One question, how about simultaneous upcalls AUTH_GSS and AUTH_UNIX?
I'm not sure there is the such case, but an error could be taken for the successful case, no? 

This is the auth_gss module, and we always come here to
obtain a GSS security context.  In sec=sys case we might
come here with RPC_AUTH_GSS_KRB5I (see nfs4_alloc_client()
in nfs4client.c), though.  In such case gssd might return an
EACCESS error.

-- 
Minoura Makoto [off-list ref]