=== DF-5799 reproduction ===
DragonFly dfbsd 6.5-DEVELOPMENT DragonFly 6.5-DEVELOPMENT #1: Mon Oct 12 21:32:58 UTC 2026     root@dfbsd:/usr/obj/usr/src/sys/X86_64_GENERIC  x86_64
--- [1] primary hammer2 mount ---
mount rc=0
--- [2] PFS list ---
Type        ClusterId (pfs_clid)                 Label on /mnt/a
MASTER      7487e711-c685-11f1-bff1-010000000000 LOCAL
MASTER      7487e820-c685-11f1-bff1-010000000000 ROOT
--- [3] raw write gate BEFORE secondary mount (expect EBUSY) ---
dd: /dev/vn0: dd rc=1
--- [4] routine secondary PFS mount from the same device ---
Device busy
mount rc=0
/dev/vn0@ROOT on /mnt/a (hammer2, local)
/dev/vn0@LOCAL on /mnt/b (hammer2, local)
--- [5] raw write gate AFTER secondary mount (BUG: expect success) ---
dd: /dev/vn0: Device busy
dd rc=1
--- [6] also a FAILED secondary mount attempt strips the gate ---
mount_hammer2: /dev/vn0@NOSUCH not found
failed-mount rc=1 (expected nonzero)
dd: /dev/vn0: Device busy
dd rc=1
vnconfig: VNIOCDETACH: Device busy
--- [7] UFS mount on vn1 ---
ufs mount rc=0
--- raw write gate on UFS device (expect EBUSY) ---
dd rc=1
--- [8] failed hammer2 mount attempt over the UFS device ---
dd: /dev/vn1: Device busy
mount: Device busy
h2 mount rc=1 (expected 1: Device busy)
--- [9] raw write gate after failed attempt (BUG: expect success) ---
dd rc=1
dd: /dev/vn1: Device busy
=== done ===
vnconfig: VNIOCDETACH: Device busy