Sep 28 19:47:46 kernel: lock order reversal: Sep 28 19:47:46 kernel: 1st 0xffffff0002a9a308 ufs (ufs) @ /usr/src/ sys/kern/vfs_mount.c:1200 Sep 28 19:47:46 kernel: 2nd 0xffffff0002a63a58 devfs (devfs) @ /usr/ src/sys/ufs/ffs/ffs_vfsops.c:1194 Sep 28 19:47:46 kernel: KDB: stack backtrace: Sep 28 19:47:46 kernel: db_trace_self_wrapper() at db_trace_self_wrapper+0x2a Sep 28 19:47:46 kernel: _witness_debugger() at _witness_debugger+0x2e Sep 28 19:47:46 kernel: witness_checkorder() at witness_checkorder +0x81e Sep 28 19:47:46 kernel: __lockmgr_args() at __lockmgr_args+0xd03 Sep 28 19:47:46 kernel: vop_stdlock() at vop_stdlock+0x39 Sep 28 19:47:46 kernel: VOP_LOCK1_APV() at VOP_LOCK1_APV+0x9b Sep 28 19:47:46 kernel: _vn_lock() at _vn_lock+0x57 Sep 28 19:47:46 kernel: ffs_flushfiles() at ffs_flushfiles+0xc5 Sep 28 19:47:46 kernel: softdep_flushfiles() at softdep_flushfiles+0x63 Sep 28 19:47:46 kernel: ffs_unmount() at ffs_unmount+0x2e1 Sep 28 19:47:46 kernel: dounmount() at dounmount+0x2e6 Sep 28 19:47:46 kernel: unmount() at unmount+0x27e Sep 28 19:47:46 kernel: syscall() at syscall+0x1d0 Sep 28 19:47:46 kernel: Xfast_syscall() at Xfast_syscall+0xe1 Sep 28 19:47:46 kernel: --- syscall (22, FreeBSD ELF64, unmount), rip = 0x8006a09bc, rsp = 0x7fffffffe3b8, rbp = 0 --- FreeBSD 8.0-RC1 FreeBSD 8.0-RC1 #0: Fri Sep 25 16:55:06 CEST 2009 root@:/usr/obj/usr/src/sys/DEBUG amd64 I'm running it on VMWare Fussion, but it shouldn't matter. The system has two disks, one of them just a root partition and the other one has two filesystems, one for /usr/src and the other for /usr/ obj How to reproduce? Right after boot, I have mounted /usr/src and /usr/obj. Unmounting /usr/obj has given this LOR. I can reproduce it easily, please let me know if I can do anything else. Borja.