Re: [tip:sched/core] cpu: Remove incorrect BUG_ON

Oleg Nesterov
2010-11-23T15:15:08Z

On 11/23, Peter Zijlstra wrote:
>
> Ah,. uhm,. you mean, not do anything at all?
>
> Dunno, really, let me try and read the code there.

Thanks. This is very minor of course, but it would be nice to
undestand the reason. To me it looks unneeded, but I don't trust
myself. (snippets from my previous email below).

With or without this change, even if we know that rq->idle is running
we can't know if it (say) already started play_dead_common() or not.

We are going to call __cpu_die(), afaics it should do the necessary
synchronization in any case.

For example, native_cpu_die() waits for cpu_state == CPU_DEAD in a
loop. Of course it should work in practice (it also does msleep),
but in theory there is no guarantee.

So. Can't we just remove this wait-loop? We know that rq->idle
will be scheduled "soon", I don't understand why it is necessary
to ensure that context_switch() has already happened.

Oleg.