i386 panic in nfs_vnops: assertion "dvp != *vpp" failed

[Hubert Feyrer <hubert%feyrer.de@localhost>]

I'm seeing repeated panics on i386/current with src on nfs when building a 
release. according to savecore, the panic message is:

        panic: kernel diagnostic assertion "dvp != *vpp" failed: file 
".../src-current/sys/nfs/nfs_vnops.c", line 817

the source code at line 817 is:

        error = cache_lookup_raw(dvp, vpp, cnp);
-->     KASSERT(dvp != *vpp);
        KASSERT((cnp->cn_flags & ISWHITEOUT) == 0);


 - Hubert