. Bhat

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