[PATCH 2/2] sched: Try tp catch cpu_power being set to 0

[Tim Gardner]

On 01/20/2011 09:11 AM, Stefan Bader wrote:
> On 01/19/2011 03:20 PM, Andy Whitcroft wrote:
>> On Tue, Jan 18, 2011 at 04:34:23PM +0100, Stefan Bader wrote:
>>> This is an optional change to try catching the culprit which changes
>>> cpu_power to 0 (should never happen) and causes divide by zero crashes
>>> later on in the scheduler code.
>>>
>>> BugLink: http://bugs.launchpad.net/bugs/614853
>>>
>>> Signed-off-by: Stefan Bader<stefan.bader at canonical.com>
>>> ---
>>>   kernel/sched.c |   12 +++++++++++-
>>>   1 files changed, 11 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/kernel/sched.c b/kernel/sched.c
>>> index d4a4b14..7ef70c0 100644
>>> --- a/kernel/sched.c
>>> +++ b/kernel/sched.c
>>> @@ -3713,6 +3713,7 @@ static void update_cpu_power(struct sched_domain *sd, int cpu)
>>>   	unsigned long weight = sd->span_weight;
>>>   	unsigned long power = SCHED_LOAD_SCALE;
>>>   	struct sched_group *sdg = sd->groups;
>>> +	unsigned long scale_rt;
>>>
>>>   	if (sched_feat(ARCH_POWER))
>>>   		power *= arch_scale_freq_power(sd, cpu);
>>> @@ -3730,12 +3731,18 @@ static void update_cpu_power(struct sched_domain *sd, int cpu)
>>>   		power>>= SCHED_LOAD_SHIFT;
>>>   	}
>>>
>>> -	power *= scale_rt_power(cpu);
>>> +	scale_rt = scale_rt_power(cpu);
>>> +	power *= scale_rt;
>>> +
>>>   	power>>= SCHED_LOAD_SHIFT;
>>>
>>>   	if (!power)
>>>   		power = 1;
>>>
>>> +	if (WARN_ON((long) power<= 0))
>>> +		printk(KERN_ERR "cpu_power = %ld; scale_rt = %ld\n",
>>> +			power, scale_rt);
>>> +
>>
>> This is meant to catch when power == 0, but just above power is zapped
>> to 1 if it is 0.  Did we want to catch the 0 ie should this be above the
>> power zapping ?  I guess this is more checking>2^32 ?
>>
>>>   	sdg->cpu_power = power;
>>>   }
>>>
>>> @@ -3759,6 +3766,9 @@ static void update_group_power(struct sched_domain *sd, int cpu)
>>>   	} while (group != child->groups);
>>>
>>>   	sdg->cpu_power = power;
>>> +
>>> +	if (WARN_ON((long) power<= 0))
>>> +		printk(KERN_ERR "cpu_power = %ld\n", power);
>>
>> This is a little odd, I assume its really checking that power is
>> not>2^32 and != 0.
>>
>> Otherwise I suspect the intent is reasonable.  If this has been boot
>> tested I guess it is ok.  Cirtainly 1/2 is a major paper over the bug
>> type fix so something needs to be added to try and catch it.
>>
>> Acked-by: Andy Whitcroft<apw at canonical.com>
>>
>> -apw
>
> Ok, so without changing those I just tried a Lucid ec2 kernel for 32 and 64 bit
> with all the 3 recently posted patches applied and it still boots without any
> complaints. So it seems (even with the questionable sense) it does not cause
> pain to add them.
>
> -Stefan
>

Since this is quite testable:

Acked-by: Tim Gardner <tim.gardner at canonical.com>

-- 
Tim Gardner tim.gardner at canonical.com