sched/accounting: Fix user/system tick double accounting

Now that we're  pointing cpuacct's root cgroup to cpustat and accounting
through task_group_account_field(), we should not access cpustat directly.
Since it is done anyway inside the acessor function, we end up accounting
it twice, which is wrong.

Signed-off-by: Glauber Costa <glommer@parallels.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1322863119-14225-2-git-send-email-glommer@parallels.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/sched/core.c

@@ -2601,22 +2601,18 @@ static inline void task_group_account_field(struct task_struct *p,
 void account_user_time(struct task_struct *p, cputime_t cputime,
 		       cputime_t cputime_scaled)
 {
-	u64 *cpustat = kcpustat_this_cpu->cpustat;
-	u64 tmp;
 	int index;
 
 	/* Add user time to process. */
 	p->utime = cputime_add(p->utime, cputime);
 	p->utimescaled = cputime_add(p->utimescaled, cputime_scaled);
 	account_group_user_time(p, cputime);
 
-	/* Add user time to cpustat. */
-	tmp = cputime_to_cputime64(cputime);
-
 	index = (TASK_NICE(p) > 0) ? CPUTIME_NICE : CPUTIME_USER;
-	cpustat[index] += tmp;
 
+	/* Add user time to cpustat. */
 	task_group_account_field(p, index, cputime);
+
 	/* Account for user time used */
 	acct_update_integrals(p);
 }
@@ -2662,16 +2658,12 @@ static inline
 void __account_system_time(struct task_struct *p, cputime_t cputime,
 			cputime_t cputime_scaled, int index)
 {
-	u64 tmp = cputime_to_cputime64(cputime);
-	u64 *cpustat = kcpustat_this_cpu->cpustat;
-
 	/* Add system time to process. */
 	p->stime = cputime_add(p->stime, cputime);
 	p->stimescaled = cputime_add(p->stimescaled, cputime_scaled);
 	account_group_system_time(p, cputime);
 
 	/* Add system time to cpustat. */
-	cpustat[index] += tmp;
 	task_group_account_field(p, index, cputime);
 
 	/* Account for system time used */