sched/cputime: Fix accounting on multi-threaded processes

Recent commit 6fac4829 ("cputime: Use accessors to read task
cputime stats") introduced a bug, where we account many times
the cputime of the first thread, instead of cputimes of all
the different threads.

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20130404085740.GA2495@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/cputime.c

@@ -310,7 +310,7 @@ void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times)
 
 	t = tsk;
 	do {
-		task_cputime(tsk, &utime, &stime);
+		task_cputime(t, &utime, &stime);
 		times->utime += utime;
 		times->stime += stime;
 		times->sum_exec_runtime += task_sched_runtime(t);