Messages in this thread |  | | Date | Fri, 25 Sep 2020 10:43:39 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 8/9] sched: Fix migrate_disable() vs set_cpus_allowed_ptr() |
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On Thu, Sep 24, 2020 at 08:59:33PM +0100, Valentin Schneider wrote:
> > + if (task_running(rq, p) || p->state == TASK_WAKING) { > > + > > + task_rq_unlock(rq, p, rf); > > + stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg); > > + > > Shouldn't we check for is_migrate_disabled(p) before doing any of that? > migration_cpu_stop() does check for it, is there something that prevents us > from acting on it earlier than that?
Since migrate_disable() / ->migration_disabled is only touched from the current task, you can only reliably read it from the same CPU.
Hence I only look at it when the stop task has pinned the task, because at that point I know it's stable.
Doing it earlier gives races, races give me head-aches. This is a slow path, I don't care about performance.
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