[S390] cputime: initialize per thread timer values on fork

Initialize per thread timer values instead of just copying them from
the parent. That way it is easily possible to tell how much time a
thread spent in user/system context.
Doesn't fix a bug, this is just for debugging purposes.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/process.c

@@ -163,6 +163,7 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long new_stackp,
 		unsigned long unused,
 		struct task_struct *p, struct pt_regs *regs)
 {
+	struct thread_info *ti;
 	struct fake_frame
 	{
 		struct stack_frame sf;
@@ -214,6 +215,10 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long new_stackp,
 	p->thread.mm_segment = get_fs();
 	/* Don't copy debug registers */
 	memset(&p->thread.per_info, 0, sizeof(p->thread.per_info));
+	/* Initialize per thread user and system timer values */
+	ti = task_thread_info(p);
+	ti->user_timer = 0;
+	ti->system_timer = 0;
 	return 0;
 }