On Thu, Jan 23, 2014 at 11:49 AM, Hans Petter Selasky <
hans.petter.sela...@bitfrost.no> wrote:

>  Hi,
> Can you see if you can snap some keywords of the backtraces, like usb_xxx 
> usbdx_xxx cam scsi or something like that.
> Else I believe there are some sysctl options to prevent the final reboot 
> somehow so that you can write down the messages.
> --HPS
> -----Original message-----
> > From:Thomas Hoffmann <trh...@gmail.com>
> > Sent: Thursday 23rd January 2014 17:15
> > To: freebsd-current <freebsd-current@freebsd.org>
> > Subject: lock order reversals w/ backtrace
> >
> > A few days ago I started running 11.0-CURRENT at r260971 for the first time.
> >
> > The last couple of times I shutdown my system I noticed 2 or 3 short "lock
> > order reversal" messages with accompanying backtraces scroll by. Do these
> > messages represent a problem that I should report or can I ignore them as
> > debug in nature? If I should report them, how or where do these messages
> > get logged? I can find no reference to them in syslog or anywhere else upon
> > my subsequent reboot.
> >
> > I also had a couple of these messages pop up the other day while
> > mounting/umounting USB thumb drives. I did not think anything of them at
> > the time as the mounts/umounts completed successfully.
> >
> > Please advise. Thanks.
> >
> > -Tom
> I managed to snap a photo of my screen during shutdown.
Here is the full text of the first of two lock order reversals I got last
night during system shutdown, both of which are zfs-related to (it
appears?) unmounts. A few lines got chopped as they were out-of-frame when
I took the photo:

shutting down local daemons:
lock order reversal:
  1st 0xfffff801194f67c8 zfs (zfs) @ /usr/src/sys/kern/vfs_mount.c:1237
  2nd 0xfffff801194f6420 syncer (syncer) @
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_delf_wrapper+0x2b/frame
kdb_backtrace() at kdb_backtrace+0x39/frame 0xfffffe01ac784650
witness_checkorder() at witness_checkorder+0xd23/frame 0xfffffe01ac7846e0
__lockmgr_args() __lockmgr_args+0x878/frame 0xfffffe01ac784810
vop_stdlock() at vop_stdlock+0x3c/frame 0xfffffe01ac784830
VOP_LOCK1_APV() at VOP_LOCK1_APV+0xf5/frame 0xfffffe01ac784860
_vn_lock() at _vn_lock+0xab/frame 0xfffffe01ac7848d0
vputx() at vputx+0x240/frame 0xfffffe01ac784930
dounmount at dounmount+0x327/frame 0xfffffe01ac7849b0
sys_unmount() at sys_unmount+0x356/frame 0xfffffe01ac784ac0
amd64_syscall() at amd64_syscall+0x265/frame 0xfffffe01ac784bf0
Xfast_syscall() at Xfast_syscall+0xfb/frame 0xfffffe01ac784bf0
--- syscall (22, FreeBSD ELF64, sys_unmount, rip = 0x80191c72a,

I have a zpool on an external USB HDD that I export at shutdown via
rc.shutdown.local. Don't know if that is contributing to this or not. When
I get a chance to bring down the system I will manually export it before
shutdown to see if that makes any difference.
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