From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mark van Dijk Subject: Possible bug with huge unflushed console buffer Date: Wed, 8 Aug 2012 17:43:55 +0200 Message-ID: <20120808174355.470746e0@internecto.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: xen-devel@lists.xen.org Cc: Konrad Rzeszutek Wilk List-Id: xen-devel@lists.xenproject.org Greetings list, Yesterday the following scenario took place. In short, I had a HVM host with a poorly configured firewall. It logged way more than it should, and it had been doing that for days. IPTables entries with -j LOG show up in the console. I told Konrad about this but I said it was a PV host while in fact it is concerning a HVM host. Anyway, when I saw that this was the case I corrected iptables and then I removed those faulty log entries from the logfiles in /var/log. Finally I issued /etc/init.d/rsyslogd reload. Suddenly the server stopped responding at all, not even arp requests were answered. I opened up a console via xl (none was open before this) and I was greeted with a crazy amount of log entries - it took about five or six minutes before the whole buffer was flushed to my screen. Then the server responded again. Today I viewed syslog's messages in detail and found this and a lot of similar entries: http://pastebin.com/Ga7aE7hb So the questions that I have now are - Is this a bug? How is console history handled and where is the console's unread history stored? Somewhere in the hypervisor or in dom0 or domU memory space? Is there a limit to how much info can be stored? The behaviour I encountered i.e. a system lock seems to suggest that there was some kind of buffer overflow. And this can be achieved by something as simple as 'iptables -I INPUT -j LOG'. Perhaps it is a wise idea to consider xl console -c to clear the console's history, then at least I could exit the console and clear unsent messages... I am not receiving xen-devel messages, so please CC me on replies. Thank you. -- Stay in touch, Mark van Dijk. ,----------------------------------- -------------------------------' Wed Aug 08 15:29 UTC 2012 Today is Setting Orange, the 1st day of Bureaucracy in the YOLD 3178