linux-kernel - [PATCH] sched/cpuacct: Check for NULL when using task_pt

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Date:	Wed, 6 Apr 2016 21:59:50 +1000
From:	Anton Blanchard <anton@...ba.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	tglx@...utronix.de, efault@....de, htejun@...il.com,
	linux-kernel@...r.kernel.org, tj@...nel.org,
	torvalds@...ux-foundation.org, zhaolei@...fujitsu.com,
	yangds.fnst@...fujitsu.com, hpa@...or.com,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Michael Ellerman <mpe@...erman.id.au>,
	linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH] sched/cpuacct: Check for NULL when using task_pt_regs()

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@...ba.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();