From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932317AbZHZHph (ORCPT ); Wed, 26 Aug 2009 03:45:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753766AbZHZHph (ORCPT ); Wed, 26 Aug 2009 03:45:37 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:56456 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751850AbZHZHpg (ORCPT ); Wed, 26 Aug 2009 03:45:36 -0400 Message-ID: <4A94E7C7.70900@cn.fujitsu.com> Date: Wed, 26 Aug 2009 15:44:07 +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> <4A94D3A8.1090902@cn.fujitsu.com> <1251269207.7538.1217.camel@twins> <1251270092.7538.1226.camel@twins> <4A94DFF4.5030301@cn.fujitsu.com> <1251271588.7538.1235.camel@twins> <4A94E4BA.1030208@cn.fujitsu.com> <1251272385.7538.1238.camel@twins> In-Reply-To: <1251272385.7538.1238.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 >>>>>> Aahh, I see the bug, its only ftrace that knows about the module, not >>>>>> tracepoints themselves, _that_ needs fixing. >>>>> You could possibly do something like: >>>>> >>>>> struct module *tp_mod = __module_address(&some_tp_symbol); >>>>> struct module *cb_mod = __module_text_address(func); >>>>> >>>>> if (tp_mod && tp_mod != cb_mod) { >>>>> ret = try_get_module(tp_mod); >>>>> if (ret) >>>>> goto fail; >>>>> } >>>>> >>>>> in register_trace_##name() or thereabout. >>>>> >>>> Actually I tried it, but it didn't work. As I said, You can't find >>>> any tp symbol when registering tp callback. The same example again: >>>> >>>> In module bar, we have register_trace_foo() >>>> In module foo, we have DEFINE_TRACE(foo) and trace_foo(). >>>> >>>> bar doesn't know any symbol of foo, so it can't bump foo's refcnt, >>> Well, clearly it knows about register_trace_foo() which itself knows at >>> least one symbol that should be in module foo, right? How else could it >>> register a callback in that module (if it were loaded)? >>> >>> It appears to use some intermediate code, in which case the intermediate >>> code knows about foo, which too solves our problem. >>> >>>> *Note: you can load module bar without loading module foo* >>> In which case the tracepoint registration fails, right? >>> >> No, it won't fail. ;) >> >> Instead, when foo is loaded, tracepoint_update_probe_range() will be >> called, and the probe registered in bar will be added to the tracepoint. > > *blink* > > so we'll succeed in registering a tracepoint we know isn't there? > Yeah, try this: # cd sample/tracepoints/ # insmod tracepoint-probe-sample.ko <--- load trace probe firstly # insmod tracepoint-sample.ko <--- load tracepoint secondly # cat /proc/tracepoint-sample cat: /proc/tracepoint-sample: Operation not permitted <-- pls ignore this # dmesg <-- see the output of probe Event is encountered with filename tracepoint-sample Event B is encountered Event B is encountered Event B is encountered Event B is encountered Event B is encountered Event B is encountered Event B is encountered Event B is encountered Event B is encountered Event B is encountered