[PATCH] mm: page_alloc: fix cma pageblock was stolen in rmqueue fallback

Lecopzer Chen
2023-08-30T19:17:31Z

commit 4b23a68f9536 ("mm/page_alloc: protect PCP lists with a
spinlock") fallback freeing page to free_one_page() if pcp trylock
failed. This make MIGRATE_CMA be able to fallback and be stolen
whole pageblock by MIGRATE_UNMOVABLE in the page allocation.

PCP free is fine because free_pcppages_bulk() will always get
migratetype again before freeing the page, thus this only happen when
someone tried to put CMA page in to other MIGRATE_TYPE's freelist.

Fixes: 4b23a68f9536 ("mm/page_alloc: protect PCP lists with a spinlock")
Reported-by: Joe Liu <joe.liu@mediatek.com>
Signed-off-by: Lecopzer Chen <lecopzer.chen@mediatek.com>
Cc: Mark-pk Tsai <mark-pk.tsai@mediatek.com>
Cc: Joe Liu <joe.liu@mediatek.com>
---
mm/page_alloc.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 452459836b71..0ea88c031838 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2428,6 +2428,14 @@ void free_unref_page(struct page *page, unsigned int order)
free_unref_page_commit(zone, pcp, page, migratetype, order);
pcp_spin_unlock(pcp);
} else {
+#ifdef CONFIG_CMA
+ /*
+ * CMA must be back to its freelist. Otherwise CMA pageblock may
+ * be stolen by fallback flow while getting free page.
+ */
+ if (get_pcppage_migratetype(page) == MIGRATE_CMA)
+ migratetype = MIGRATE_CMA;
+#endif
free_one_page(zone, page, pfn, order, migratetype, FPI_NONE);
}
pcp_trylock_finish(UP_flags);
--
2.18.0