Re: [RFC PATCH 1/2] Fix: sched/membarrier: p->mm->membarrier_state racy load

[Mathieu Desnoyers]

----- On Sep 4, 2019, at 12:11 PM, Oleg Nesterov oleg@xxxxxxxxxx wrote:

> with or without these changes...
> 
> Why do membarrier_register_*_expedited() check get_nr_threads() == 1?
> This makes no sense to me, atomic_read(mm_users) == 1 should be enough.
> 
> 
> And I am not sure I understand membarrier_mm_sync_core_before_usermode().
> OK, membarrier_private_expedited() can race with user -> kernel -> user
> transition, but we do not care unless both user's above have the same mm?
> Shouldn't membarrier_mm_sync_core_before_usermode() do
> 
>	if (current->mm != mm)
>		return;
> 
> at the start to make it more clear and avoid sync_core_before_usermode()
> if possible?

I think I missed replying to your email. Indeed, you are right, I've added
2 cleanup patches taking care of this in my latest round.

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com