Hello, I've just checkedout stable/12 branch. Unmounting msdosfs blocks # newfs_msdos -C 40M efiboot.img efiboot.img: 81800 sectors in 10225 FAT16 clusters (4096 bytes/cluster) BytesPerSec=512 SecPerClust=8 ResSectors=1 FATs=2 RootDirEnts=512 Media=0xf0 FATsecs=40 SecPerTrack=63 Heads=255 HiddenSecs=0 HugeSectors=81920 # mdconfig ./efiboot.img md0 # mount -t msdosfs /dev/md0 /mnt # umount -vf /mnt (uninterruptable wait) On other termial: # ps ax | grep umount 1333 0 D+ 0:00.00 umount -vf /mnt There is not such a problem on 12.1 stable Thanks