Without a complete dmesg it's hard to say what's going on. The call trace alone probably don't show the instigating factor so you may need to use remote ssh with journalctl -f, or use netconsole to continuously get kernel messages prior to the implosion.
Chris Murphy -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
