Messages in this thread | | | Date | Mon, 26 Mar 2018 11:35:15 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH RT] Defer migrate_enable migration while task state != TASK_RUNNING |
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On Fri, 23 Mar 2018 13:21:31 -0400 joe.korty@concurrent-rt.com wrote:
> My understanding is, in standard Linux and in rt, setting > task state to anything other than TASK_RUNNING in of itself > blocks preemption.
That is clearly false. The only thing that blocks preemption with a CONFIG_PREEMPT kernel is preempt_disable() and local_irq*() disabling.
(Note spin_locks call preempt_disable in non RT).
Otherwise, nothing will stop preemption.
> A preemption is not really needed here > as it is expected that there is a schedule() written in that > will shortly be executed. And if a 'involuntary schedule' > (ie, preemption) were allowed to occur between the task > state set and the schedule(), that would change the task > state back to TASK_RUNNING, which would cause the schedule > to NOP. Thus we risk not having paused long enough here > for the condition we were waiting for to become true.
That is also incorrect. As Julia mentioned, a preemption keeps the state of the task.
-- Steve
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