[PATCH 2/3] mm/hugetlb: preserve CMA flag when returning folios to the pool

[Kaitao Cheng <kaitao.cheng@linux.dev>]

From: Kaitao Cheng <chengkaitao@kylinos.cn>

When vmemmap restoration fails, add_hugetlb_folio() returns the folio
to the hugetlb pool. It clears folio->private and restores only
HPG_vmemmap_optimized, losing HPG_cma on CMA-allocated folios.

A later successful free then bypasses hugetlb_cma_free_frozen_folio()
and returns the pages through free_frozen_pages(). The CMA allocation
bitmap remains set, so the range is unavailable for future CMA
allocations.

Save the CMA flag before resetting folio->private and restore it along
with the vmemmap optimization flag.

Fixes: d2d786714080 ("mm/hugetlb: enable bootmem allocation from CMA areas")
Closes: https://sashiko.dev/#/bug/linux-5363eb09-9c3c-4f8b-9f3c-a998a8c4b258
Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>
---
 mm/hugetlb.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 4a008afaedf9..8da4bab676c9 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1437,6 +1437,7 @@ void remove_hugetlb_folio(struct hstate *h, struct folio *folio,
 void add_hugetlb_folio(struct hstate *h, struct folio *folio,
 		       bool adjust_surplus)
 {
+	bool cma = folio_test_hugetlb_cma(folio);
 	int nid = folio_nid(folio);
 
 	VM_BUG_ON_FOLIO(!folio_test_hugetlb_vmemmap_optimized(folio), folio);
@@ -1453,9 +1454,11 @@ void add_hugetlb_folio(struct hstate *h, struct folio *folio,
 	}
 
 	__folio_set_hugetlb(folio);
-	/* Clear all folio->private flags except hugetlb_vmemmap_optimized. */
+	/* Preserve the vmemmap optimization state and CMA allocation origin. */
 	folio->private = NULL;
 	folio_set_hugetlb_vmemmap_optimized(folio);
+	if (cma)
+		folio_set_hugetlb_cma(folio);
 
 	arch_clear_hugetlb_flags(folio);
 	enqueue_hugetlb_folio(h, folio);
-- 
2.53.0