selftests: cgroup: fix unsigned comparison with less than zero

'size' is unsigned, it never less than zero.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 6c26df8 ("selftests: cgroup: return -errno from cg_read()/cg_write() on failure")
Signed-off-by: YueHaibing <[email protected]>
Reviewed-by: Yosry Ahmed <[email protected]>
Acked-by: Roman Gushchin <[email protected]>
Reviewed-by: Kamalesh Babulal <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Shakeel Butt <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: zefan li <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

tools/testing/selftests/cgroup/cgroup_util.c

@@ -555,15 +555,16 @@ int proc_mount_contains(const char *option)
 ssize_t proc_read_text(int pid, bool thread, const char *item, char *buf, size_t size)
 {
 	char path[PATH_MAX];
+	ssize_t ret;
 
 	if (!pid)
 		snprintf(path, sizeof(path), "/proc/%s/%s",
 			 thread ? "thread-self" : "self", item);
 	else
 		snprintf(path, sizeof(path), "/proc/%d/%s", pid, item);
 
-	size = read_text(path, buf, size);
-	return size < 0 ? -1 : size;
+	ret = read_text(path, buf, size);
+	return ret < 0 ? -1 : ret;
 }
 
 int proc_read_strstr(int pid, bool thread, const char *item, const char *needle)