From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755259Ab3KOBQ1 (ORCPT ); Thu, 14 Nov 2013 20:16:27 -0500 Received: from mail7.hitachi.co.jp ([133.145.228.42]:53265 "EHLO mail7.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753658Ab3KOBQV (ORCPT ); Thu, 14 Nov 2013 20:16:21 -0500 Message-ID: <528575E2.4000700@hitachi.com> Date: Fri, 15 Nov 2013 10:16:18 +0900 From: Masami Hiramatsu Organization: Hitachi, Ltd., Japan User-Agent: Mozilla/5.0 (Windows NT 5.2; rv:13.0) Gecko/20120614 Thunderbird/13.0.1 MIME-Version: 1.0 To: Peter Zijlstra Cc: Frederic Weisbecker , Vince Weaver , Steven Rostedt , LKML , Ingo Molnar , Dave Jones Subject: Re: perf/tracepoint: another fuzzer generated lockup References: <20131108200244.GB14606@localhost.localdomain> <20131108204839.GD14606@localhost.localdomain> <20131108223657.GF14606@localhost.localdomain> <20131109151014.GN16117@laptop.programming.kicks-ass.net> <20131114152304.GC5364@laptop.programming.kicks-ass.net> <20131114153301.GD5364@laptop.programming.kicks-ass.net> In-Reply-To: <20131114153301.GD5364@laptop.programming.kicks-ass.net> 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 (2013/11/15 0:33), Peter Zijlstra wrote: > On Thu, Nov 14, 2013 at 04:23:04PM +0100, Peter Zijlstra wrote: >> /* >> + * We must dis-allow sampling irq_work_exit() because perf event sampling >> + * itself can cause irq_work, which would lead to an infinite loop; >> + * >> + * 1) irq_work_exit happens >> + * 2) generates perf sample >> + * 3) generates irq_work >> + * 4) goto 1 >> + */ >> +TRACE_EVENT_PERF_PERM(irq_work_exit, is_sampling_event(p_event) ? -EPERM : 0); > > And the only reason this doesn't feed fwd itself into oblivion for > irq_work_enter() is because the irq_work_list must not be empty when the > interrupt is raised, and queueing further work does not re-raise the > IPI. > > > Also, we should probably do something 'smart' for kprobes, as all of > irq_work.c and plenty of perf itself is not __kprobe marked so you're > all free to insert kprobes in the middle of perf and then attach perf to > such a thing. Kprobes itself can detect nested call by using per-cpu current-running kprobe pointer. And if it is nested, it just skips calling handlers. Anyway, I don't recommend to probe inside the handlers, but yes, you can trace perf-handler by ftrace B). I actually traced a kprobe-bug by kprobe-tracer last night, that was amazing :) Thank you, -- Masami HIRAMATSU IT Management Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu.pt@hitachi.com