Re: [PATCH] mm,page_alloc: PF_WQ_WORKER threads must sleep at should_reclaim_retry().

[Tetsuo Handa]

Michal Hocko wrote:
> > I assert that we should fix af5679fbc669f31f.
> 
> If you can come up with reasonable patch which doesn't complicate the
> code and it is a clear win for both this particular workload as well as
> others then why not.

Why can't we do "at least MMF_OOM_SKIP should be set under the lock to
prevent from races" ?

diff --git a/mm/mmap.c b/mm/mmap.c
index 5f2b2b1..e096bb8 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3065,7 +3065,9 @@ void exit_mmap(struct mm_struct *mm)
                 */
                (void)__oom_reap_task_mm(mm);
 
+               mutex_lock(&oom_lock);
                set_bit(MMF_OOM_SKIP, &mm->flags);
+               mutex_unlock(&oom_lock);
                down_write(&mm->mmap_sem);
                up_write(&mm->mmap_sem);
        }
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index f10aa53..b2a94c1 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -606,7 +606,9 @@ static void oom_reap_task(struct task_struct *tsk)
         * Hide this mm from OOM killer because it has been either reaped or
         * somebody can't call up_write(mmap_sem).
         */
+       mutex_lock(&oom_lock);
        set_bit(MMF_OOM_SKIP, &mm->flags);
+       mutex_unlock(&oom_lock);                
 
        /* Drop a reference taken by wake_oom_reaper */
        put_task_struct(tsk);