On Fri 08-12-17 01:26:46, David Rientjes wrote:
> On Thu, 7 Dec 2017, David Rientjes wrote:
>
> > I'm backporting and testing the following patch against Linus's tree. To
> > clarify an earlier point, we don't actually have any change from upstream
> > code that allows for free_pgtables() before the
> > set_bit(MMF_OOM_SKIP);down_write();up_write() cycle.
> >
> > diff --git a/include/linux/oom.h b/include/linux/oom.h
> > --- a/include/linux/oom.h
> > +++ b/include/linux/oom.h
> > @@ -66,6 +66,15 @@ static inline bool tsk_is_oom_victim(struct task_struct
> > * tsk)
> > return tsk->signal->oom_mm;
> > }
> >
> > +/*
> > + * Use this helper if tsk->mm != mm and the victim mm needs a special
> > + * handling. This is guaranteed to stay true after once set.
> > + */
> > +static inline bool mm_is_oom_victim(struct mm_struct *mm)
> > +{
> > + return test_bit(MMF_OOM_VICTIM, &mm->flags);
> > +}
> > +
> > /*
> > * Checks whether a page fault on the given mm is still reliable.
> > * This is no longer true if the oom reaper started to reap the
> > diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h
> > --- a/include/linux/sched/coredump.h
> > +++ b/include/linux/sched/coredump.h
> > @@ -71,6 +71,7 @@ static inline int get_dumpable(struct mm_struct *mm)
> > #define MMF_HUGE_ZERO_PAGE 23 /* mm has ever used the global huge
> > zero page */
> > #define MMF_DISABLE_THP 24 /* disable THP for all VMAs */
> > #define MMF_DISABLE_THP_MASK (1 << MMF_DISABLE_THP)
> > +#define MMF_OOM_VICTIM 25 /* mm is the oom victim */
> >
> > #define MMF_INIT_MASK (MMF_DUMPABLE_MASK |
> > MMF_DUMP_FILTER_MASK |\
> > MMF_DISABLE_THP_MASK)
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -3019,20 +3019,20 @@ void exit_mmap(struct mm_struct *mm)
> > /* Use -1 here to ensure all VMAs in the mm are unmapped */
> > unmap_vmas(&tlb, vma, 0, -1);
> >
> > - set_bit(MMF_OOM_SKIP, &mm->flags);
> > - if (unlikely(tsk_is_oom_victim(current))) {
> > + if (unlikely(mm_is_oom_victim(mm))) {
> > /*
> > * Wait for oom_reap_task() to stop working on this
> > * mm. Because MMF_OOM_SKIP is already set before
> > * calling down_read(), oom_reap_task() will not run
> > * on this "mm" post up_write().
> > *
> > - * tsk_is_oom_victim() cannot be set from under us
> > + * mm_is_oom_victim() cannot be set from under us
> > * either because current->mm is already set to NULL
> > * under task_lock before calling mmput and oom_mm is
> > * set not NULL by the OOM killer only if current->mm
> > * is found not NULL while holding the task_lock.
> > */
> > + set_bit(MMF_OOM_SKIP, &mm->flags);
> > down_write(&mm->mmap_sem);
> > up_write(&mm->mmap_sem);
> > }
> > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > --- a/mm/oom_kill.c
> > +++ b/mm/oom_kill.c
> > @@ -683,8 +683,10 @@ static void mark_oom_victim(struct task_struct *tsk)
> > return;
> >
> > /* oom_mm is bound to the signal struct life time. */
> > - if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm))
> > + if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm)) {
> > mmgrab(tsk->signal->oom_mm);
> > + set_bit(MMF_OOM_VICTIM, &mm->flags);
> > + }
> >
> > /*
> > * Make sure that the task is woken up from uninterruptible sleep
> >
>
> This passes all functional testing that I have and I can create a
> synthetic testcase that can trigger at least MMF_OOM_VICTIM getting set
> while oom_reaper is still working on an mm that this prevents, so feel
> free to add an
>
> Acked-by: David Rientjes <rient...@google.com>
>
> with a variant of your previous changelogs. Thanks!
>
> I think it would appropriate to cc stable for 4.14 and add a
>
> Fixes: 212925802454 ("mm: oom: let oom_reap_task and exit_mmap run
> concurrently")
>
> if nobody disagrees, which I think you may have already done on a previous
> iteration.
Thanks for your testing! I will repost the patch later today.
> We can still discuss if there are any VM_LOCKED subtleties in the this
> thread, but I have no evidence that it is responsible for any issues.
Yes this is worth a separate discussion.
--
Michal Hocko
SUSE Labs
