Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757597Ab3GERbw (ORCPT ); Fri, 5 Jul 2013 13:31:52 -0400 Received: from mx1.redhat.com ([209.132.183.28]:21922 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752029Ab3GERbv (ORCPT ); Fri, 5 Jul 2013 13:31:51 -0400 Date: Fri, 5 Jul 2013 19:26:55 +0200 From: Oleg Nesterov To: Masami Hiramatsu Cc: Steven Rostedt , linux-kernel@vger.kernel.org, "zhangwei(Jovi)" , Jiri Olsa , Peter Zijlstra , Arnaldo Carvalho de Melo , Srikar Dronamraju , Frederic Weisbecker , Ingo Molnar , Andrew Morton Subject: Re: [RFC][PATCH 3/4] tracing/kprobes: Fail to unregister if probe event files are open Message-ID: <20130705172655.GA18576@redhat.com> References: <20130704033347.807661713@goodmis.org> <20130704034038.819592356@goodmis.org> <51D56E74.3090404@hitachi.com> <20130704184813.GA2695@redhat.com> <51D6351A.2000206@hitachi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <51D6351A.2000206@hitachi.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1871 Lines: 63 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@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/