Re: [PATCH 1/1] mm: prevent a race between process_mrelease and exit_mmap

Michal Hocko
2021-11-11T09:20:44Z

On Wed 10-11-21 17:49:37, Suren Baghdasaryan wrote:
> On Tue, Nov 9, 2021 at 1:10 PM Suren Baghdasaryan <surenb@google.com> wrote:
> >
> > On Tue, Nov 9, 2021 at 12:10 PM Michal Hocko <mhocko@suse.com> wrote:
[...]
> > > Yes, those can run concurrently. One thing I completely forgot about is
> > > 27ae357fa82b ("mm, oom: fix concurrent munlock and oom reaper unmap, v3")
> > > which is about interaction with the munlock.
>
> Agrh! This interaction with the munlock you mentioned requires us to
> take mmap_write_lock before munlock_vma_pages_all and that prevents
> __oom_reap_task_mm from running concurrently with unmap_vmas. The
> reapers would not be as effective as they are now after such a change
> :(

__oom_reap_task_mm will not run concurrently with unmap_vmas even
with the current code. The mmap_sem barrier right before munlock code
prevents that.

--
Michal Hocko
SUSE Labs