From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754506AbZHYFXh (ORCPT ); Tue, 25 Aug 2009 01:23:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754492AbZHYFXg (ORCPT ); Tue, 25 Aug 2009 01:23:36 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:51838 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1754489AbZHYFXe (ORCPT ); Tue, 25 Aug 2009 01:23:34 -0400 Message-ID: <4A937505.5000209@cn.fujitsu.com> Date: Tue, 25 Aug 2009 13:22:13 +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 Subject: Re: [PATCH] tracing/profile: Fix profile_disable vs module_unload References: <4A9214E3.2070807@cn.fujitsu.com> <1251093660.7538.119.camel@twins> <4A923197.4040708@cn.fujitsu.com> <1251097012.7538.123.camel@twins> <20090824092455.GA25267@elte.hu> <1251106058.7538.149.camel@twins> In-Reply-To: <1251106058.7538.149.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 >>>>>> If the correspoding module is unloaded before ftrace_profile_disable() >>>>>> is called, event->profile_disable() won't be called, which can >>>>>> cause oops: >>>>>> >>>>>> # insmod trace-events-sample.ko >>>>>> # perf record -f -a -e sample:foo_bar sleep 3 & >>>>>> # sleep 1 >>>>>> # rmmod trace_events_sample >>>>>> # insmod trace-events-sample.ko >>>>>> OOPS! >>>>>> >>>>>> Signed-off-by: Li Zefan >>>>> >>>>> Hrmm, feel fragile, why don't we check if all a modules tracepoints are >>>>> unused on unload? >>>>> >>>> I don't think it's fragile. We are profiling via a module's >>>> tracepoint, so we should pin the module, via module_get(). >>>> If event->profile_enable() has been calld, we should make >>>> sure it's profile_disable() will be called. >>> What I call fragile is that everyone registering a tracepoint >>> callback will now apparently need to worry about modules, _that_ >>> is fragile. >>> >>> Either make module unload look at tracepoint users, or place the >>> try_get_module() in the registration hooks so that regular users >>> don't need to worry about it. >> The bug found by Li needs to be fixed obviously. >> >> I tend to agree with you that this does not appear to be the best >> place to do it: so you suggest to implicitly increase the module >> refcount on callback registr instead? (and releasing it when >> unregistering) >> >> Same end result, slightly cleaner place to bump the refcount. > > Yes, because the user of tracepoints should never need to care about > modules. > I'm afraid it is not feasible to bump module refcnt implicitly in tracepoint_probe_register(). If a tracepoint is registered in module_init, and unregistered in module_exit (see sample/tracepoints), the module is unloadable: insmod ->call mod->init() ->trace_reg_foo() ->module_get() rmmod ->check mod refcnt ->call mod->exit() ->trace_unreg_foo() ->module_put()