(2013/07/05 3:48), Oleg Nesterov wrote: > On 07/04, Masami Hiramatsu wrote: >> >> (2013/07/04 12:33), Steven Rostedt wrote: >>> + /* Will fail if probe is being used by ftrace or perf */ >>> + if (unregister_probe_event(tp)) >>> + return -EBUSY; >>> + >>> __unregister_trace_probe(tp); >>> list_del(&tp->list); >>> - unregister_probe_event(tp); >>> >>> return 0; >>> } >> >> This may cause an unexpected access violation at kprobe handler because >> unregister_probe_event frees event_call/event_files and it will be >> accessed until kprobe is *completely* disabled. > > I don't think so... Please correct me. > > (but yes I think the patch needs a small update, see below). > >> Actually disable_kprobe() doesn't ensure to finish the current running >> kprobe handlers. > > Yes. in fact disable_trace_probe(file != NULL) does, but perf doesn't.
Ah, right. we did that. > >> Thus, even if trace_probe_is_enabled() returns false, >> we must do synchronize_sched() for waiting, before unregister_probe_event(). > > No, I think we should simply kill trace_probe_is_enabled() here. > And synchronize_sched() _before_ unregister_probe_event() can't > help, exactly because trace_probe_is_enabled() is racy. Right, it should be useless. >> OTOH, unregister_kprobe() waits for that. > > Yes. > > So I think we only need to move kfree(tp->call.print_fmt). In fact I > already wrote the patch assuming that trace_remove_event_call() will > be changed as we discussed. > > So the sequence should be: > > if (trace_remove_event_call(...)) > return; > > /* does synchronize_sched */ > unregister_kprobe(); > > kfree(everything); > > Agreed? If we can free everything after all, I'd like to do so. Hmm, but AFAICS, trace_remove_event_call() supposes that all event is disabled completely. A safe way is to wait rcu always right after disable_*probe in disable_trace_probe. If we have an unused link, we can free it after that. Or, do more aggressively, introducing a dying-bit for each trace-probe could be another way. If the bit is set, all enable operations are failed. It works like as a per-event lock. Thank you, -- Masami HIRAMATSU IT Management Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: [email protected] -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
