From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754383AbaIBQVQ (ORCPT ); Tue, 2 Sep 2014 12:21:16 -0400 Received: from e34.co.us.ibm.com ([32.97.110.152]:50092 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753703AbaIBQVP (ORCPT ); Tue, 2 Sep 2014 12:21:15 -0400 Date: Tue, 2 Sep 2014 09:21:10 -0700 From: "Paul E. McKenney" To: Christoph Lameter Cc: Fengguang Wu , Jet Chen , Su Tao , Yuanhan Liu , LKP , linux-kernel@vger.kernel.org Subject: Re: [percpu] BUG: unable to handle kernel NULL pointer dereference at (null) Message-ID: <20140902162110.GB5001@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20140902045830.GA11321@localhost> <20140902153403.GY5001@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14090216-1542-0000-0000-0000047966CA Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 02, 2014 at 11:00:12AM -0500, Christoph Lameter wrote: > On Tue, 2 Sep 2014, Paul E. McKenney wrote: > > > Before this commit, raw_cpu_add_return() didn't build. The commit > > didn't affect anything else. > > > > So I don't understand how anything could work before this commit and > > be broken after it. Enlightenment? > > Where is that raw_cpu_add_return statement? > > grep does not match anything like that in kernel/rcu/* > and this_cpu_add_return is used extensively in the network subsystem for > statistics. Heh! Good point! Added by ac1bea85781e (sched,rcu: Make cond_resched() report RCU quiescent states), removed by 4a81e8328d379 (rcu: Reduce overhead of cond_resched() checks for RCU). So, as you say, no effect on contemporary kernels. Thanx, Paul