In split_large_buddy(), we might call pfn_to_page() on a PFN that might
not exist. In corner cases, such as when freeing the highest pageblock in
the last memory section, this could result with CONFIG_SPARSEMEM &&
!CONFIG_SPARSEMEM_EXTREME in __pfn_to_section() returning NULL and
and __section_mem_map_addr() dereferencing that NULL pointer.
Let's fix it, and avoid doing a pfn_to_page() call for the first
iteration, where we already have the page.
So far this was found by code inspection, but let's just CC stable as
the fix is easy.
Fixes: fd919a85cd55 ("mm: page_isolation: prepare for hygienic freelists")
Reported-by: Vlastimil Babka <vbabka@xxxxxxx>
Closes: https://lkml.kernel.org/r/e1a898ba-a717-4d20-9144-29df1a6c8813@xxxxxxx
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
mm/page_alloc.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 48a291c485df4..a52c6022c65cb 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1238,13 +1238,15 @@ static void split_large_buddy(struct zone *zone, struct page *page,
if (order > pageblock_order)
order = pageblock_order;
- while (pfn != end) {
+ do {
int mt = get_pfnblock_migratetype(page, pfn);
__free_one_page(page, pfn, zone, order, mt, fpi);
pfn += 1 << order;
+ if (pfn == end)
+ break;
page = pfn_to_page(pfn);
- }
+ } while (1);
}
static void free_one_page(struct zone *zone, struct page *page,
--
2.47.1
