[PATCH] mm/hugetlb: copy the CMA flag when demoting

[Frank van der Linden <fvdl@google.com>]

Since commit d2d786714080 ("mm/hugetlb: enable bootmem allocation
from CMA areas"), a flag is used to mark hugetlb folios as allocated
from CMA. This flag is also used to decide if it should be freed
to CMA.

However, the flag isn't copied to the smaller folios when a hugetlb
folio is broken up for demotion, which would cause it to be freed
incorrectly.

Fix this by copying the flag to the smaller order hugetlb pages
created from the original one.

Fixes: d2d786714080 ("mm/hugetlb: enable bootmem allocation from CMA areas")
Signed-off-by: Frank van der Linden <fvdl@google.com>
---
 mm/hugetlb.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index e3e6ac991b9c..6ea1be71aa42 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4034,10 +4034,13 @@ static long demote_free_hugetlb_folios(struct hstate *src, struct hstate *dst,
 
 	list_for_each_entry_safe(folio, next, src_list, lru) {
 		int i;
+		bool cma;
 
 		if (folio_test_hugetlb_vmemmap_optimized(folio))
 			continue;
 
+		cma = folio_test_hugetlb_cma(folio);
+
 		list_del(&folio->lru);
 
 		split_page_owner(&folio->page, huge_page_order(src), huge_page_order(dst));
@@ -4053,6 +4056,9 @@ static long demote_free_hugetlb_folios(struct hstate *src, struct hstate *dst,
 
 			new_folio->mapping = NULL;
 			init_new_hugetlb_folio(dst, new_folio);
+			/* Copy the CMA flag so that it is freed correctly */
+			if (cma)
+				folio_set_hugetlb_cma(new_folio);
 			list_add(&new_folio->lru, &dst_list);
 		}
 	}
-- 
2.49.0.967.g6a0df3ecc3-goog