Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758843Ab3CGDpl (ORCPT ); Wed, 6 Mar 2013 22:45:41 -0500 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:38597 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753033Ab3CGDpk (ORCPT ); Wed, 6 Mar 2013 22:45:40 -0500 Date: Thu, 7 Mar 2013 03:44:55 +0000 From: Will Deacon To: Ming Lei Cc: "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Tejun Heo , Peter Zijlstra , Ingo Molnar , "rob.herring@calxeda.com" , Nicolas Pitre , Russell King Subject: Re: [RFC PATCH] ARM: keep __my_cpu_offset consistent with generic one Message-ID: <20130307034454.GE25137@mudshark.cambridge.arm.com> References: <1362624468-5451-1-git-send-email-tom.leiming@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1362624468-5451-1-git-send-email-tom.leiming@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1229 Lines: 28 Hello, On Thu, Mar 07, 2013 at 02:47:48AM +0000, Ming Lei wrote: > Commit 14318efb(ARM: 7587/1: implement optimized percpu variable access) > introduces arm's __my_cpu_offset to optimize percpu vaiable access, > which really works well on hackbench test, but may cause __my_cpu_offset > to return garbage value before it is initialized in cpu_init() called > by setup_arch, so accessing a percpu variable before setup_arch may cause > kernel hang. But the generic__my_cpu_offset always returns zero before > percpu area is brought up. > > So the patch tries to clear __my_cpu_offset on boot CPU early > to avoid boot hang. > > At least now percpu variable is accessed by lockdep before > setup_arch(), and enabling CONFIG_LOCK_STAT or CONFIG_DEBUG_LOCKDEP > can trigger kernel hang. For the record, can you include a backtrace or something please? The description makes it sounds like a caller bug, so it would be good to document a valid user of per-cpu before cpu_init(). Will -- 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/