Revert "sched/cputime: Refactor the cputime_adjust() code"

This reverts commit 72298e5c.

As Peter explains:

> Argh, no... That code was perfectly fine. The new code otoh is
> convoluted.
>
> The old code had the following form:
>
>         if (exception1)
>           deal with exception1
>
>         if (execption2)
>           deal with exception2
>
>         do normal stuff
>
> Which is as simple and straight forward as it gets.
>
> The new code otoh reads like:
>
>         if (!exception1) {
>                 if (exception2)
>                   deal with exception 2
>                 else
>                   do normal stuff
>         }

So restore the old form.

Also fix the comment describing the logic, as it was confusing.
Requested-by: Peter Zijlstra <peterz@infradead.org>
Cc: Gustavo A. R. Silva <garsilva@embeddedor.com>
Cc: Frans Klaver <fransklaver@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wanpeng Li <wanpeng.li@hotmail.com>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/cputime.c

@@ -611,17 +611,23 @@ static void cputime_adjust(struct task_cputime *curr,
 	utime = curr->utime;
 
 	/*
-	 * If either stime or both stime and utime are 0, assume all runtime is
-	 * userspace. Once a task gets some ticks, the monotonicy code at
-	 * 'update' will ensure things converge to the observed ratio.
+	 * If either stime or utime are 0, assume all runtime is userspace.
+	 * Once a task gets some ticks, the monotonicy code at 'update:'
+	 * will ensure things converge to the observed ratio.
 	 */
-	if (stime != 0) {
-		if (utime == 0)
+	if (stime == 0) {
+		utime = rtime;
+		goto update;
+	}
+
+	if (utime == 0) {
 		stime = rtime;
-		else
-			stime = scale_stime(stime, rtime, stime + utime);
+		goto update;
 	}
 
+	stime = scale_stime(stime, rtime, stime + utime);
+
+update:
 	/*
 	 * Make sure stime doesn't go backwards; this preserves monotonicity
 	 * for utime because rtime is monotonic.