sched: keep utime/stime monotonic

keep utime/stime monotonic.

cpustats use utime/stime as a ratio against sum_exec_runtime, as a
consequence it can happen - when the ratio changes faster than time
accumulates - that either can be appear to go backwards.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/fork.c b/kernel/fork.c
index ddafdfa..a65bfc4 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1056,6 +1056,7 @@
 	p->gtime = cputime_zero;
 	p->utimescaled = cputime_zero;
 	p->stimescaled = cputime_zero;
+	p->prev_utime = cputime_zero;
 
 #ifdef CONFIG_TASK_XACCT
 	p->rchar = 0;		/* I/O counter: bytes read */