From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759038AbYFXIh5 (ORCPT ); Tue, 24 Jun 2008 04:37:57 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752884AbYFXIhs (ORCPT ); Tue, 24 Jun 2008 04:37:48 -0400 Received: from rv-out-0506.google.com ([209.85.198.227]:60677 "EHLO rv-out-0506.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752217AbYFXIhr (ORCPT ); Tue, 24 Jun 2008 04:37:47 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version :content-type:content-transfer-encoding:content-disposition :references; b=WN/tWKqYN1+l/wRbx3ran88xrFCahroh/K6b9D0wYqNu2070yvIw0yG7zeRK3kbQNz aaWKB3OTt/gXQ2MQIaywT3j8z7T1t70tE/kRek2SV8Fn7qHYkKJkX61tHgdExEJ3UIIt O/1wi1/FoBVpRURCnvQNAR880NAl/Jou5nVBo= Message-ID: <19f34abd0806240137w31191b67t45e243a208cba933@mail.gmail.com> Date: Tue, 24 Jun 2008 10:37:46 +0200 From: "Vegard Nossum" To: "Zhang, Yanmin" Subject: Re: v2.6.26-rc7: BUG: unable to handle kernel NULL pointer dereference Cc: "Rusty Russell" , "Mike Travis" , "Adrian Bunk" , "Srivatsa Vaddagiri" , linux-kernel@vger.kernel.org, "Gautham R Shenoy" , "Rafael J. Wysocki" , "Zhang, Yanmin" , "Heiko Carstens" In-Reply-To: <1214294783.25608.75.camel@ymzhang> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline References: <20080622125633.GA8166@damson.getinternet.no> <200806231326.11328.rusty@rustcorp.com.au> <485FD644.80208@sgi.com> <200806241136.52430.rusty@rustcorp.com.au> <1214294783.25608.75.camel@ymzhang> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from base64 to 8bit by alpha.home.local id m5O8c1fq009369 On Tue, Jun 24, 2008 at 10:06 AM, Zhang, Yanmin wrote:> In function _cpu_up, the panic happens when calling __raw_notifier_call_chain> at the second time. Kernel doesn't panic when calling it at the first time. If> just say because of nr_cpu_ids, that's not right.>> By checking source codes, I find function do_boot_cpu is the culprit.> Consider below call chain:> _cpu_up=>__cpu_up=>smp_ops.cpu_up=>native_cpu_up=>do_boot_cpu.>> So do_boot_cpu is called in the end. In do_boot_cpu, if boot_error==true,> cpu_clear(cpu, cpu_possible_map) is executed. So later on, when _cpu_up> calls __raw_notifier_call_chain at the second time to report CPU_UP_CANCELED,> because this cpu is already cleared from cpu_possible_map, get_cpu_sysdev returns> NULL. Ahhha! Well done! (Whew, I have a lot to learn :-D) >> Many resources are related to cpu_possible_map, so it's better not to change it.>> Below patch against 2.6.26-rc7 fixes it by removing the bit clearing in cpu_possible_map.>> Vegard, would you like to help test it? Sure, but it can take a while. 1) I have no idea why the processorfailed to initialize in the first place. So far, it only ever happenedthis one time. 2) There seems to be a couple of other failure casesrelated to cpu hotplug (usually the machine freezes hard), so it's notcertain that we hit this (failed to initialize) first. But I will try! Thanks for solving the mystery. Vegard -- "The animistic metaphor of the bug that maliciously sneaked in whilethe programmer was not looking is intellectually dishonest as itdisguises that the error is the programmer's own creation." -- E. W. Dijkstra, EWD1036{.n++%ݶw{.n+{G{ayʇڙ,jfhz_(階ݢj"mG?&~iOzv^m ?I