On Tue 25-07-17 21:19:52, Andrea Arcangeli wrote: > On Tue, Jul 25, 2017 at 06:04:00PM +0200, Michal Hocko wrote: > > - down_write(&mm->mmap_sem); > > + if (tsk_is_oom_victim(current)) > > + down_write(&mm->mmap_sem); > > free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, USER_PGTABLES_CEILING); > > tlb_finish_mmu(&tlb, 0, -1); > > > > @@ -3012,7 +3014,8 @@ void exit_mmap(struct mm_struct *mm) > > } > > mm->mmap = NULL; > > vm_unacct_memory(nr_accounted); > > - up_write(&mm->mmap_sem); > > + if (tsk_is_oom_victim(current)) > > + up_write(&mm->mmap_sem); > > How is this possibly safe? mark_oom_victim can run while exit_mmap is > running.
I believe it cannot. We always call mark_oom_victim (on !current) with task_lock held and check task->mm != NULL and we call do_exit->mmput after mm is set to NULL under the same lock. -- Michal Hocko SUSE Labs
