[PATCH] mm/migrate_device: fix double unlock and remove dead code

Sunny Patel
2026-04-13T13:09:42Z

Fix two bugs in device migration paths:

1) migrate_vma_collect_huge_pmd() calls spin_unlock after
softleaf_entry_wait_on_locked(), which already releases the ptl.

2) migrate_vma_insert_huge_pmd_page() has a dead else-if branch and this
branch is always unreachable.

Signed-off-by: Sunny Patel <nueralspacetech@gmail.com>
---
mm/migrate_device.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/mm/migrate_device.c b/mm/migrate_device.c
index 8079676c8f1f..0e005c26ee88 100644
--- a/mm/migrate_device.c
+++ b/mm/migrate_device.c
@@ -177,7 +177,6 @@ static int migrate_vma_collect_huge_pmd(pmd_t *pmdp, unsigned long start,

if (softleaf_is_migration(entry)) {
softleaf_entry_wait_on_locked(entry, ptl);
- spin_unlock(ptl);
return -EAGAIN;
}

@@ -869,8 +868,7 @@ static int migrate_vma_insert_huge_pmd_page(struct migrate_vma *migrate,
if (!is_huge_zero_pmd(*pmdp))
goto unlock_abort;
flush = true;
- } else if (!pmd_none(*pmdp))
- goto unlock_abort;
+ }

add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
folio_add_new_anon_rmap(folio, vma, addr, RMAP_EXCLUSIVE);
--
2.43.0