linux-kernel - [PATCH] mm/page_alloc: don't corrupt pcppage

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Date:   Wed, 11 Aug 2021 11:29:17 -0700
From:   Doug Berger <opendmb@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Doug Berger <opendmb@...il.com>
Subject: [PATCH] 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.

Fixes: df1acc856923 ("mm/page_alloc: avoid conflating IRQs disabled with zone->lock")
Signed-off-by: Doug Berger <opendmb@...il.com>
---
 mm/page_alloc.c | 25 ++++++++++++-------------
 1 file changed, 12 insertions(+), 13 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 73704e836649..8addb4919f75 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3436,19 +3436,10 @@ 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);
@@ -3458,7 +3449,15 @@ 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);
 
-- 
2.25.1