Re: [PATCH 1/1] rcu/tree: Drop the lock before entering to page allocator

Uladzislau Rezki
2020-07-16T14:47:34Z

On Thu, Jul 16, 2020 at 04:25:37PM +0200, Sebastian Andrzej Siewior wrote:
> On 2020-07-16 11:19:13 [+0200], Uladzislau Rezki wrote:
> > Sebastian, could you please confirm that if that patch that is in
> > question fixes it?
> >
> > It would be appreciated!
>
> So that preempt disable should in terms any warnings. However I don't
> think that it is strictly needed and from scheduling point of view you
> forbid a CPU migration which might be good otherwise.
>
Please elaborate your point regarding "i do not think it is strictly needed".

Actually i can rework the patch to remove even such preempt_enable/disable
to stay on the same CPU, but i do not see the point of doing it.

Do you see the point?

As for scheduling point of view. Well, there are many places when there
is a demand in memory or pages from atomic context. Also, getting a page
is not considered as a hot path in the kfree_rcu().

>
> Also if interrupts and everything is enabled then someone else might
> invoke kfree_rcu() from BH context for instance.
>
And what? What is a problem here, please elaborate if you see any
issues.

--
Vlad Rezki