Messages in this thread | ![/](/images/icornerl.gif) | | Subject | Re: [PATCH -mm v2 1/3] mm/oom_kill: remove the wrong fatal_signal_pending() check in oom_kill_process() | From | Tetsuo Handa <> | Date | Fri, 2 Oct 2015 20:32:41 +0900 |
| |
Oleg Nesterov wrote: > On 10/01, Michal Hocko wrote: > > > > zap_process will add SIGKILL to all threads but the > > current which will go on without being killed and if this is not a > > thread group leader then we would miss it. > > Yes. And note that de_thread() does the same. Speaking of oom-killer > this is mostly fine, the execing thread is going to release its old > ->mm and it has already passed the copy_strings() stage which can use > a lot more memory.
So, we have the same wrong fatal_signal_pending() check in out_of_memory()
/* * If current has a pending SIGKILL or is exiting, then automatically * select it. The goal is to allow it to allocate so that it may * quickly exit and free its memory. * * But don't select if current has already released its mm and cleared * TIF_MEMDIE flag at exit_mm(), otherwise an OOM livelock may occur. */ if (current->mm && (fatal_signal_pending(current) || task_will_free_mem(current))) { mark_oom_victim(current); return true; }
because it is possible that T starts the coredump, T sends SIGKILL to P, P calls out_of_memory() on GFP_FS allocation, P misses to set SIGKILL on T?
Since T sends SIGKILL to all clone(CLONE_VM) tasks upon coredump, P needs to do
rcu_read_lock(); for_each_process(p) { if (!process_shares_mm(p, current->mm)) continue; if (unlikely(p->flags & PF_KTHREAD)) continue; if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) continue;
do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, true); } rcu_read_unlock();
after mark_oom_victim(current) in case T is not in the same thread group?
If yes, what happens if some task failed to receive SIGKILL due to p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN condition? Will we hit mm->mmap_sem livelock?
| ![\](/images/icornerr.gif) |