From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1O1Puw-0003d7-0J
	for qemu-devel@nongnu.org; Mon, 12 Apr 2010 16:07:34 -0400
Received: from [140.186.70.92] (port=35615 helo=eggs.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1O1Put-0003cF-Vd
	for qemu-devel@nongnu.org; Mon, 12 Apr 2010 16:07:33 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69)
	(envelope-from <paul@codesourcery.com>) id 1O1Pur-0007Pl-Ib
	for qemu-devel@nongnu.org; Mon, 12 Apr 2010 16:07:30 -0400
Received: from mx20.gnu.org ([199.232.41.8]:61895)
	by eggs.gnu.org with esmtp (Exim 4.69)
	(envelope-from <paul@codesourcery.com>) id 1O1Pur-0007Ph-Gn
	for qemu-devel@nongnu.org; Mon, 12 Apr 2010 16:07:29 -0400
Received: from mail.codesourcery.com ([38.113.113.100])
	by mx20.gnu.org with esmtp (Exim 4.60)
	(envelope-from <paul@codesourcery.com>) id 1O1Pur-0001g8-1G
	for qemu-devel@nongnu.org; Mon, 12 Apr 2010 16:07:29 -0400
From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] How to lock-up your tap-based VM network
Date: Mon, 12 Apr 2010 21:07:18 +0100
References: <4BC34D95.7050804@siemens.com>
In-Reply-To: <4BC34D95.7050804@siemens.com>
MIME-Version: 1.0
Content-Type: Text/Plain;
  charset="iso-8859-15"
Content-Transfer-Encoding: 7bit
Message-Id: <201004122107.19425.paul@codesourcery.com>
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/pipermail/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: qemu-devel@nongnu.org
Cc: Jan Kiszka <jan.kiszka@siemens.com>

> A major reason for this deadlock could likely be removed by shutting
> down the tap (if peered) or dropping packets in user space (in case of
> vlan) when a NIC is stopped or otherwise shut down. Currently most (if
> not all) NIC models seem to signal both "queue full" and "RX disabled"
> via !can_receive().

No. A disabled device should return true from can_recieve, then discard the 
packets in its receive callback. Failure to do so is a bug in the device. It 
looks like the virtio-net device may be buggy.

Paul.