panic: LK_RETRY set with incompatible flags

Hi.

Got this assertion on idle NFS server while `ls -la /.zfs/shares/'
issued on NFS client.
kern/vfs_vnops.c:_vn_lock()
                KASSERT((flags & LK_RETRY) == 0 || error == 0,
                    ("LK_RETRY set with incompatible flags (0x%x) or
an error occured (%d)",

panic: LK_RETRY set with incompatible flags (0x200400) or an error occured (11)

What does that mean and how is it possible? As you can see, both parts
of assertion failed.
11 is EDEADLK
0x200400: LK_RETRY & LK_UPGRADE

Tracing pid 2943 tid 101532 td 0xfffffe004f5b7000
kdb_enter() at kdb_enter+0x3e/frame 0xffffff848e45ef50
vpanic() at vpanic+0x147/frame 0xffffff848e45ef90
kassert_panic() at kassert_panic+0x136/frame 0xffffff848e45f000
_vn_lock() at _vn_lock+0x70/frame 0xffffff848e45f070
zfs_lookup() at zfs_lookup+0x392/frame 0xffffff848e45f100
zfs_freebsd_lookup() at zfs_freebsd_lookup+0x6d/frame 0xffffff848e45f240
VOP_CACHEDLOOKUP_APV() at VOP_CACHEDLOOKUP_APV+0xc2/frame 0xffffff848e45f260
vfs_cache_lookup() at vfs_cache_lookup+0xcf/frame 0xffffff848e45f2b0
VOP_LOOKUP_APV() at VOP_LOOKUP_APV+0xc2/frame 0xffffff848e45f2d0
lookup() at lookup+0x548/frame 0xffffff848e45f350
nfsvno_namei() at nfsvno_namei+0x1a5/frame 0xffffff848e45f400
nfsrvd_lookup() at nfsrvd_lookup+0x13a/frame 0xffffff848e45f6b0
nfsrvd_dorpc() at nfsrvd_dorpc+0xca5/frame 0xffffff848e45f8a0
nfssvc_program() at nfssvc_program+0x482/frame 0xffffff848e45fa00
svc_run_internal() at svc_run_internal+0x1e9/frame 0xffffff848e45fba0
svc_thread_start() at svc_thread_start+0xb/frame 0xffffff848e45fbb0
fork_exit() at fork_exit+0x84/frame 0xffffff848e45fbf0
fork_trampoline() at fork_trampoline+0xe/frame 0xffffff848e45fbf0
--- trap 0xc, rip = 0x800883e9a, rsp = 0x7fffffffd488, rbp = 0x7fffffffd730 ---

db> show lockedvnods
Locked vnodes

0xfffffe02e21b11d8: tag zfs, type VDIR
    usecount 4, writecount 0, refcount 4 mountedhere 0
    flags (VI_ACTIVE)
    v_object 0xfffffe02d9f2eb40 ref 0 pages 0
    lock type zfs: EXCL by thread 0xfffffe004f5b7000 (pid 2943, nfsd,
tid 101532)



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