[PATCH] sched/cpuacct: Check for NULL when using task_pt_regs()

From: Anton Blanchard <anton@samba.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>,
	Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
	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 <sfr@canb.auug.org.au>,
	Michael Ellerman <mpe@ellerman.id.au>,
	linuxppc-dev@lists.ozlabs.org
Subject: [PATCH] sched/cpuacct: Check for NULL when using task_pt_regs()
Date: Wed, 6 Apr 2016 21:59:50 +1000	[thread overview]
Message-ID: <20160406215950.04bc3f0b@kryten> (raw)
In-Reply-To: <20160406110803.GI2906@worktop>

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 <anton@samba.org>
---

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();
 
