mm: hugetlb: fix missing put_page in gather_surplus_pages()

The VM_BUG_ON_PAGE avoids the generation of any code, even if that
expression has side-effects when !CONFIG_DEBUG_VM.

Link: https://lkml.kernel.org/r/20210126031009.96266-1-songmuchun@bytedance.com
Fixes: e5dfaceb ("mm/hugetlb.c: just use put_page_testzero() instead of page_count()")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/hugetlb.c

@@ -2047,13 +2047,16 @@ static int gather_surplus_pages(struct hstate *h, long delta)
 
 	/* Free the needed pages to the hugetlb pool */
 	list_for_each_entry_safe(page, tmp, &surplus_list, lru) {
+		int zeroed;
+
 		if ((--needed) < 0)
 			break;
 		/*
 		 * This page is now managed by the hugetlb allocator and has
 		 * no users -- drop the buddy allocator's reference.
 		 */
-		VM_BUG_ON_PAGE(!put_page_testzero(page), page);
+		zeroed = put_page_testzero(page);
+		VM_BUG_ON_PAGE(!zeroed, page);
 		enqueue_huge_page(h, page);
 	}
 free: