use of PREEMPT_ACTIVE ?

use of PREEMPT_ACTIVE ?

[Julien.Soula]

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hello,

the PREEMPT_ACTIVE flag set by preempt_schedule() or during return of
interrupt / exception / syscall. And it's tested in schedule() to
avoid some operations like deactivate_task().

Our purpose is to force deactivation of the task. So we planned to set
task state to TASK_INTERRUPTIBLE value and then to call
schedule(). However the PREEMPT_ACTIVE flag can prevent it.

So what is the significance of the PREEMPT_ACTIVE flag and the test in
schedule() ?

Sincerly, thanks in advance,
-- 
Julien


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Re: use of PREEMPT_ACTIVE ?

[Robert Love]

On Thu, 2004-03-18 at 14:51, Julien.Soula@lifl.fr wrote:

> the PREEMPT_ACTIVE flag set by preempt_schedule() or during return of
> interrupt / exception / syscall. And it's tested in schedule() to
> avoid some operations like deactivate_task().
> 
> Our purpose is to force deactivation of the task. So we planned to set
> task state to TASK_INTERRUPTIBLE value and then to call
> schedule(). However the PREEMPT_ACTIVE flag can prevent it.
> 
> So what is the significance of the PREEMPT_ACTIVE flag and the test in
> schedule() ?

It lets a task be preempted when state != TASK_RUNNING.  By preventing
the task from being deactivated, it can be rescheduled correctly. 
Otherwise, a task that was, say, TASK_INTERRUPTIBLE could be preempted
before it put itself on a wait queue.

Marking the task that is preempted is a simple solution to the race.

If you want to force the deactivation of the task, there is really no
difference.  Set it to TASK_INTERRUPTIBLE, do whatever you need to do,
and call schedule().

PREEMPT_ACTIVE is unrelated to what you want to do.

	Robert Love