[PATCH] powerpc: Don't allocate zero bytes in finish_device_tree()

In prom.c we run finish_node() on allnodes twice. The first time we just
calculate how much memory we'll need, the second time we do the actual work.

If the calculation stage determines that we need 0 bytes, then we should skip
the lmb allocation. Although an alloc of zero will work, it has been seen to
lead to a BUG_ON() in reserve_bootmem() on at least one machine.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/kernel/prom.c

@@ -491,7 +491,12 @@ void __init finish_device_tree(void)
 	size = 16;
 	finish_node(allnodes, &size, 1);
 	size -= 16;
-	end = start = (unsigned long) __va(lmb_alloc(size, 128));
+
+	if (0 == size)
+		end = start = 0;
+	else
+		end = start = (unsigned long)__va(lmb_alloc(size, 128));
+
 	finish_node(allnodes, &end, 0);
 	BUG_ON(end != start + size);