scheduling - more doubts

[pmkernel@gmail.com (piyush moghe)]

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@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
>
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