On Tue 30-10-18 21:02:40, Tetsuo Handa wrote: > On 2018/10/30 20:39, Michal Hocko wrote: > > On Tue 30-10-18 18:47:43, Tetsuo Handa wrote: > >> On 2018/10/30 15:31, Michal Hocko wrote: > >>> On Tue 30-10-18 13:45:22, Tetsuo Handa wrote: > >>>> Michal Hocko wrote: > >>>>> @@ -3156,6 +3166,13 @@ void exit_mmap(struct mm_struct *mm) > >>>>> vma = remove_vma(vma); > >>>>> } > >>>>> vm_unacct_memory(nr_accounted); > >>>>> + > >>>>> + /* > >>>>> + * Now that the full address space is torn down, make sure the > >>>>> + * OOM killer skips over this task > >>>>> + */ > >>>>> + if (oom) > >>>>> + set_bit(MMF_OOM_SKIP, &mm->flags); > >>>>> } > >>>>> > >>>>> /* Insert vm structure into process list sorted by address > >>>> > >>>> I don't like setting MMF_OOF_SKIP after remove_vma() loop. 50 users might > >>>> call vma->vm_ops->close() from remove_vma(). Some of them are doing fs > >>>> writeback, some of them might be doing GFP_KERNEL allocation from > >>>> vma->vm_ops->open() with a lock also held by vma->vm_ops->close(). > >>>> > >>>> I don't think that waiting for completion of remove_vma() loop is safe. > >>> > >>> What do you mean by 'safe' here? > >>> > >> > >> safe = "Does not cause OOM lockup." > >> > >> remove_vma() is allowed to sleep, and some users might depend on memory > >> allocation when the OOM killer is waiting for remove_vma() to complete. > > > > But MMF_OOF_SKIP is set after we are done with remove_vma. In fact it is > > the very last thing in exit_mmap. So I do not follow what you mean. > > > > So what? Think the worst case. Quite obvious bug here. I misunderstood your concern. oom_reaper would back off without MMF_OOF_SKIP as well. You are right we cannot assume anything about close callbacks so MMF_OOM_SKIP has to come before that. I will move it behind the pagetable freeing. -- Michal Hocko SUSE Labs
