Re: WARNING in try_charge

Tetsuo Handa
2018-08-07T10:19:13Z

On 2018/08/07 6:50, Tetsuo Handa wrote:
> list_for_each_entry_safe(p, tmp, &oom_victim_list, oom_victim_list) {
> struct mm_struct *mm = p->signal->oom_mm;
>
> if (oom_unkillable_task(p, oc->memcg, oc->nodemask))
> continue;
> ret = true;
> + /*
> + * Since memcg OOM allows forced charge, we can safely wait
> + * until __mmput() completes.
> + */
> + if (is_memcg_oom(oc))
> + return true;

Oops. If this OOM victim was blocked on some lock which current thread is
holding, waiting forever unconditionally is not safe.

> #ifdef CONFIG_MMU
> /*
> * Since the OOM reaper exists, we can safely wait until
> * MMF_OOM_SKIP is set.
> */
> if (!test_bit(MMF_OOM_SKIP, &mm->flags)) {
> if (!oom_reap_target) {
> get_task_struct(p);
> oom_reap_target = p;
> trace_wake_reaper(p->pid);
> wake_up(&oom_reaper_wait);
> }
> #endif
> continue;
> }
> #endif
> /* We can wait as long as OOM score is decreasing over time. */
> if (!victim_mm_stalling(p, mm))
> continue;
> gaveup = true;
> list_del(&p->oom_victim_list);
> /* Drop a reference taken by mark_oom_victim(). */
> put_task_struct(p);
> }
> if (gaveup)
> debug_show_all_locks();
>
> return ret;
> }
>