From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from hr2.samba.org (hr2.samba.org [IPv6:2a01:4f8:192:486::147:1]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3qg47905zxzDq6S for ; Wed, 6 Apr 2016 22:00:53 +1000 (AEST) 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> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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();