[PATCH] mm: stricter check on THP migration entry

[Miaohe Lin <linmiaohe@huawei.com>]

When VM_BUG_ON check for THP migration entry, the existing code only check
thp_migration_supported case, but not for !thp_migration_supported case.
If !thp_migration_supported() and !pmd_present(), the original code may
dead loop in theory.  To make the VM_BUG_ON check more consistent, we need
to catch both cases.

Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 mm/memory.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index fee2884481f2..6a9a17c7f58a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5043,10 +5043,9 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
 
 		barrier();
 		if (unlikely(is_swap_pmd(vmf.orig_pmd))) {
-			VM_BUG_ON(thp_migration_supported() &&
-					  !is_pmd_migration_entry(vmf.orig_pmd));
-			if (is_pmd_migration_entry(vmf.orig_pmd))
-				pmd_migration_entry_wait(mm, vmf.pmd);
+			VM_BUG_ON(!thp_migration_supported() ||
+				  !is_pmd_migration_entry(vmf.orig_pmd));
+			pmd_migration_entry_wait(mm, vmf.pmd);
 			return 0;
 		}
 		if (pmd_trans_huge(vmf.orig_pmd) || pmd_devmap(vmf.orig_pmd)) {
-- 
2.23.0