From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759452Ab3GSFVM (ORCPT ); Fri, 19 Jul 2013 01:21:12 -0400 Received: from mail9.hitachi.co.jp ([133.145.228.44]:34419 "EHLO mail9.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753140Ab3GSFVK (ORCPT ); Fri, 19 Jul 2013 01:21:10 -0400 Message-ID: <51E8CCC0.7030404@hitachi.com> Date: Fri, 19 Jul 2013 14:21:04 +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 , Peter Zijlstra , Frederic Weisbecker , linux-kernel@vger.kernel.org, Ingo Molnar , Arnaldo Carvalho de Melo , Andrew Morton , jovi.zhangwei@huawei.com, Jiri Olsa , Srikar Dronamraju Subject: Re: Re: [RFC PATCH V2] tracing: Check f_dentry before accessing event_file/call in inode->i_private References: <20130705003223.GA4981@redhat.com> <20130709075519.2583.96462.stgit@mhiramat-M0-7522> <20130715181659.GA18505@redhat.com> <51E5FD33.4040604@hitachi.com> <20130717145148.GB7358@redhat.com> <51E750F4.5070200@hitachi.com> <20130718145137.GA6014@redhat.com> In-Reply-To: <20130718145137.GA6014@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 (2013/07/18 23:51), Oleg Nesterov wrote: > On 07/18, Masami Hiramatsu wrote: >> >> (2013/07/17 23:51), Oleg Nesterov wrote: >>> Well, perhaps you are right... But this TRACE_EVENT_FL_REF_MASK code >>> is new too, it is not that we only need a small fixlets to finish it. >> >> Would you mean that TRACE_EVENT_FL_REF_MASK may also have some problems? > > It was you who initially pointed that it does have problems ;) > > And, _afaics_ your patch which tries to fix this problem is not > exactly correct. Hm, > It removes trace_array_get/put from tracing_open_generic_file() and > tracing_release_generic_file(). This assumes that "call->flags++" is > enough, but it is not. No, it replaces trace_array_get/put with ftrace_event_file_get/put which calls trace_array_get/put inside. (Just one point, previous ftrace_event_file_get has a racy point when it does tr->ref++, it should be fixed.) > Yes, the next patch adds the "flags & TRACE_EVENT_FL_REF_MASK" check > into trace_remove_event_call() path. But this is still racy wrt > instance_delete() unless I missed something. > > IOW, I believe that either .open() should do trace_array_get(), or > __trace_remove_event_dirs() needs another for-each-file loop which > checks file->call->flags & TRACE_EVENT_FL_REF_MASK. Agreed :) >>> So I think that it makes sense to discuss the alternatives before we >>> decide what exactly we should do. >> >> Your approach is also interesting for me, indeed. However, it is so >> different from current one. I think you should clarify what bug you >> would like to solve and how. > > The same bugs which Steven's 1/4 tries to solve ;) OK, let me confirm that, would you mean we still need 2/4 - 4/4? Thank you, -- Masami HIRAMATSU IT Management Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu.pt@hitachi.com