System hang on shutdown when running freebsd-update

[Jilles Tjoelker]

On Wed, Dec 10, 2014 at 09:48:18PM +0100, Walter Hop wrote:
> root at current:~ # chflags noschg /sbin/init
> root at current:~ # cp -Rp /sbin/init /sbin/init2
> lock order reversal:
> 1st 0xfffffe007b842fa0 bufwait (bufwait) @ /usr/src/sys/kern/vfs_bio.c:3093
> 2nd 0xfffff80002b9ea00 dirhash (dirhash) @ /usr/src/sys/ufs/ufs/ufs_dirhash.c:284
> KDB: stack backtrace:
> db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe000025c270
> kdb_backtrace() at kdb_backtrace+0x39/frame 0xfffffe000025c320
> witness_checkorder() at witness_checkorder+0xdad/frame 0xfffffe000025c3b0
> _sx_xlock() at _sx_xlock+0x75/frame 0xfffffe000025c3f0
> ufsdirhash_add() at ufsdirhash_add+0x3a/frame 0xfffffe000025c430
> ufs_direnter() at ufs_direnter+0x6a0/frame 0xfffffe000025c4f0
> ufs_makeinode() at ufs_makeinode+0x560/frame 0xfffffe000025c6a0
> VOP_CREATE_APV() at VOP_CREATE_APV+0xf1/frame 0xfffffe000025c6d0
> vn_open_cred() at vn_open_cred+0x29d/frame 0xfffffe000025c820
> kern_openat() at kern_openat+0x26f/frame 0xfffffe000025c9a0
> amd64_syscall() at amd64_syscall+0x25a/frame 0xfffffe000025cab0
> Xfast_syscall() at Xfast_syscall+0xfb/frame 0xfffffe000025cab0
> --- syscall (5, FreeBSD ELF64, sys_open), rip = 0x80094f01a, rsp = 0x7fffffffe958, rbp = 0x7fffffffe9c0 ---

> Screenshot is here: http://lf.ms/current-r273635-hang-1.png <http://lf.ms/current-r273635-hang-1.png>

> Finally, when rebooting, another lock order reversal appears and the
> system hangs. I don’t have a text log of this, so I’ll copy the first
> few lines:

> Syncing disks, vnodes remaining…1 0 0 done
> All buffers synced.
> lock order reversal:
>  1st 0xfffff80002e65d50 ufs (ufs) @ /usr/src/sys/kern/vfs_mount.c:1223
>  2nd 0xfffff80002e665f0 devfs (devfs) @ /usr/src/sys/kern/vfs_subr.c:2144

> Screenshot is here: http://lf.ms/current-r273635-hang-2.png <http://lf.ms/current-r273635-hang-2.png>

> I don’t have kernel hacking experience, but these source files look
> awfully related to the parts that we are having problems with.

> I would really love some research into this and possibly an errata for
> 10.1. What can we do to make this actionable?

Both of these LORs are false positives. There is no mechanism in WITNESS
to suppress them properly.

I cannot reproduce the problem (VirtualBox, stable/10 amd64 and head
i386), so apparently there is something special about some users'
environments that causes this.

-- 
Jilles Tjoelker