Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932469Ab3GRO4x (ORCPT ); Thu, 18 Jul 2013 10:56:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48436 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932074Ab3GRO4w (ORCPT ); Thu, 18 Jul 2013 10:56:52 -0400 Date: Thu, 18 Jul 2013 16:51:37 +0200 From: Oleg Nesterov To: Masami Hiramatsu 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: [RFC PATCH V2] tracing: Check f_dentry before accessing event_file/call in inode->i_private Message-ID: <20130718145137.GA6014@redhat.com> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <51E750F4.5070200@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: 1567 Lines: 42 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. 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. 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. > > 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 ;) 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/