It's dangerous and wrong to call page_folio(pmd_page(*pmd)) when pmd isn't
present. But the caller guarantees pmd is present when folio is set. So we
should be safe here. Add comment to make it clear.
Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
---
mm/huge_memory.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 36f3fc2e7306..8380912b39fd 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2336,6 +2336,10 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd) ||
is_pmd_migration_entry(*pmd)) {
+ /*
+ * It's safe to call pmd_page when folio is set because it's
+ * guaranteed that pmd is present.
+ */
if (folio && folio != page_folio(pmd_page(*pmd)))
goto out;
__split_huge_pmd_locked(vma, pmd, range.start, freeze);
--
2.23.0
