fault-inject: avoid call to random32() if fault injection is disabled

After enabling CONFIG_FAILSLAB I noticed random32 in profiles even if slub
fault injection wasn't enabled at runtime.

should_fail forces a comparison against random32() even if probability is
0:

if (attr->probability <= random32() % 100)
return false;

Add a check up front for probability == 0 and avoid all of the more
complicated checks.

Signed-off-by: Anton Blanchard <[e-mail]>
Acked-by: Akinobu Mita <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

lib/fault-inject.c

···
 
 bool should_fail(struct fault_attr *attr, ssize_t size)
 {
+	/* No need to check any other properties if the probability is 0 */
+	if (attr->probability == 0)
+		return false;
+
 	if (attr->task_filter && !fail_task(attr, current))
 		return false;