From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760108Ab3LFX0H (ORCPT ); Fri, 6 Dec 2013 18:26:07 -0500 Received: from mail4.hitachi.co.jp ([133.145.228.5]:45170 "EHLO mail4.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760093Ab3LFX0D (ORCPT ); Fri, 6 Dec 2013 18:26:03 -0500 Message-ID: <52A25CF0.9030706@hitachi.com> Date: Sat, 07 Dec 2013 08:25:36 +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: Sandeepa Prabhu Cc: Ingo Molnar , Ananth N Mavinakayanahalli , x86@kernel.org, lkml , "Steven Rostedt (Red Hat)" , systemtap@sourceware.org, "David S. Miller" Subject: Re: [PATCH -tip v4 0/6] kprobes: introduce NOKPROBE_SYMBOL() and fixes crash bugs References: <20131204012841.22118.82992.stgit@kbuild-fedora.novalocal> <20131204084551.GA31772@gmail.com> <529FBA71.6070107@hitachi.com> <52A16D49.9050105@hitachi.com> In-Reply-To: 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 (2013/12/06 15:54), Sandeepa Prabhu wrote: >>> I am not sure if this question is related, uprobes or ftrace code does >>> not define __kprobes, so is it safe to place kprobe on uprobes or >>> ftrace code? >> >> Yes, it is "safe" in qualitative meaning. But for ftrace code, it could >> give a performance impact by miss-hitting. Since uprobe is independent >> from kprobe, it should work. >> >>> Is it expected from arch code to support such cases? >> >> Yes, the arch dependent implementation is the key. If it shares some >> code which can be called from miss-hit path, it should be blacklisted. > well, isn't the blacklist only for those routines that can not be > handled or may crash kernel, like the code sections called from > exception kprobes exception handlers etc? Yes, that's why the blacklist is needed. > suppose if the probe on routine can miss-hit (probes re-cursing) but > can be handled, it's only a quantitative issue (i.e. performance > impact) so it should be *user's* problem right? I mean, as you said > earlier about having white-list or a performance gatekeeper > (systemtap), one can avoid such cases by white list or removing > miss-hit probes dynamically. But a blacklisting a symbol means > placing a probe on that *can not be handled* and can crash the system, > is it correct? Yes, exactly that is what I meant. :) The blacklist is only for avoiding such fundamental issue, therefore, it strongly depends on the architecture code. Thank you, -- Masami HIRAMATSU IT Management Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu.pt@hitachi.com