Messages in this thread | | | Date | Thu, 4 Jul 2013 20:48:13 +0200 | From | Oleg Nesterov <> | Subject | Re: [RFC][PATCH 3/4] tracing/kprobes: Fail to unregister if probe event files are open |
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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.
> 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.
> 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?
Oleg.
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