$ uname -a
FreeBSD virt-bsd 12.0-CURRENT FreeBSD 12.0-CURRENT #0 r319667: Fri Jun  9 00:35:07 JST 2017     root@virt-bsd:/usr/src/sys/amd64/compile/fifth  amd64
$ df -h
Filesystem         Size    Used   Avail Capacity  Mounted on
/dev/gpt/rootfs     19G     16G    1.8G    90%    /
devfs              1.0K    1.0K      0B   100%    /dev
$ sudo growfs /
Device is mounted read-write; resizing will result in temporary write suspension for /.
It's strongly recommended to make a backup before growing the file system.
OK to grow filesystem on /dev/gpt/rootfs, mounted on /, from 20GB to 49GB? [yes/no] yes
lock order reversal:
 1st 0xfffff800027ced50 ufs (ufs) @ kern/vfs_subr.c:2602
 2nd 0xfffffe001de35050 bufwait (bufwait) @ ufs/ffs/ffs_vnops.c:280
 3rd 0xfffff8000299b9a0 ufs (ufs) @ kern/vfs_subr.c:2602
stack backtrace:
#0 0xffffffff807c81a0 at witness_debugger+0x70
#1 0xffffffff807c8093 at witness_checkorder+0xe23
#2 0xffffffff8073d325 at __lockmgr_args+0x875
#3 0xffffffff809f86e5 at ffs_lock+0xa5
#4 0xffffffff80c93530 at VOP_LOCK1_APV+0xe0
#5 0xffffffff8083edba at _vn_lock+0x6a
#6 0xffffffff8082dd52 at vget+0x82
#7 0xffffffff8082004c at vfs_hash_get+0xdc
#8 0xffffffff809f43ef at ffs_vgetf+0x3f
#9 0xffffffff809eaa49 at softdep_sync_buf+0xb89
#10 0xffffffff809f93f2 at ffs_syncvnode+0x292
#11 0xffffffff809f70cd at ffs_sync+0x3bd
#12 0xffffffff80840476 at vfs_write_suspend+0x176
#13 0xffffffff809fa806 at ffs_susp_ioctl+0x1b6
#14 0xffffffff80638960 at devfs_ioctl+0xc0
#15 0xffffffff80c92000 at VOP_IOCTL_APV+0xe0
#16 0xffffffff8083db34 at vn_ioctl+0x124
#17 0xffffffff80638fff at devfs_ioctl_f+0x1f
super-block backups (for fsck_ffs -b #) at:
 42314112, 43596352, 44878592, 46160832, 47443072, 48725312, 50007552,
 51289792, 52572032, 53854272, 55136512, 56418752, 57700992, 58983232,
 60265472, 61547712, 62829952, 64112192, 65394432, 66676672, 67958912,
 69241152, 70523392, 71805632, 73087872, 74370112, 75652352, 76934592,
 78216832, 79499072, 80781312, 82063552, 83345792, 84628032, 85910272,
 87192512, 88474752, 89756992, 91039232, 92321472, 93603712, 94885952,
 96168192, 97450432, 98732672, 100014912, 101297152, 102579392
WARNING: /: reload pending error: blocks 136 files 3
$ echo $?
0
$ df -h
Filesystem         Size    Used   Avail Capacity  Mounted on
/dev/gpt/rootfs     47G     16G     28G    37%    /
devfs              1.0K    1.0K      0B   100%    /dev