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Date:	Wed, 4 Jul 2012 19:04:43 +0800
From:	RuanZhijie <ruanzhijie@...mail.com>
To:	<davem@...emloft.net>
CC:	<netdev@...r.kernel.org>, <skinsbursky@...allels.com>
Subject: Kernel Oops


Hi, all.

Mr. Stanislav Kinsbursky suggests me send you a report about an oops I encountered in the past few days.

A few days ago, I tested some VMs with NAT enabled under KVM and libvirt, but kernel crashed when I shut down these VMs, though this issue did not occur every time. I did some search and found a webpage (http://www.spinics.net/lists/netdev/msg193846.html) in which Simon reported a similar issue.

The operating system I use is gentoo-amd64 with no-multilib profile, kernel version is 3.4.0, libvirt-0.9.13 with USE flag "qemu virt-network" enabled and qemu-kvm-1.0.1-r1. Here are the steps to reproduce:

1. Let's define that starting a VM with NAT enabled under KVM and libvirt and then shut it down immediately as one operation.
2. Repeat the operation for several times.

I also did 3 tests:

Test 1: 
The host machine is with a regular linux 3.4.0 kernel, and the VM had NAT enabled. Kernel crashed after 2, 7 and 13 operations.

Test 2:
The host machine is with a regular linux 3.4.0 kernel, and the VM had no network access. No crash occured after 100 operations.

Test 3:
The host machine is with a linux 3.4.0 kernel, but drivers/net/tun.c was reverted back to just before commit 1ab5ecb90cb6a3df1476e052f76a6e8f6511cb3d (https://github.com/torvalds/linux/commit/1ab5ecb90cb6a3df1476e052f76a6e8f6511cb3d#drivers/net/tun.c), (or you can use a tun.c from a 3.2.0 kernel, according to Simon's report), and the VM had NAT enabled. No crash occured after 100 operations.

Moreover, I observe that a virtual interface is created to handle network access when a VM with NAT enabled starts, and the virtual interface is removed when the VM is shut down. Crashes usually occur at the time the virtual interface is removed.

Finally, the attachment contains the config file I use to compile the kernel and the kernel crash traces. I am sorry that my laptop does not have a serial port, I could not provide traces from tty console. Hope these could help.

Sincerely,

Zhijie 		 	   		  
Download attachment "kernel.config" of type "application/octet-stream" (61488 bytes)

Download attachment "IMG_20120701_214046.jpg" of type "image/jpeg" (598974 bytes)

Download attachment "IMG_20120704_095542.jpg" of type "image/jpeg" (788176 bytes)

Download attachment "IMG_20120704_162510.jpg" of type "image/jpeg" (798134 bytes)

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