Hi Steffen,

0day kernel testing robot got the below dmesg and the first bad commit is

git://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git master
commit 78ff4be45a4c51d8fb21ad92e4fabb467c6c3eeb
Author:     Steffen Klassert <steffen.klassert@secunet.com>
AuthorDate: Mon May 19 11:36:56 2014 +0200
Commit:     David S. Miller <davem@davemloft.net>
CommitDate: Wed May 21 02:08:32 2014 -0400

     ip_tunnel: Initialize the fallback device properly
         We need to initialize the fallback device to have a correct mtu
     set on this device. Otherwise the mtu is set to null and the device
     is unusable.
         Fixes: fd58156e456d ("IPIP: Use ip-tunneling code.")
     Cc: Pravin B Shelar <pshelar@nicira.com>
     Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
     Signed-off-by: David S. Miller <davem@davemloft.net>

+--------------------------------------------------------------------------------+------------+------------+
|                                                                                | d8d33c3b8a | 78ff4be45a |
+--------------------------------------------------------------------------------+------------+------------+
| boot_successes                                                                 | 60         | 0          |
| boot_failures                                                                  | 0          | 20         |
| WARNING:CPU:PID:at_net/batman-adv/hard-interface.c:batadv_is_on_batman_iface() | 0          | 20         |
| backtrace:register_netdevice_notifier                                          | 0          | 20         |
| backtrace:batadv_init                                                          | 0          | 20         |
| backtrace:kernel_init_freeable                                                 | 0          | 20         |
+--------------------------------------------------------------------------------+------------+------------+


[   31.090120] libceph: loaded (mon/osd proto 15/24)
[   31.090854] ------------[ cut here ]------------
[   31.090854] ------------[ cut here ]------------
[   31.091497] WARNING: CPU: 1 PID: 1 at net/batman-adv/hard-interface.c:92 batadv_is_on_batman_iface+0x62/0x70()

git bisect start 842390939e8dc18fe8a87e257e7e8088548bd8d7 d6d211db37e75de2ddc3a4f979038c40df7cc79c --
git bisect  bad 6e8a2e89a46e99e7750d8511b94c6e964fa62041  # 18:29      0-     20  Merge 'arm-soc/keystone/dt' into devel-hourly-2014052115
git bisect  bad 732aed36300f1426c6da40602fbaf23dd79d8391  # 19:21      0-      1  Merge 'tip/irq/core' into devel-hourly-2014052115
git bisect good fd69bb2faebc552b4da42966ee51e1dea9ba77e6  # 19:28     20+      0  Merge 'block/for-3.16/drivers' into devel-hourly-2014052115
git bisect  bad 917a4d3aed6301097ff8a2b2bb74be34be5c9b23  # 19:39      0-      5  Merge 'net/master' into devel-hourly-2014052115
git bisect good 6c8b235f29b6b756379d7d5d86371a9f399afa52  # 20:04     20+      0  Merge 'hwmon/hwmon-next' into devel-hourly-2014052115
git bisect good 70c0859af3e380a0508883120adac883b456b056  # 21:09     20+      0  Merge 'kees/lsm-mnt-restrict' into devel-hourly-2014052115
git bisect good b394745df2d9d4c30bf1bcc55773bec6f3bc7c67  # 21:31     20+      0  net: phy: Don't call phy_resume if phy_init_hw failed
git bisect good 202630b445d2618d94e4f099567fcee5618dab27  # 22:25     20+      0  Merge branch 'for-davem' of git://git.kernel.org/pub/scm/linux/kernel/git/linville/wireless
git bisect good 0d08fceb2e21c30ca3e1e462e678723f806acf18  # 23:18     20+      0  xen-netback: fix race between napi_complete() and interrupt handler
git bisect good 25175ba5c9bff9aaf0229df34bb5d54c81633ec3  # 00:28     20+      0  net: Allow for more then a single subclass for netif_addr_lock
git bisect good 5467a512216753d54f757314c73dbc60f659f9e6  # 03:39     20+      0  netfilter: nf_tables: fix goto action
git bisect good c674ac30c549596295eb0a5af7f4714c0b905b6f  # 04:12     20+      0  macvlan: Fix lockdep warnings with stacked macvlan devices
git bisect good e1618d461ca18d40f9c3ef70598abb72e75d27ae  # 07:14     20+      0  vlan: Fix build error wth vlan_get_encap_level()
git bisect good 3b084e99a3fabaeb0f9c65a0806cde30f0b2835e  # 07:47     20+      0  netfilter: nf_tables: fix trace of matching non-terminal rule
git bisect good d8d33c3b8a42fbd9ad23a61498fa5db1d83644e0  # 08:09     20+      0  Merge tag 'linux-can-fixes-for-3.15-20140519' of git://gitorious.org/linux-can/linux-can
git bisect  bad 78ff4be45a4c51d8fb21ad92e4fabb467c6c3eeb  # 08:52      0-     13  ip_tunnel: Initialize the fallback device properly
# first bad commit: [78ff4be45a4c51d8fb21ad92e4fabb467c6c3eeb] ip_tunnel: Initialize the fallback device properly
git bisect good d8d33c3b8a42fbd9ad23a61498fa5db1d83644e0  # 08:55     60+      0  Merge tag 'linux-can-fixes-for-3.15-20140519' of git://gitorious.org/linux-can/linux-can
git bisect  bad 842390939e8dc18fe8a87e257e7e8088548bd8d7  # 08:55      0-     13  0day head guard for 'devel-hourly-2014052115'
git bisect good 4b660a7f5c8099d88d1a43d8ae138965112592c7  # 09:59     60+      0  Linux 3.15-rc6
git bisect good 18e072998c67e985aaa643ca1af3e6a0dc133b71  # 11:54     60+     60  Add linux-next specific files for 20140521


This script may reproduce the error.

-----------------------------------------------------------------------------
#!/bin/bash

kernel=$1

kvm=(
	qemu-system-x86_64 -cpu kvm64 -enable-kvm 	-kernel $kernel
	-smp 2
	-m 256M
	-net nic,vlan=0,macaddr=00:00:00:00:00:00,model=virtio
	-net user,vlan=0
	-net nic,vlan=1,model=e1000
	-net user,vlan=1
	-boot order=nc
	-no-reboot
	-watchdog i6300esb
	-serial stdio
	-display none
	-monitor null
)

append=(
	debug
	sched_debug
	apic=debug
	ignore_loglevel
	sysrq_always_enabled
	panic=10
	prompt_ramdisk=0
	earlyprintk=ttyS0,115200
	console=ttyS0,115200
	console=tty0
	vga=normal
	root=/dev/ram0
	rw
)

"${kvm[@]}" --append "${append[*]}"
-----------------------------------------------------------------------------

Thanks,
Jet