kernel/resource.c: handle reinsertion of an already-inserted resource

If the same resource is inserted to the resource tree (maybe not on
purpose), a dead loop will be created. In this situation, The kernel does
not report any warning or error :(

The command below will show a endless print.
#cat /proc/iomem

[[e-mail]: add WARN_ON()]
Signed-off-by: Huang Shijie <[e-mail]>
Cc: Jesse Barnes <[e-mail]>
Cc: Bjorn Helgaas <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

kernel/resource.c

···
 
 		if (first == parent)
 			return first;
+		if (WARN_ON(first == new))	/* duplicated insertion */
+			return first;
 
 		if ((first->start > new->start) || (first->end < new->end))
 			break;