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Date: Fri, 5 Jul 2013 19:26:55 +0200 From: Oleg Nesterov <oleg@...hat.com> To: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> Cc: Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org, "zhangwei(Jovi)" <jovi.zhangwei@...wei.com>, Jiri Olsa <jolsa@...hat.com>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Arnaldo Carvalho de Melo <acme@...stprotocols.net>, Srikar Dronamraju <srikar@...ux.vnet.ibm.com>, Frederic Weisbecker <fweisbec@...il.com>, Ingo Molnar <mingo@...hat.com>, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [RFC][PATCH 3/4] tracing/kprobes: Fail to unregister if probe event files are open On 07/05, Masami Hiramatsu wrote: > > (2013/07/05 3:48), Oleg Nesterov wrote: > > On 07/04, Masami Hiramatsu wrote: > >> > >> 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. And thus we only need to synchronize kprobe_dispatcher()->kprobe_perf_func() path. And afaics kprobe_perf_func() doesn't use anything which can be freed by trace_remove_event_call? > >> OTOH, unregister_kprobe() waits for that. > > > > Yes. > > > > So I think we only need to move kfree(tp->call.print_fmt). OOPS. I was wrong. It seems that ->print_fmt is only for event/format ? Then it is fine to kfree it right after trace_remove_event_call(). > > 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. Yes, but kprobe_trace_func() is really disabled? > 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. Aaaah... I am starting to understand... Even if kprobe_perf_func() is fine, synchronize_sched() is calles _before_ disable_kprobe() and thus it can't synchronize with the handlers which hit this probe after we start synchronize_sched(). Did you mean this or I misssed something else? Thanks! Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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