From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751900Ab3K0NXM (ORCPT ); Wed, 27 Nov 2013 08:23:12 -0500 Received: from merlin.infradead.org ([205.233.59.134]:50091 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750972Ab3K0NXJ (ORCPT ); Wed, 27 Nov 2013 08:23:09 -0500 Date: Wed, 27 Nov 2013 14:22:43 +0100 From: Peter Zijlstra To: Steven Rostedt Cc: LKML , Ingo Molnar , Preeti U Murthy , svaidy@linux.vnet.ibm.com, vincent.guittot@linaro.org, bitbucket@online.de, benh@kernel.crashing.org, anton@samba.org, Morten.Rasmussen@arm.com, pjt@google.com, mikey@neuling.org, Linus Torvalds Subject: Re: [BUG] in sched fair on v3.13-rc1+ doing hotplug Message-ID: <20131127132243.GD10022@twins.programming.kicks-ass.net> References: <20131127081345.0cab8b15@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131127081345.0cab8b15@gandalf.local.home> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 27, 2013 at 08:13:45AM -0500, Steven Rostedt wrote: > atomic_inc(&sd->groups->sgp->nr_busy_cpus); <<---- BUG > unlock: > rcu_read_unlock(); > } tip/sched/urgent has this one: --- commit 42eb088ed246a5a817bb45a8b32fe234cf1c0f8b Author: Peter Zijlstra Date: Tue Nov 19 16:41:49 2013 +0100 sched: Avoid NULL dereference on sd_busy Commit 37dc6b50cee9 ("sched: Remove unnecessary iteration over sched domains to update nr_busy_cpus") forgot to clear 'sd_busy' under some conditions leading to a possible NULL deref in set_cpu_sd_state_idle(). Reported-by: Anton Blanchard Cc: Preeti U Murthy Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/20131118113701.GF3866@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar diff --git a/kernel/sched/core.c b/kernel/sched/core.c index c1808606ee5f..a1591ca7eb5a 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4910,8 +4910,9 @@ static void update_top_cache_domain(int cpu) if (sd) { id = cpumask_first(sched_domain_span(sd)); size = cpumask_weight(sched_domain_span(sd)); - rcu_assign_pointer(per_cpu(sd_busy, cpu), sd->parent); + sd = sd->parent; /* sd_busy */ } + rcu_assign_pointer(per_cpu(sd_busy, cpu), sd); rcu_assign_pointer(per_cpu(sd_llc, cpu), sd); per_cpu(sd_llc_size, cpu) = size;