sched/uclamp: Reject negative values in cpu_uclamp_write()

The check to ensure that the new written value into cpu.uclamp.{min,max}
is within range, [0:100], wasn't working because of the signed
comparison

 7301                 if (req.percent > UCLAMP_PERCENT_SCALE) {
 7302                         req.ret = -ERANGE;
 7303                         return req;
 7304                 }

	# echo -1 > cpu.uclamp.min
	# cat cpu.uclamp.min
	42949671.96

Cast req.percent into u64 to force the comparison to be unsigned and
work as intended in capacity_from_percent().

	# echo -1 > cpu.uclamp.min
	sh: write error: Numerical result out of range

Fixes: 2480c09 ("sched/uclamp: Extend CPU's cgroup controller")
Signed-off-by: Qais Yousef <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

Author: Qais Yousef

kernel/sched/core.c

@@ -7264,7 +7264,7 @@ capacity_from_percent(char *buf)
 					     &req.percent);
 		if (req.ret)
 			return req;
-		if (req.percent > UCLAMP_PERCENT_SCALE) {
+		if ((u64)req.percent > UCLAMP_PERCENT_SCALE) {
 			req.ret = -ERANGE;
 			return req;
 		}