Panic on todays current (panic: mtx_lock() of spin mutex (null) _at_ /usr/src/sys/kern/vfs_mount.c:1046)

Hello. I've got this while booting:

Starting file system checks:
/dev/ad0s4a: FILE SYSTEM CLEAN; SKIPPING CHECKS
/dev/ad0s4a: clean, 6113 free (241 frags, 734 blocks, 0.2% fragmentation)
/dev/ad0s4f: FILE SYSTEM CLEAN; SKIPPING CHECKS
/dev/ad0s4f: clean, 67511 free (2623 frags, 8111 blocks, 0.4% 
fragmentation)
/dev/ad0s4e.journal: FILE SYSTEM CLEAN; SKIPPING CHECKS
Setting hostuuid: 44454C4C-4400-1039-8030-B6C04F4A324A.
Setting hostid: 0x7817d87e.
Mounting local file systems:
panic: mtx_lock() of spin mutex (null) _at_ /usr/src/sys/kern/vfs_mount.c:1046
cpuid = 0
KDB: enter: panic
exclusive sleep mutex Giant r = 0 (0xc0ba7350) locked 
_at_ /usr/src/sys/kern/kern_module.c:117
panic: from debugger
cpuid = 0
Uptime: 6s
Physical memory: 1003 MB
Dumping 47 MB: 32 16

#0  doadump () at pcpu.h:195
195             __asm __volatile("movl %%fs:0,%0" : "=r" (td));
(kgdb) bt
#0  doadump () at pcpu.h:195
#1  0xc074c19e in boot (howto=260) at /usr/src/sys/kern/kern_shutdown.c:409
#2  0xc074c45b in panic (fmt=Variable "fmt" is not available.
) at /usr/src/sys/kern/kern_shutdown.c:563
#3  0xc048c6d7 in db_panic (addr=Could not find the frame base 
for "db_panic".
) at /usr/src/sys/ddb/db_command.c:433
#4  0xc048d0c5 in db_command_loop () at /usr/src/sys/ddb/db_command.c:401
#5  0xc048e835 in db_trap (type=3, code=0) 
at /usr/src/sys/ddb/db_main.c:222
#6  0xc07730c6 in kdb_trap (type=3, code=0, tf=0xe46959f0) 
at /usr/src/sys/kern/subr_kdb.c:502
#7  0xc09fd25b in trap (frame=0xe46959f0) 
at /usr/src/sys/i386/i386/trap.c:621
#8  0xc09e2c8b in calltrap () at /usr/src/sys/i386/i386/exception.s:139
#9  0xc0773242 in kdb_enter (msg=0xc0a93513 "panic") at cpufunc.h:60
#10 0xc074c444 in panic (fmt=0xc0a92475 "mtx_lock() of spin mutex %s _at_ %s:
%d") at /usr/src/sys/kern/kern_shutdown.c:547
#11 0xc0740d3a in _mtx_lock_flags (m=0xc42b0000, opts=0, 
file=0xc0a9e111 "/usr/src/sys/kern/vfs_mount.c", line=1046) 
at /usr/src/sys/kern/kern_mutex.c:180
#12 0xc07c154b in vfs_donmount (td=0xc429f800, fsflags=0, 
fsoptions=0xc431ce00) at /usr/src/sys/kern/vfs_mount.c:1046
#13 0xc07c25e3 in nmount (td=0xc429f800, uap=0xe4695cfc) 
at /usr/src/sys/kern/vfs_mount.c:413
#14 0xc09fca13 in syscall (frame=0xe4695d38) 
at /usr/src/sys/i386/i386/trap.c:1008
#15 0xc09e2cf0 in Xint0x80_syscall () 
at /usr/src/sys/i386/i386/exception.s:196
#16 0x00000033 in ?? ()
Previous frame inner to this frame (corrupt stack?)



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* Best regards, Nikolay Pavlov *