Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932561AbcDFMAh (ORCPT ); Wed, 6 Apr 2016 08:00:37 -0400 Received: from hr2.samba.org ([144.76.82.148]:51940 "EHLO hr2.samba.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754899AbcDFMAf (ORCPT ); Wed, 6 Apr 2016 08:00:35 -0400 Date: Wed, 6 Apr 2016 21:59:50 +1000 From: Anton Blanchard To: Peter Zijlstra Cc: Ingo Molnar , Srikar Dronamraju , tglx@linutronix.de, efault@gmx.de, htejun@gmail.com, linux-kernel@vger.kernel.org, tj@kernel.org, torvalds@linux-foundation.org, zhaolei@cn.fujitsu.com, yangds.fnst@cn.fujitsu.com, hpa@zytor.com, Stephen Rothwell , Michael Ellerman , linuxppc-dev@lists.ozlabs.org Subject: [PATCH] sched/cpuacct: Check for NULL when using task_pt_regs() Message-ID: <20160406215950.04bc3f0b@kryten> In-Reply-To: <20160406110803.GI2906@worktop> References: <20160404140312.GA28495@linux.vnet.ibm.com> <20160406065436.GB3078@gmail.com> <20160406203219.788ae7cf@kryten> <20160406110803.GI2906@worktop> X-Mailer: Claws Mail 3.12.0 (GTK+ 2.24.28; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 983 Lines: 43 Hi Peter, > Ah, so sometihng like: > > struct pt_regs *regs = task_pt_regs(); > int index = CPUACCT_USAGE_SYSTEM; > > if (regs && user_mode(regs)) > index = CPUACCT_USAGE_USER; > > should work, right? Looks good, and the patch below does fix the oops for me. Anton -- task_pt_regs() can return NULL for kernel threads, so add a check. This fixes an oops at boot on ppc64. Signed-off-by: Anton Blanchard --- diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c index df947e0..41f85c4 100644 --- a/kernel/sched/cpuacct.c +++ b/kernel/sched/cpuacct.c @@ -316,12 +316,11 @@ static struct cftype files[] = { void cpuacct_charge(struct task_struct *tsk, u64 cputime) { struct cpuacct *ca; - int index; + int index = CPUACCT_USAGE_SYSTEM; + struct pt_regs *regs = task_pt_regs(tsk); - if (user_mode(task_pt_regs(tsk))) + if (regs && user_mode(regs)) index = CPUACCT_USAGE_USER; - else - index = CPUACCT_USAGE_SYSTEM; rcu_read_lock();