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-- Problem Description --
Trying to dynamically add a network device of type virtio to a Ubuntu 14.10 guest running on PowerKVM generates a kernel BUG message. Virsh reports the operation as successful.

Steps to recreate the problem :

1) Install 14.10 as a Power KVM guest.
2) Install ppc64-diag package

librtas1                  1.3.10-1                     ppc64el      userspace RTAS library
librtasevent1        1.3.10-1                     ppc64el      RTAS events library
ppc64-diag           2.6.6-0ubuntu1               ppc64el      Platform error log analysis tool and rtas_errd daemon
libservicelog-1.1-1:ppc64el        1.1.14-0ubuntu1              ppc64el      Library to create and maintain a database for storing events
servicelog             1.1.12-0ubuntu1              ppc64el      Platform Service/Error Message Database

3) Using a network device definition as mentioned below try a virsh
attach-device operation

On the PowerKVM host :

# cat net
<interface type='bridge'>
   <mac address='52:54:00:A0:9D:9a'/>
   <source bridge='virbr0'/>
   <model type='virtio'/>
</interface>

# virsh attach-device ss_1410_1 net
Device attached successfully

#

Following kernel BUG is observed on the guest

[ 6380.112079] RTAS: event: 1, Type: Unknown, Severity: 1
[ 6380.209844] ------------[ cut here ]------------
[ 6380.209848] kernel BUG at /build/buildd/linux-3.15.0/drivers/of/base.c:251!
[ 6380.209922] Oops: Exception in kernel mode, sig: 5 [#1]
[ 6380.209963] SMP NR_CPUS=2048 NUMA pSeries
[ 6380.210006] Modules linked in: pseries_rng rtc_generic e1000
[ 6380.210084] CPU: 0 PID: 3642 Comm: drmgr Not tainted 3.15.0-6-generic #11-Ubuntu
[ 6380.210146] task: c0000000770968a0 ti: c000000079858000 task.ti: c000000079858000
[ 6380.210207] NIP: c000000000871c24 LR: c000000000872704 CTR: c000000000080ed0
[ 6380.210268] REGS: c00000007985b7f0 TRAP: 0700   Not tainted  (3.15.0-6-generic)
[ 6380.210328] MSR: 8000000000029033 <SF,EE,ME,IR,DR,RI,LE>  CR: 24002488  XER: 20000000
[ 6380.210473] CFAR: c000000000872700 SOFTE: 1 
[ 6380.210473] GPR00: c000000000872704 c00000007985ba70 c000000001791188 c000000004192100 
[ 6380.210473] GPR04: 0000000000000001 c00000007e039fc0 c00000000419ee80 c000000001aa1188 
[ 6380.210473] GPR08: 0000000000000002 0000000000000001 0000000000000000 c00000000453025b 
[ 6380.210473] GPR12: 0000000024002482 c00000000fe40000 0000000000000000 000000000000000c 
[ 6380.210473] GPR16: 000001001e42eeda 0000000000000020 0000000000000000 0000000010016a00 
[ 6380.210473] GPR20: 0000000010016950 00000000100167b0 0000000000000001 c00000007e039800 
[ 6380.210473] GPR24: c000000000cc0310 c000000004530009 c000000077594f80 c00000007fff6d38 
[ 6380.210473] GPR28: 0000000000000015 c000000004192100 c000000001aa01b0 c000000004192100 
[ 6380.211355] NIP [c000000000871c24] .of_node_add+0x34/0x110
[ 6380.211397] LR [c000000000872704] .of_attach_node+0xd4/0xf0
[ 6380.211440] Call Trace:
[ 6380.211462] [c00000007985ba70] [0000000010016950] 0x10016950 (unreliable)
[ 6380.211525] [c00000007985baf0] [c000000000872704] .of_attach_node+0xd4/0xf0
[ 6380.211633] [c00000007985bb70] [c000000000076420] .ofdt_write+0x590/0x780
[ 6380.211753] [c00000007985bc50] [c00000000030727c] .proc_reg_write+0xac/0x110
[ 6380.211815] [c00000007985bcf0] [c000000000279370] .vfs_write+0xe0/0x260
[ 6380.211876] [c00000007985bd90] [c00000000027a034] .SyS_write+0x64/0x110
[ 6380.211939] [c00000007985be30] [c000000000009ffc] syscall_exit+0x0/0x7c
[ 6380.212001] Instruction dump:
[ 6380.212033] fbc1fff0 fbe1fff8 f8010010 f821ff81 7c7f1b78 60000000 60000000 2fbf0000 
[ 6380.212142] 419e006c 813f0094 69290001 792907e0 <0b090000> 3fc2ffeb 3bdefe60 7fc3f378 
[ 6380.212250] ---[ end trace 410b60b95ac50ef5 ]---
[ 6380.214151] 
sachin@1410:/var/log$ 

sachin@1410:/var/log$ cat /etc/issue
Ubuntu Utopic Unicorn (development branch) \n \l

sachin@1410:/var/log$ uname -a
Linux 1410 3.15.0-6-generic #11-Ubuntu SMP Thu Jun 12 00:40:49 UTC 2014 ppc64le ppc64le ppc64le GNU/Linux
sachin@1410:/var/log$

The BUG_ON() it is hitting is likely this one:

int of_node_add(struct device_node *np)
{
	int rc = 0;

        BUG_ON(!of_node_is_initialized(np));

This appears to be related to commit
75b57ecf9d1d1e17d099ab13b8f48e6e038676be.

This was part of the updates that Grant did to move the device tree from
/proc/to sysfs. As part of this he removed the kref_init call we made
prior to adding the device node.

Attached patch "powerpc/pseries: dynamically added OF nodes need to call
of_node_init"

With the attach patch, the attach/detach device operation works
correctly. No kernel BUG is observed.

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: architecture-ppc64le bugnameltc-112395 severity-critical
-- 
Kernel BUG @of/base.c:251 during attach-device operation on Ubuntu 14.10 LE guest
https://bugs.launchpad.net/bugs/1340789
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