[PATCH] drivers/base/memory.c: Fix "mm/memory_hotplug: Move and simplify walk_memory_blocks()"

[David Hildenbrand]

The start and the size are 0 for online nodes without any memory. Avoid
the underflow, resulting in a very long loop and soft lockups.

Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Reported-by: Qian Cai <cai@xxxxxx>
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---

@Andrew, Stephen - sorry for the noise *again*. Feel feel to either apply
this patch or drop the respective patches for now.

---
 drivers/base/memory.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index 972c5336bebf..7595a4f0068f 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -868,6 +868,9 @@ int walk_memory_blocks(unsigned long start, unsigned long size,
 	unsigned long block_id;
 	int ret = 0;
 
+	if (!size)
+		return 0;
+
 	for (block_id = start_block_id; block_id <= end_block_id; block_id++) {
 		mem = find_memory_block_by_id(block_id);
 		if (!mem)
-- 
2.21.0