Messages in this thread | | | Subject | Re: use of PREEMPT_ACTIVE ? | From | Robert Love <> | Date | Thu, 18 Mar 2004 15:06:13 -0500 |
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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
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