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

Oleg Nesterov
2019-09-04T11:11:35Z

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?

Oleg.