On Sat 06-12-14 08:06:57, Tejun Heo wrote: > Hello, > > On Fri, Dec 05, 2014 at 05:41:44PM +0100, Michal Hocko wrote: > > oom_kill_process only sets TIF_MEMDIE flag and sends a signal to the > > victim. This is basically noop when the task is frozen though because > > the task sleeps in uninterruptible sleep. The victim is eventually > > thawed later when oom_scan_process_thread meets the task again in a > > later OOM invocation so the OOM killer doesn't live lock. But this is > > less than optimal. Let's add the frozen check and thaw the task right > > before we send SIGKILL to the victim. > > > > The check and thawing in oom_scan_process_thread has to stay because the > > task might got access to memory reserves even without an explicit > > SIGKILL from oom_kill_process (e.g. it already has fatal signal pending > > or it is exiting already). > > How else would a task get TIF_MEMDIE? If there are other paths which > set TIF_MEMDIE, the right thing to do is creating a function which > thaws / wakes up the target task and use it there too. Please > interlock these things properly from the get-go instead of scattering > these things around. See __out_of_memory which sets TIF_MEMDIE on current when it is exiting or has fatal signals pending. This task cannot be frozen obviously. > > @@ -545,6 +545,8 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order, > > rcu_read_unlock(); > > > > mark_tsk_oom_victim(victim); > > + if (frozen(victim)) > > + __thaw_task(victim); > > The frozen() test here is racy. Always calling __thaw_task() wouldn't > be. You can argue that being racy here is okay because the later > scanning would find it but why complicate things like that? Just > properly interlock each instance and be done with it. OK, changed. I didn't realize that __thaw_task does the check already and was following what we have in oom_scan_process_thread. Removed the check from that one as well. -- 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>