Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754840AbbGFL5I (ORCPT ); Mon, 6 Jul 2015 07:57:08 -0400 Received: from mail4.hitachi.co.jp ([133.145.228.5]:48273 "EHLO mail4.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753973AbbGFL5G (ORCPT ); Mon, 6 Jul 2015 07:57:06 -0400 Message-ID: <559A6D0B.9040201@hitachi.com> Date: Mon, 06 Jul 2015 20:56:59 +0900 From: Masami Hiramatsu Organization: Hitachi, Ltd., Japan User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 MIME-Version: 1.0 To: Pratyush Anand , Will Deacon CC: "linux-arm-kernel@lists.infradead.org" , "linux@arm.linux.org.uk" , Catalin Marinas , "linux-kernel@vger.kernel.org" , "wcohen@redhat.com" , "dave.long@linaro.org" , "steve.capper@linaro.org" Subject: Re: Re: [PATCH 1/2] arm64: Blacklist non-kprobe-able symbols References: <9994841a0b0a8194a6dcc1b6af148ba358488c62.1436158027.git.panand@redhat.com> <20150706090323.GB30342@arm.com> <20150706104815.GA17305@dhcppc13.redhat.com> In-Reply-To: <20150706104815.GA17305@dhcppc13.redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2188 Lines: 56 On 2015/07/06 19:48, Pratyush Anand wrote: > On 06/07/2015:10:03:24 AM, Will Deacon wrote: >> On Mon, Jul 06, 2015 at 06:03:21AM +0100, Pratyush Anand wrote: >>> Add all function symbols which are called from do_debug_exception under >>> NOKPROBE_SYMBOL, as they can not kprobed. >> >> It's a shame this has to be so manual, but I suppose it's done on a >> best-effort basis to catch broken probe placement. >> >> If we miss a function and somebody probes it, do we just get stuck in a >> recursive exception, or could we print something suggesting that a symbol >> be annotated as NOKPROBE? > > In some cases we land into a recursive reenter_kprobe: > > echo "p kfree" > /sys/kernel/debug/tracing/kprobe_events > echo "p single_step_handler" >> /sys/kernel/debug/tracing/kprobe_events > echo 1 > /sys/kernel/debug/tracing/events/enable > > [ 116.904194] BUG: failure at > .../arch/arm64/kernel/kprobes.c:288/reenter_kprobe()! > > In some other > echo "p kfree" > /sys/kernel/debug/tracing/kprobe_events > echo "p el0_sync" >> /sys/kernel/debug/tracing/kprobe_events > echo 1 > /sys/kernel/debug/tracing/events/enable > > Infinite loop of: > [ 142.731336] Unexpected kernel single-step exception at EL1 > > In 1st case currently only address is printed. > pr_warn("Unrecoverable kprobe detected at %p.\n", p->addr); > So, while in 1st case we may also print name of symbol, we can not do > much in second case. Ah, that's a good point of aarch64 :) > Now, I am running some test with all the symbols in /proc/kallsyms and > I noticed that there might be few more symbols which may not allow > kprobing. So, may be I will resend this series with updates. Sounds good to me :) Thank you for testing! -- Masami HIRAMATSU Linux Technology Research Center, System Productivity Research Dept. Center for Technology Innovation - Systems Engineering Hitachi, Ltd., Research & Development Group E-mail: masami.hiramatsu.pt@hitachi.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/