From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 13863 invoked by alias); 12 Dec 2013 06:02:18 -0000 Mailing-List: contact systemtap-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Post: List-Help: , Sender: systemtap-owner@sourceware.org Received: (qmail 13840 invoked by uid 89); 12 Dec 2013 06:02:15 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.6 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_LOW,SPF_PASS autolearn=ham version=3.3.2 X-HELO: mail7.hitachi.co.jp Received: from mail7.hitachi.co.jp (HELO mail7.hitachi.co.jp) (133.145.228.42) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Thu, 12 Dec 2013 06:02:14 +0000 Received: from mlsv4.hitachi.co.jp (unknown [133.144.234.166]) by mail7.hitachi.co.jp (Postfix) with ESMTP id 8A21137AC9; Thu, 12 Dec 2013 15:02:12 +0900 (JST) Received: from mfilter03.hitachi.co.jp by mlsv4.hitachi.co.jp (8.13.1/8.13.1) id rBC62Cxv006920; Thu, 12 Dec 2013 15:02:12 +0900 Received: from vshuts04.hitachi.co.jp (vshuts04.hitachi.co.jp [10.201.6.86]) by mfilter03.hitachi.co.jp (Switch-3.3.4/Switch-3.3.4) with ESMTP id rBC62BEX002168; Thu, 12 Dec 2013 15:02:11 +0900 Received: from gxml20a.ad.clb.hitachi.co.jp (unknown [158.213.157.160]) by vshuts04.hitachi.co.jp (Postfix) with ESMTP id AAECF14003B; Thu, 12 Dec 2013 15:02:10 +0900 (JST) Received: from [10.198.211.167] by gxml20a.ad.clb.hitachi.co.jp (Switch-3.1.10/Switch-3.1.9) id 5BC602AZS00009C28; Thu, 12 Dec 2013 15:02:10 +0900 Message-ID: <52A9515E.5050505@hitachi.com> Date: Thu, 12 Dec 2013 06:02:00 -0000 From: Masami Hiramatsu User-Agent: Mozilla/5.0 (Windows NT 5.2; rv:13.0) Gecko/20120614 Thunderbird/13.0.1 MIME-Version: 1.0 To: Ingo Molnar Cc: Ananth N Mavinakayanahalli , Sandeepa Prabhu , 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> <20131205102127.GA19923@gmail.com> <52A137B6.6030307@hitachi.com> <20131210152811.GA1195@gmail.com> <52A7CA0A.9060009@hitachi.com> <20131211133423.GB3101@gmail.com> In-Reply-To: <20131211133423.GB3101@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-IsSubscribed: yes X-SW-Source: 2013-q4/txt/msg00399.txt.bz2 (2013/12/11 22:34), Ingo Molnar wrote: > > * Masami Hiramatsu wrote: > >>> So why are annotations needed at all? What can happen if an >>> annotation is missing and a piece of code is probed which is also >>> used by the kprobes code internally - do we crash, lock up, >>> misbehave or handle it safely? >> >> The kprobe has recursion detector, [...] > > It's the 'current_kprobe' percpu variable, checked via > kprobe_running(), right? Right. :) >> [...] but it is detected in the kprobe exception(int3) handler, this >> means that if we put a probe before detecting the recursion, we'll >> do an infinite recursion. > > So only the (presumably rather narrow) code path leading to the > recursion detection code has to be annotated, correct? Yes, correct. >> And also, even if we can detect the recursion, we can't stop the >> kernel, we need to skip the probe. This means that we need to >> recover to the main execution path by doing single step. As you may >> know, since the single stepping involves the debug exception, we >> have to avoid proving on that path too. Or we'll have an infinite >> recursion again. > > I don't see why this is needed: if a "probing is disabled" recursion > flag is set the moment the first probe fires, and if it's only cleared > once all processing is finished, then any intermediate probes should > simply return early from int3 and not fire. No, because the int3 already changes the original instruction. This means that you cannot skip singlestep(or emulate) the instruction which is copied to execution buffer (ainsn->insn), even if you have such the flag. So, kprobe requires the annotations on the singlestep path. Thank you, -- Masami HIRAMATSU IT Management Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu.pt@hitachi.com