[PATCH 5.14 408/432] mm/page_alloc.c: avoid accessing uninitialized pcp page migratetype

From: Miaohe Lin <linmiaohe@huawei.com>

commit 053cfda102306a3394012f9fe2594811c34925e4 upstream.

If it's not prepared to free unref page, the pcp page migratetype is
unset.  Thus we will get rubbish from get_pcppage_migratetype() and
might list_del(&page->lru) again after it's already deleted from the list
leading to grumble about data corruption.

Link: https://lkml.kernel.org/r/20210902115447.57050-1-linmiaohe@huawei.com
Fixes: df1acc856923 ("mm/page_alloc: avoid conflating IRQs disabled with zone->lock")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Acked-by: Mel Gorman <redacted>
Acked-by: Vlastimil Babka <redacted>
Reviewed-by: David Hildenbrand <redacted>
Cc: <redacted>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 mm/page_alloc.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c

@@ -3445,8 +3445,10 @@ void free_unref_page_list(struct list_he
 	/* Prepare pages for freeing */
 	list_for_each_entry_safe(page, next, list, lru) {
 		pfn = page_to_pfn(page);
-		if (!free_unref_page_prepare(page, pfn, 0))
+		if (!free_unref_page_prepare(page, pfn, 0)) {
 			list_del(&page->lru);
+			continue;
+		}
 
 		/*
 		 * Free isolated pages directly to the allocator, see