Re: [RFC PATCH 03/13] sched: Core-wide rq->lock

Vineeth Remanan Pillai
2020-04-14T21:35:29Z

> Aside from the fact that it's probably much saner to write this as:
>
> rq->core_enabled = static_key_enabled(&__sched_core_enabled);
>
> I'm fairly sure I didn't write this part. And while I do somewhat see
> the point of disabling core scheduling for a core that has only a single
> thread on, I wonder why we care.
>
I think this change was to fix some crashes which happened due to
uninitialized rq->core if a sibling was offline during boot and is
onlined after coresched was enabled.

https://lwn.net/ml/linux-kernel/20190424111913.1386-1-vpillai@digitalocean.com/

I tried to fix it by initializing coresched members during a cpu online
and tearing it down on a cpu offline. This was back in v3 and do not
remember the exact details. I shall revisit this and see if there is a
better way to fix the race condition above.

Thanks,
Vineeth