4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ard Biesheuvel <ard.biesheu...@linaro.org>


[ Upstream commit f073bdc51771f5a5c7a8d1191bfc3ae371d44de7 ]

The VM_BUG_ON() check in move_freepages() checks whether the node id of
a page matches the node id of its zone.  However, it does this before
having checked whether the struct page pointer refers to a valid struct
page to begin with.  This is guaranteed in most cases, but may not be
the case if CONFIG_HOLES_IN_ZONE=y.

So reorder the VM_BUG_ON() with the pfn_valid_within() check.

Link: 
http://lkml.kernel.org/r/1481706707-6211-2-git-send-email-ard.biesheu...@linaro.org
Signed-off-by: Ard Biesheuvel <ard.biesheu...@linaro.org>
Acked-by: Will Deacon <will.dea...@arm.com>
Cc: Catalin Marinas <catalin.mari...@arm.com>
Cc: Hanjun Guo <hanjun....@linaro.org>
Cc: Yisheng Xie <xieyishe...@huawei.com>
Cc: Robert Richter <rrich...@cavium.com>
Cc: James Morse <james.mo...@arm.com>
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Sasha Levin <alexander.le...@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 mm/page_alloc.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1875,14 +1875,14 @@ int move_freepages(struct zone *zone,
 #endif
 
        for (page = start_page; page <= end_page;) {
-               /* Make sure we are not inadvertently changing nodes */
-               VM_BUG_ON_PAGE(page_to_nid(page) != zone_to_nid(zone), page);
-
                if (!pfn_valid_within(page_to_pfn(page))) {
                        page++;
                        continue;
                }
 
+               /* Make sure we are not inadvertently changing nodes */
+               VM_BUG_ON_PAGE(page_to_nid(page) != zone_to_nid(zone), page);
+
                if (!PageBuddy(page)) {
                        page++;
                        continue;


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