igb_attach has this code 

err_late:
        igb_detach(dev);
        igb_free_transmit_structures(adapter);
        igb_free_receive_structures(adapter);
        igb_release_hw_control(adapter);
err_pci:
        igb_free_pci_resources(adapter);
        if (adapter->ifp != NULL)
                if_free(adapter->ifp);
        free(adapter->mta, M_DEVBUF);
        IGB_CORE_LOCK_DESTROY(adapter);

        return (error);

However, I see that igb_detach does all this cleanup when it's successfully completed. Only exception I see is that it return EBUSY if vlantrunk is in use
        /* Make sure VLANS are not using driver */
        if (if_vlantrunkinuse(ifp)) {
                device_printf(dev,"Vlan in use, detach first\n");
                return (EBUSY);
        }

This results in duplicate cleanup in igb_attach and can cause crashes. 
The fix would be the following. 
Index: if_igb.c
===================================================================
--- if_igb.c	(revision 298053)
+++ if_igb.c	(working copy)
@@ -723,7 +723,8 @@ igb_attach(device_t dev)
 	return (0);
 
 err_late:
-	igb_detach(dev);
+	if(igb_detach(dev) == 0) /* igb_detach did the cleanup */
+		return(error); 
 	igb_free_transmit_structures(adapter);
 	igb_free_receive_structures(adapter);
 	igb_release_hw_control(adapter);


The issue exists in stable/10 as well as current.