mm/page_alloc: don't corrupt pcppage_migratetype

When placing pages on a pcp list, migratetype values over
MIGRATE_PCPTYPES get added to the MIGRATE_MOVABLE pcp list.

However, the actual migratetype is preserved in the page and should
not be changed to MIGRATE_MOVABLE or the page may end up on the wrong
free_list.

The impact is that HIGHATOMIC or CMA pages getting bulk freed from the
PCP lists could potentially end up on the wrong buddy list.  There are
various consequences but minimally NR_FREE_CMA_PAGES accounting could
get screwed up.

[mgorman@techsingularity.net: changelog update]

Link: https://lkml.kernel.org/r/20210811182917.2607994-1-opendmb@gmail.com
Fixes: df1acc8 ("mm/page_alloc: avoid conflating IRQs disabled with zone->lock")
Signed-off-by: Doug Berger <opendmb@gmail.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_alloc.c

@@ -3453,19 +3453,10 @@ void free_unref_page_list(struct list_head *list)
 		 * comment in free_unref_page.
 		 */
 		migratetype = get_pcppage_migratetype(page);
-		if (unlikely(migratetype >= MIGRATE_PCPTYPES)) {
-			if (unlikely(is_migrate_isolate(migratetype))) {
-				list_del(&page->lru);
-				free_one_page(page_zone(page), page, pfn, 0,
-							migratetype, FPI_NONE);
-				continue;
-			}
-
-			/*
-			 * Non-isolated types over MIGRATE_PCPTYPES get added
-			 * to the MIGRATE_MOVABLE pcp list.
-			 */
-			set_pcppage_migratetype(page, MIGRATE_MOVABLE);
+		if (unlikely(is_migrate_isolate(migratetype))) {
+			list_del(&page->lru);
+			free_one_page(page_zone(page), page, pfn, 0, migratetype, FPI_NONE);
+			continue;
 		}
 
 		set_page_private(page, pfn);
@@ -3475,7 +3466,15 @@ void free_unref_page_list(struct list_head *list)
 	list_for_each_entry_safe(page, next, list, lru) {
 		pfn = page_private(page);
 		set_page_private(page, 0);
+
+		/*
+		 * Non-isolated types over MIGRATE_PCPTYPES get added
+		 * to the MIGRATE_MOVABLE pcp list.
+		 */
 		migratetype = get_pcppage_migratetype(page);
+		if (unlikely(migratetype >= MIGRATE_PCPTYPES))
+			migratetype = MIGRATE_MOVABLE;
+
 		trace_mm_page_free_batched(page);
 		free_unref_page_commit(page, pfn, migratetype, 0);