From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756986Ab3GRISd (ORCPT ); Thu, 18 Jul 2013 04:18:33 -0400 Received: from mail7.hitachi.co.jp ([133.145.228.42]:55364 "EHLO mail7.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756725Ab3GRIS3 (ORCPT ); Thu, 18 Jul 2013 04:18:29 -0400 Message-ID: <51E7A4CF.2050404@hitachi.com> Date: Thu, 18 Jul 2013 17:18:23 +0900 From: Masami Hiramatsu Organization: Hitachi, Ltd., Japan User-Agent: Mozilla/5.0 (Windows NT 5.2; rv:13.0) Gecko/20120614 Thunderbird/13.0.1 MIME-Version: 1.0 To: Oleg Nesterov Cc: Steven Rostedt , "zhangwei(Jovi)" , Jiri Olsa , Peter Zijlstra , Arnaldo Carvalho de Melo , Srikar Dronamraju , Frederic Weisbecker , Ingo Molnar , Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 0/4] tracing: fix open/delete fixes References: <20130716185658.GA21167@redhat.com> <51E6032B.7070907@hitachi.com> <20130717144357.GA7358@redhat.com> In-Reply-To: <20130717144357.GA7358@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (2013/07/17 23:43), Oleg Nesterov wrote: > On 07/17, Masami Hiramatsu wrote: >> >> At a glance, you're trying to change which operation will be >> failed. Currently, user can not remove an event while someone >> opens files which related to the event. And this approach >> changes that the someone can remove the event even if the >> files are opened (and read/write operation will be failed). >> Am I understand correctly? > > Yes. > > Once again, I am still not sure and I am asking for your review. OK, > But to me this looks much better. To simplify the discussion, lets > consider ftrace_enable_fops in particular. > > - Why should .open() block rmdir or unregister_uprobe_event? Because it is opened and under preparing for use. :) But, yeah, if we expect there is only one user using ftrace, accessing the removing event file is meaningless. It should be failed. > - Why do we need .open() at all? Whatever it can do to > validate file/call/etc, .read/write can do the same. Currently, just for preparing and reserving. > - If we kill .open/release, we do not need the nontrivial > refcounting. Everything becomes simple, no need to keep > the state "in between". That also means to refrain checking existence under locking mutex in all operations. And we have to check it, which I actually concern. refcounting is not so small and itself is complex, but it just needs to inc/dec on open/close. > We need event_mutex anyway (and note that other f_op's can > also rely on other locks taken by trace_remove_event_call), > the validation degrades to the trivial != NULL check. > > - This also simplifies trace_remove_event_call() paths, we > know that once it takes event_mutex nobody can play with > ftrace_event_file/ftrace_event_call we are going to free. Hmm, it seems that we can remove only refcount check, or more? Thank you, -- Masami HIRAMATSU IT Management Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu.pt@hitachi.com