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 <rientjes@xxxxxxxxxx>
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.
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.
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