mm: wrap __find_buddy_pfn() with a necessary buddy page validation

Whenever the buddy of a page is found from __find_buddy_pfn(),
page_is_buddy() should be used to check its validity.  Add a helper
function find_buddy_page_pfn() to find the buddy page and do the check
together.

[ziy@nvidia.com: updates per David]
Link: https://lkml.kernel.org/r/20220401230804.1658207-2-zi.yan@sent.com
Link: https://lore.kernel.org/linux-mm/CAHk-=wji_AmYygZMTsPMdJ7XksMt7kOur8oDfDdniBRMjm4VkQ@mail.gmail.com/
Link: https://lkml.kernel.org/r/7236E7CA-B5F1-4C04-AB85-E86FA3E9A54B@nvidia.com
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Zi Yan <ziy@nvidia.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 8 insertions, 44 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 26dea6cd3f53..8de8d7a5c3e3 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -867,40 +867,6 @@ static inline void set_buddy_order(struct page *page, unsigned int order)
 	__SetPageBuddy(page);
 }
 
-/*
- * This function checks whether a page is free && is the buddy
- * we can coalesce a page and its buddy if
- * (a) the buddy is not in a hole (check before calling!) &&
- * (b) the buddy is in the buddy system &&
- * (c) a page and its buddy have the same order &&
- * (d) a page and its buddy are in the same zone.
- *
- * For recording whether a page is in the buddy system, we set PageBuddy.
- * Setting, clearing, and testing PageBuddy is serialized by zone->lock.
- *
- * For recording page's order, we use page_private(page).
- */
-static inline bool page_is_buddy(struct page *page, struct page *buddy,
-							unsigned int order)
-{
-	if (!page_is_guard(buddy) && !PageBuddy(buddy))
-		return false;
-
-	if (buddy_order(buddy) != order)
-		return false;
-
-	/*
-	 * zone check is done late to avoid uselessly calculating
-	 * zone/node ids for pages that could never merge.
-	 */
-	if (page_zone_id(page) != page_zone_id(buddy))
-		return false;
-
-	VM_BUG_ON_PAGE(page_count(buddy) != 0, buddy);
-
-	return true;
-}
-
 #ifdef CONFIG_COMPACTION
 static inline struct capture_control *task_capc(struct zone *zone)
 {
@@ -1009,18 +975,17 @@ static inline bool
 buddy_merge_likely(unsigned long pfn, unsigned long buddy_pfn,
 		   struct page *page, unsigned int order)
 {
-	struct page *higher_page, *higher_buddy;
-	unsigned long combined_pfn;
+	unsigned long higher_page_pfn;
+	struct page *higher_page;
 
 	if (order >= MAX_ORDER - 2)
 		return false;
 
-	combined_pfn = buddy_pfn & pfn;
-	higher_page = page + (combined_pfn - pfn);
-	buddy_pfn = __find_buddy_pfn(combined_pfn, order + 1);
-	higher_buddy = higher_page + (buddy_pfn - combined_pfn);
+	higher_page_pfn = buddy_pfn & pfn;
+	higher_page = page + (higher_page_pfn - pfn);
 
-	return page_is_buddy(higher_page, higher_buddy, order + 1);
+	return find_buddy_page_pfn(higher_page, higher_page_pfn, order + 1,
+			NULL) != NULL;
 }
 
 /*
@@ -1074,10 +1039,9 @@ static inline void __free_one_page(struct page *page,
 								migratetype);
 			return;
 		}
-		buddy_pfn = __find_buddy_pfn(pfn, order);
-		buddy = page + (buddy_pfn - pfn);
 
-		if (!page_is_buddy(page, buddy, order))
+		buddy = find_buddy_page_pfn(page, pfn, order, &buddy_pfn);
+		if (!buddy)
 			goto done_merging;
 
 		if (unlikely(order >= pageblock_order)) {