Re: [BUG] TASK_DEAD task is able to be woken up in special condition

KOSAKI Motohiro
2012-01-24T18:01:07Z

On 1/24/2012 5:23 AM, Peter Zijlstra wrote:
> On Wed, 2011-12-28 at 16:07 -0500, KOSAKI Motohiro wrote:
>> I looked at scheduler code today briefly. now I'm afraid following code
>> have similar race.
>>
>>
>> if (task_contributes_to_load(p))
>> rq->nr_uninterruptible--;
>>
>>
>>
>> Can't following schenario be happen?
>>
>>
>> CPU0 CPU1
>> --------------------------------------------------------
>> deactivate_task()
>> task->state = TASK_UNINTERRUPTIBLE;
>> activate_task()
>> rq->nr_uninterruptible--;
>>
>> schedule()
>> deactivate_task()
>> rq->nr_uninterruptible++;
>>
>> Totally, nr_uninterruptible wasn't incremented.
>>
>>
>> I'm still not sure. I need to read more sched code.
>
> You shouldn't ever set another tasks ->state.

I'm sorry. I haven't catch your point. I think following step is
valid kernel code. Do you disagree?

>> task->state = TASK_UNINTERRUPTIBLE;
>> schedule()