On Mon 10-07-17 16:55:22, David Rientjes wrote:
> On Mon, 26 Jun 2017, Michal Hocko wrote:
>
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index 3bd5ecd20d4d..253808e716dc 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -2962,6 +2962,11 @@ 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);
> >
> > + /*
> > + * oom reaper might race with exit_mmap so make sure we won't free
> > + * page tables or unmap VMAs under its feet
> > + */
> > + down_write(&mm->mmap_sem);
> > free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, USER_PGTABLES_CEILING);
> > tlb_finish_mmu(&tlb, 0, -1);
> >
> > @@ -2974,7 +2979,9 @@ void exit_mmap(struct mm_struct *mm)
> > nr_accounted += vma_pages(vma);
> > vma = remove_vma(vma);
> > }
> > + mm->mmap = NULL;
> > vm_unacct_memory(nr_accounted);
> > + up_write(&mm->mmap_sem);
> > }
> >
> > /* Insert vm structure into process list sorted by address
> > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > index 0e2c925e7826..5dc0ff22d567 100644
> > --- a/mm/oom_kill.c
> > +++ b/mm/oom_kill.c
> > @@ -472,36 +472,8 @@ static bool __oom_reap_task_mm(struct task_struct
> > *tsk, struct mm_struct *mm)
> > struct vm_area_struct *vma;
> > bool ret = true;
> >
> > - /*
> > - * We have to make sure to not race with the victim exit path
> > - * and cause premature new oom victim selection:
> > - * __oom_reap_task_mm exit_mm
> > - * mmget_not_zero
> > - * mmput
> > - * atomic_dec_and_test
> > - * exit_oom_victim
> > - * [...]
> > - * out_of_memory
> > - * select_bad_process
> > - * # no TIF_MEMDIE task selects new
> > victim
> > - * unmap_page_range # frees some memory
> > - */
> > - mutex_lock(&oom_lock);
> > -
> > - if (!down_read_trylock(&mm->mmap_sem)) {
> > - ret = false;
> > - goto unlock_oom;
> > - }
> > -
> > - /*
> > - * increase mm_users only after we know we will reap something so
> > - * that the mmput_async is called only when we have reaped something
> > - * and delayed __mmput doesn't matter that much
> > - */
> > - if (!mmget_not_zero(mm)) {
> > - up_read(&mm->mmap_sem);
> > - goto unlock_oom;
> > - }
> > + if (!down_read_trylock(&mm->mmap_sem))
> > + return false;
>
> I think this should return true if mm->mmap == NULL here.
This?
---
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 5dc0ff22d567..e155d1d8064f 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -470,11 +470,14 @@ static bool __oom_reap_task_mm(struct task_struct *tsk,
struct mm_struct *mm)
{
struct mmu_gather tlb;
struct vm_area_struct *vma;
- bool ret = true;
if (!down_read_trylock(&mm->mmap_sem))
return false;
+ /* There is nothing to reap so bail out without signs in the log */
+ if (!mm->mmap)
+ goto unlock;
+
/*
* Tell all users of get_user/copy_from_user etc... that the content
* is no longer stable. No barriers really needed because unmapping
@@ -508,9 +511,10 @@ static bool __oom_reap_task_mm(struct task_struct *tsk,
struct mm_struct *mm)
K(get_mm_counter(mm, MM_ANONPAGES)),
K(get_mm_counter(mm, MM_FILEPAGES)),
K(get_mm_counter(mm, MM_SHMEMPAGES)));
+unlock:
up_read(&mm->mmap_sem);
- return ret;
+ return true;
}
#define MAX_OOM_REAP_RETRIES 10
--
Michal Hocko
SUSE Labs
