Michal Hocko wrote: > On Mon 13-06-16 13:19:43, Michal Hocko wrote: > [...] > > I am trying to remember why we are disabling oom killer before kernel > > threads are frozen but not really sure about that right away. > > OK, I guess I remember now. Say that a task would depend on a freezable > kernel thread to get to do_exit (stuck in wait_event etc...). We would > simply get stuck in oom_killer_disable for ever. So we need to address > it a different way. > > One way would be what you are proposing but I guess it would be more > systematic to never call exit_oom_victim on a remote task. After [1] we > have a solid foundation to rely only on MMF_REAPED even when TIF_MEMDIE > is set. It is more code than your patch so I can see a reason to go with > yours if the following one seems too large or ugly. > > [1] http://lkml.kernel.org/r/1466426628-15074-1-git-send-email-mhocko@xxxxxxxxxx > > What do you think about the following? I'm OK with not clearing TIF_MEMDIE from a remote task. But this patch is racy. > @@ -567,40 +612,23 @@ static void oom_reap_task(struct task_struct *tsk) > while (attempts++ < MAX_OOM_REAP_RETRIES && !__oom_reap_task(tsk)) > schedule_timeout_idle(HZ/10); > > - if (attempts > MAX_OOM_REAP_RETRIES) { > - struct task_struct *p; > + tsk->oom_reaper_list = NULL; > > + if (attempts > MAX_OOM_REAP_RETRIES) { attempts > MAX_OOM_REAP_RETRIES would mean that down_read_trylock() continuously failed. But it does not guarantee that the offending task shall not call up_write(&mm->mmap_sem) and arrives at mmput() from exit_mm() (as well as other threads which are blocked at down_read(&mm->mmap_sem) in exit_mm() by the offending task arrive at mmput() from exit_mm()) when the OOM reaper was preempted at this point. Therefore, find_lock_task_mm() in requeue_oom_victim() could return NULL and the OOM reaper could fail to set MMF_OOM_REAPED (and find_lock_task_mm() in oom_scan_process_thread() could return NULL and the OOM killer could fail to select next OOM victim as well) when __mmput() got stuck. So, from the point of view of correctness, there remains an unhandled race window as long as you depend on find_lock_task_mm() not returning NULL. You will again ask "does it really matter/occur", and I can't make progress. > pr_info("oom_reaper: unable to reap pid:%d (%s)\n", > task_pid_nr(tsk), tsk->comm); > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>