Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760183Ab3GSNit (ORCPT ); Fri, 19 Jul 2013 09:38:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48346 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752517Ab3GSNis (ORCPT ); Fri, 19 Jul 2013 09:38:48 -0400 Date: Fri, 19 Jul 2013 15:33:27 +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: Re: [RFC PATCH V2] tracing: Check f_dentry before accessing event_file/call in inode->i_private Message-ID: <20130719133327.GA21278@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> <20130718145137.GA6014@redhat.com> <51E8CCC0.7030404@hitachi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <51E8CCC0.7030404@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: 1715 Lines: 51 On 07/19, Masami Hiramatsu wrote: > > (2013/07/18 23:51), Oleg Nesterov wrote: > > 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. Ah, I didn't notice your patch adds "file->tr->ref++" into ftrace_event_file_get... So I was wrong in any case, thanks for correcting me. But, > (Just one point, previous ftrace_event_file_get has a racy point > when it does tr->ref++, it should be fixed.) Not sure what do you mean, but unless I missed something again this "tr->ref++" above still looks racy. instance_delete() checks tr->ref first, then it takes event_mutex and removes/kfrees event_files. But this doesn't really matter even if I am right, surely this can be fixed. My only point, imho this is more complex than necessary. In particular, > > 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 :) Yes ;) and this makes the ref-counting even more complex, we use different methods to avoid the races with rmdir and event_remove(). > > 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? Yes, yes. 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/