scheduling - more doubts

[Sudheer]

On Mon, Mar 7, 2011 at 9:42 AM, piyush moghe <pmkernel at gmail.com> wrote:
> Hi Sudheer,
>     If you see there is a schedule_timeout function called with some timeout
> so if you receive any signal ( handled by apm_event_handler )  before the
> timeout value it will be woken up and if it receives no signal before
> timeout value than scheduler will move this to RUNNABLE state again.
> Regards,
> Piyush
>
> On Thu, Mar 3, 2011 at 5:20 PM, <sudheer.divakaran at wipro.com> wrote:
>>
>> Hi,
>>
>> I had asked a similar question before, but I've some doubts regarding the
>> correctness of the following code. Please see the following code snippet
>> from the file linux-2.6.37/arch/x86/kernel/apm_32.c. This is the core
>> function of apm thread.
>>
>>
>> Question:
>> Suppose the apm thread has just completed execution of the line 1442 and
>> the scheduling happens for some reason, AFAIK, since the apm thread's state
>> has been set to TASK_INTERRUPTIBLE, it will be removed from the run-queue.
>> So there is a chance for the apm thread to remain suspended indefinitely as
>> nobody is there to wakeup the apm thread, correct?
>>
>> I'm asking this because the same function has been given as an example in
>> the following link and would like to confirm the accuracy of the example.
>>
>> http://www.linuxjournal.com/node/8144/print
>>
>>
>>
>> 1437 static void apm_mainloop(void)
>> 1438 {
>> 1439     DECLARE_WAITQUEUE(wait, current);
>> 1440
>> 1441     add_wait_queue(&apm_waitqueue, &wait);
>> 1442     set_current_state(TASK_INTERRUPTIBLE);
>> 1443     for (;;) {
>> 1444         schedule_timeout(APM_CHECK_TIMEOUT);
>> 1445         if (kthread_should_stop())
>> 1446             break;
>> 1447         /*
>> 1448          * Ok, check all events, check for idle (and mark us sleeping
>> 1449          * so as not to count towards the load average)..
>> 1450          */
>> 1451         set_current_state(TASK_INTERRUPTIBLE);
>> 1452         apm_event_handler();
>> 1453     }
>> 1454     remove_wait_queue(&apm_waitqueue, &wait);
>> 1455 }
>>
>>
>> --
>> Thanks,
>> Sudheer
>>


Hi,
My question was the apm thread getting scheduled out of run queue at
apm_32.c line no 1443.
i.e., for(;;), just after executing the line 1442, i.e.,

set_current_state(TASK_INTERRUPTIBLE);

In this case, AFAIK,  schedule_timeout(APM_CHECK_TIMEOUT) will not be
executed as the apm thread will not be returned to the run queue.
CMIIW.

-- 
Thanks
Sudheer