wait_task_zombie: do not use thread_group_cputime()

There is no reason for thread_group_cputime() in wait_task_zombie(), there
must be no other threads.

This call was previously needed to collect the per-cpu data which we do
not have any longer.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Roland McGrath <roland@redhat.com>
Cc: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: Vitaly Mayatskikh <vmayatsk@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/exit.c

@@ -1191,7 +1191,6 @@ static int wait_task_zombie(struct task_struct *p, int options,
 	if (likely(!traced)) {
 		struct signal_struct *psig;
 		struct signal_struct *sig;
-		struct task_cputime cputime;
 
 		/*
 		 * The resource counters for the group leader are in its
@@ -1207,23 +1206,20 @@ static int wait_task_zombie(struct task_struct *p, int options,
 		 * need to protect the access to parent->signal fields,
 		 * as other threads in the parent group can be right
 		 * here reaping other children at the same time.
-		 *
-		 * We use thread_group_cputime() to get times for the thread
-		 * group, which consolidates times for all threads in the
-		 * group including the group leader.
 		 */
-		thread_group_cputime(p, &cputime);
 		spin_lock_irq(&p->real_parent->sighand->siglock);
 		psig = p->real_parent->signal;
 		sig = p->signal;
 		psig->cutime =
 			cputime_add(psig->cutime,
-			cputime_add(cputime.utime,
-				    sig->cutime));
+			cputime_add(p->utime,
+			cputime_add(sig->utime,
+				    sig->cutime)));
 		psig->cstime =
 			cputime_add(psig->cstime,
-			cputime_add(cputime.stime,
-				    sig->cstime));
+			cputime_add(p->stime,
+			cputime_add(sig->stime,
+				    sig->cstime)));
 		psig->cgtime =
 			cputime_add(psig->cgtime,
 			cputime_add(p->gtime,