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

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Date:	Tue, 31 Jul 2012 11:27:27 -0700
From:	Colin Cross <ccross@...roid.com>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.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 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.
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