On Tue 23-12-14 20:46:07, Tetsuo Handa wrote: > Michal Hocko wrote: > > > Also, why not to call set_tsk_thread_flag() and do_send_sig_info() together > > > like below > > > > What would be an advantage? I am not really sure whether the two locks > > might nest as well. > > I imagined that current thread sets TIF_MEMDIE on a victim thread, then > sleeps for 30 seconds immediately after task_unlock() (it's an overdone > delay), Only if the current task was preempted for such a long time. Which doesn't sound too probable to me. > and finally sets SIGKILL on that victim thread. If such a delay > happened, that victim thread is free to abuse TIF_MEMDIE for that period. > Thus, I thought sending SIGKILL followed by setting TIF_MEMDIE is better. I don't know, I can hardly find a scenario where it would make any difference in the real life. If the victim needs to allocate a memory to finish then it would trigger OOM again and have to wait/loop until this OOM killer releases the oom zonelist lock just to find out it already has TIF_MEMDIE set and can dive into memory reserves. Which way is more correct is a question but I wouldn't change it without having a really good reason. This whole code is subtle already, let's not make it even more so. > > rcu_read_unlock(); > > - set_tsk_thread_flag(victim, TIF_MEMDIE); > do_send_sig_info(SIGKILL, SEND_SIG_FORCED, victim, true); > + task_lock(victim); > + if (victim->mm) > + set_tsk_thread_flag(victim, TIF_MEMDIE); > + task_unlock(victim); > put_task_struct(victim); > > If such a delay is theoretically impossible, I'm OK with your patch. -- Michal Hocko SUSE Labs -- 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>