From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753832AbZHYGeh (ORCPT ); Tue, 25 Aug 2009 02:34:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752916AbZHYGef (ORCPT ); Tue, 25 Aug 2009 02:34:35 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:54475 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1752342AbZHYGef (ORCPT ); Tue, 25 Aug 2009 02:34:35 -0400 Message-ID: <4A9385AA.508@cn.fujitsu.com> Date: Tue, 25 Aug 2009 14:33:14 +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> <4A937505.5000209@cn.fujitsu.com> <1251181266.7538.1016.camel@twins> In-Reply-To: <1251181266.7538.1016.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() > > Not tracepoint_probe_{un,}register(), in {un,}register_trace_$call(). > Is there any difference? static inline int register_trace_##name(void (*probe)(proto)) \ { \ int ret; \ void (*func)(void) = reg; \ \ ret = tracepoint_probe_register(#name, (void *)probe); \ if (func && !ret) \ func(); \ return ret; \ } > Basically avoid module unload when a tracepoint from that module has > registered callbacks. TRACE_EVENT() won't prevent this. Instead at module unload, a module notifier callback will be called to unregistread those tracepoint callbacks.