linux-kernel - Re: [PATCH] cpuidle: Fix panic in CPU off-lining with no idle driver

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Message-ID: <4F7B2102.3080006@hp.com>
Date:	Tue, 03 Apr 2012 10:10:42 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
CC:	len.brown@...el.com, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Boris Ostrovsky <boris.ostrovsky@....com>, lenb@...nel.org,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	amit.kucheria@...aro.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH] cpuidle: Fix panic in CPU off-lining with no idle driver

On 4/3/2012 8:08 AM, Srivatsa S. Bhat wrote:
> On 04/01/2012 09:07 AM, Toshi Kani wrote:
>
>> Fix a NULL pointer dereference panic in cpuidle_play_dead() during
>> CPU off-lining when no cpuidle driver is registered.  A cpuidle
>> driver may be registered at boot-time based on CPU type.  This patch
>> allows an off-lined CPU to enter HLT-based idle in this condition.
>>
>> Signed-off-by: Toshi Kani<toshi.kani@...com>
>> Cc: Boris Ostrovsky<boris.ostrovsky@....com>
>> ---
>>   drivers/cpuidle/cpuidle.c |    5 ++++-
>>   1 files changed, 4 insertions(+), 1 deletions(-)
>>
>> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
>> index 87411ce..2f0083a 100644
>> --- a/drivers/cpuidle/cpuidle.c
>> +++ b/drivers/cpuidle/cpuidle.c
>> @@ -74,7 +74,7 @@ static cpuidle_enter_t cpuidle_enter_ops;
>>   /**
>>    * cpuidle_play_dead - cpu off-lining
>>    *
>> - * Only returns in case of an error
>> + * Returns in case of an error or no driver
>>    */
>>   int cpuidle_play_dead(void)
>>   {
>> @@ -83,6 +83,9 @@ int cpuidle_play_dead(void)
>>   	int i, dead_state = -1;
>>   	int power_usage = -1;
>>
>> +	if (!drv)
>> +		return -ENODEV;
>> +
>>   	/* Find lowest-power state that supports long-term idle */
>>   	for (i = CPUIDLE_DRIVER_STATE_START; i<  drv->state_count; i++) {
>>   		struct cpuidle_state *s =&drv->states[i];
>
>
> Reviewed-by: Srivatsa S. Bhat<srivatsa.bhat@...ux.vnet.ibm.com>
> Tested-by: Srivatsa S. Bhat<srivatsa.bhat@...ux.vnet.ibm.com>
>
>
> [The machine I tested on did support mwait. So, to disable mwait and ensure
> that no idle driver is registered, I applied my fix for "idle=" parameters
> (https://lkml.org/lkml/2012/4/3/158) and then passed idle=halt in the kernel
> command line. Then the machine crashed during CPU offline. Then I tried your
> patch and it fixed the issue.]

Great!  Thanks a lot Srivatsa for reviewing and testing!
-Toshi

> Regards,
> Srivatsa S. Bhat
> IBM Linux Technology Center
>

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