From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755641AbZHZHkw (ORCPT ); Wed, 26 Aug 2009 03:40:52 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753487AbZHZHkv (ORCPT ); Wed, 26 Aug 2009 03:40:51 -0400 Received: from casper.infradead.org ([85.118.1.10]:42265 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752647AbZHZHku (ORCPT ); Wed, 26 Aug 2009 03:40:50 -0400 Subject: Re: [PATCH] tracing/profile: Fix profile_disable vs module_unload From: Peter Zijlstra To: Li Zefan Cc: Ingo Molnar , Steven Rostedt , Frederic Weisbecker , LKML , Mathieu Desnoyers In-Reply-To: <4A94E4BA.1030208@cn.fujitsu.com> 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> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Wed, 26 Aug 2009 09:39:45 +0200 Message-Id: <1251272385.7538.1238.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.26.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2009-08-26 at 15:31 +0800, Li Zefan wrote: > 15:26, Peter Zijlstra wrote: > > On Wed, 2009-08-26 at 15:10 +0800, Li Zefan wrote: > >> Peter Zijlstra wrote: > >>> On Wed, 2009-08-26 at 08:46 +0200, Peter Zijlstra wrote: > >>> > >>>> 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?