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

[Anton Blanchard <anton@samba.org>]

task_pt_regs() can return NULL for kernel threads, so add a check.
This fixes an oops at boot on ppc64.

Fixes: d740037fac70 ("sched/cpuacct: Split usage accounting into user_usage and sys_usage")
Signed-off-by: Anton Blanchard <anton@samba.org>
Reported-and-Tested-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
---

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();