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

[Suren Baghdasaryan]

On Thu, Nov 11, 2021 at 1:20 AM Michal Hocko <mhocko@xxxxxxxx> wrote:
>
> On Wed 10-11-21 17:49:37, Suren Baghdasaryan wrote:
> > On Tue, Nov 9, 2021 at 1:10 PM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote:
> > >
> > > On Tue, Nov 9, 2021 at 12:10 PM Michal Hocko <mhocko@xxxxxxxx> 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.

You are right, it will run concurrently with another
__oom_reap_task_mm in the exit_mmap. But I thought we wanted to get
rid of that call to __oom_reap_task_mm in exit_mmap or did I
misunderstand?

>
> --
> Michal Hocko
> SUSE Labs