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
On Thu, 2004-03-18 at 14:51, [email protected] 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