From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756743AbZHZGTh (ORCPT ); Wed, 26 Aug 2009 02:19:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750950AbZHZGTh (ORCPT ); Wed, 26 Aug 2009 02:19:37 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:63558 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1750883AbZHZGTg (ORCPT ); Wed, 26 Aug 2009 02:19:36 -0400 Message-ID: <4A94D3A8.1090902@cn.fujitsu.com> Date: Wed, 26 Aug 2009 14:18:16 +0800 From: Li Zefan User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1b3pre) Gecko/20090513 Fedora/3.0-2.3.beta2.fc11 Thunderbird/3.0b2 MIME-Version: 1.0 To: Peter Zijlstra CC: Ingo Molnar , Steven Rostedt , Frederic Weisbecker , LKML , Mathieu Desnoyers Subject: Re: [PATCH] tracing/profile: Fix profile_disable vs module_unload References: <20090824092455.GA25267@elte.hu> <1251106058.7538.149.camel@twins> <4A937505.5000209@cn.fujitsu.com> <1251181266.7538.1016.camel@twins> <4A9385AA.508@cn.fujitsu.com> <1251182405.7538.1050.camel@twins> <20090825090558.GC14003@elte.hu> <1251191546.7538.1118.camel@twins> <20090825102215.GC26801@elte.hu> <1251196359.7538.1133.camel@twins> <20090825103907.GB28287@elte.hu> <1251197235.7538.1142.camel@twins> <1251211963.7538.1164.camel@twins> In-Reply-To: <1251211963.7538.1164.camel@twins> 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 CC: Mathieu Peter Zijlstra wrote: > On Tue, 2009-08-25 at 12:47 +0200, Peter Zijlstra wrote: >> On Tue, 2009-08-25 at 12:39 +0200, Ingo Molnar wrote: >> >>>> Do you really wish to burden every tracepoint user with the extra >>>> logic needed to deal with modules? >>> Not necessarily - i'm just outlining why i think that the 'dont >>> allow subsystems to utilize tracepoint callbacks' is a restriction >>> we should not live with voluntarily. >> Well, unless someone has a bright idea that's what it comes down to. > > OK, I still think modules probing their own tracepoints its stupid [*], > but what you could do is iterate the tracepoint's callback list and see > if it has a callback outside of the module code section and then fail > the unload. > I don't think this can work, what if a new callback is registered after this check? Seems there's no syncronization to guarantee the result of the check can remain valid during module unload. And the other proposal that bumping module refcnt in register_tracepoint_xxx(), I found it hard to do so, because register() won't know where the tracepoint is. For example: register_tracepoint_foo() is in module bar, while DEFINE_TRACE(foo) and trace_foo() is in module foo. Note, you're allowed to load bar without foo. The simplest fix is the patch I sent, which you don't like. Maybe Mathieu, the auther of tracepoint, or some one else has some idea? > [*] in the really utterly fundamentally wrong stupid class.