panic: share -> excl _at_r224632

I've only seen this on my laptop; my build machine doesn't exhibit the
panic.

r224602 is the most recent point I've built that does not exhibit the
panic at all.

The first few lines (hand-transcribed; I have no serial console on this
laptop -- the one shortcoming it has):

shared lock of (lockmgr) devfs _at_/usr/src/sys/kern/vfs_cache.c:1116
while exclusively locked from /usr/src/sys/kern/vfs_subr.c:2134
panic: share -> excl

The backtrace (which I wasn't patient enough to trto transcribe twice;
sorry) appeared to involve "nmount", and the panic occurred directly
after mounting the file systems during the transition from single-user
mode to multi-user mode.

The output from "svn update" going from r224602 -> r224632 shows the
following files being updated:

U    usr.sbin/faithd/faithd.8
U    usr.sbin/jail/jail.8
U    lib/libproc/proc_create.c
U    sys/arm/arm/irq_dispatch.S
U    sys/arm/sa11x0/sa11x0_irq.S
U    sys/powerpc/booke/locore.S
U    sys/powerpc/booke/platform_bare.c
U    sys/powerpc/booke/pmap.c
U    sys/nfsclient/nfsnode.h
U    sys/nfsclient/nfs_node.c
U    sys/kern/kern_jail.c
U    sys/kern/vfs_mount.c
U    sys/fs/nfsclient/nfsnode.h
U    sys/fs/nfsclient/nfs_clnode.c
U    sys/mips/mips/exception.S
U    sys/dev/ahci/ahci.c
U    sys/dev/ata/chipsets/ata-nvidia.c
U    sys/dev/ath/ath_hal/ah_eeprom_v4k.c
U    sys/i386/ibcs2/imgact_coff.c
U    sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c
Updated to revision 224632.

Updating to r224648 (this morning) has had no apparent effect on the
cited panic: it occurs in the same way, at the same time, accompanied by
the same messages (citing the same files and lines).

I've attached dmesg.boot from r224602.

I will see if I can find a commit that affected at least one of the
affected files in the above list that I can revert to avoid the panic,
but I'm a bit slow for a while yet, so I figured I'd finally get around
to posting this, in the hope that someone cleverer than me will spot
the problem and suggest a circumvention to try.

And I'm quite willing to try such things.

Note: this is FreeBSD/i386; nothing special: no jails; running on real
hardware; no attempts to use ZFS....

Peace,
david
-- 
David H. Wolfskill				david_at_catwhisker.org
Depriving a girl or boy of an opportunity for education is evil.

See http://www.catwhisker.org/~david/publickey.gpg for my public key.