UVM_VNODE_DYING
if (uvn->u_flags & UVM_VNODE_DYING) {
uvn->u_flags |= UVM_VNODE_DYING;
uvn->u_flags |= UVM_VNODE_DYING|UVM_VNODE_VNISLOCKED;
uvn->u_flags &= ~(UVM_VNODE_DYING|UVM_VNODE_VNISLOCKED|
dying = (uvn->u_flags & UVM_VNODE_DYING);
#define UVM_VNODE_BLOCKED (UVM_VNODE_DYING|UVM_VNODE_RELKILL)