zfs kernel messages

while playing a little with zfs i get the following
kernel messages at ttyv0 (no panic/freeze happend)

(captured vi ssh from other system)
# vidcontrol -P < /dev/ttyv0

uma_zalloc_arg: zone "256" with the following non-sleepable locks held:
exclusive sleep mutex struct mount mtx r = 0 (0xc64e7d3c) locked _at_ /usr/src/sys/modules/zfs/../../compat/opensolaris/kern/opensolaris_vfs.c:206
KDB: stack backtrace:
db_trace_self_wrapper(c0a9c175,e72bb6e4,c078428d,c0a9c538,e72bb6f8,...) at db_trace_self_wrapper+0x26
kdb_backtrace(c0a9c538,e72bb6f8,4,1,0,...) at kdb_backtrace+0x29
witness_warn(5,0,c0aba40d,c0ac3e77,1,...) at witness_warn+0x1cd
uma_zalloc_arg(c146d1e0,0,102,2,c64e7d0c,...) at uma_zalloc_arg+0x34
malloc(94,c0b4c4e0,102,c64e7d0c,e72bb790,...) at malloc+0xd2
crget(c6985300,c0b4c4e0,c64e7d0c,e72bb7d4,c431b9dc,...) at crget+0x23
crdup(c3f07600,0,c439444c,ce,c2,...) at crdup+0xc
domount(c450a420,c6ee4330,c43995db,cc152900,e72bb810,...) at domount+0x20c
zfsctl_snapdir_lookup(e72bbaa0,e72bbaa0,c450a420,2,c456e660,...) at zfsctl_snapdir_lookup+0x362
VOP_LOOKUP_APV(c439d5c0,e72bbaa0,c450a420,c0aa409d,19b,...) at VOP_LOOKUP_APV+0xa5
lookup(e72bbb48,c0aa409d,c6,bf,c730102c,...) at lookup+0x58e
namei(e72bbb48,e72bbb94,60,0,c450a420,...) at namei+0x34b
kern_lstat(c450a420,28220318,0,e72bbc18,2d4738cb,...) at kern_lstat+0x4f
lstat(c450a420,e72bbcfc,8,c0a9ed42,c0b469d0,...) at lstat+0x2f
syscall(e72bbd38) at syscall+0x2b3
Xint0x80_syscall() at Xint0x80_syscall+0x20
--- syscall (190, FreeBSD ELF32, lstat), eip = 0x2815548b, esp = 0xbfbfe93c, ebp = 0xbfbfe9c8 ---



System: 7.0-CURRENT-200710, GENERIC i386, 1GB RAM
entries in loader.conf
   vfs.zfs.prefetch_disable="1"    # (loader.conf)
   vfs.zfs.arc_max="104857600"     # (loader.conf)
   vm.kmem_size_max="402653184"    # (loader.conf)

entries in sysctl.conf
    kern.maxvnodes="50000"        # (sysctl)

It is not easy to reproduce but i get the message this way:
- enable shell command line completion
- zfs snapshot zvol/test_at_snapX
- ls -l /zvol/test/.zfs/snap  -> tab

Once i get the message i have to create a new snapshot to reproduce this

olli