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[Xen-bugs] [Bug 1701] New: A PV VM won't start after being rebooted.

To: xen-bugs@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-bugs] [Bug 1701] New: A PV VM won't start after being rebooted.
From: bugzilla-daemon@xxxxxxxxxxxxxxxxxxx
Date: Mon, 3 Jan 2011 08:30:16 -0800
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           Summary: A PV VM won't start after being rebooted.
           Product: Xen
           Version: unstable
          Platform: x86-64
        OS/Version: Linux-2.6
            Status: NEW
          Severity: major
          Priority: P2
         Component: Tools
        AssignedTo: xen-bugs@xxxxxxxxxxxxxxxxxxx
        ReportedBy: xiaohm@xxxxxxxxx
                CC: xiaohm@xxxxxxxxx

1. Problem

If the configuration of a PV VM contains following line, the VM won't be able
to start after being rebooted if it is under xend domain management.  

vfb = [ "type=vnc, vncunused=0, vncdisplay=10" ]

2. Environment

Xen Version: Xen-3.4.2-2, 64 bit. 
Domain-0 OS: Linux version 2.6.18-194.11.4.el5xen
(mockbuild@xxxxxxxxxxxxxxxxxxxx) (gcc version 4.1.2 20080704 (Red Hat
4.1.2-48)) #1 SMP Tue Sep 21 05:40:24 EDT 2010
PV-VM OS: Linux version 2.6.18-194.11.4.el5xen (mockbuild@xxxxxxxxxxxxxxxxxxxx)
(gcc version 4.1.2 20080704 (Red Hat 4.1.2-48)) #1 SMP Tue Sep 21 05:40:24 EDT

3. Steps to reproduce

VM Configuration: /etc/xen/abc

name = "abc"
uuid = "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"
maxmem = "3072"
memory = "3072"
vcpus = "4"
bootloader = "/usr/bin/pygrub"
> >>vfb = [ "type=vnc, vncunused=0, vncdisplay=10" ]
disk = [ "phy:/dev/VolGroup00/lv_xxx,xvda,w", ]
vif = ["mac=xx:xx:xx:xx:xx:xx,bridge=abcd", "mac=xx:xx:xx:xx:xx:xx,bridge=def"

Once the VM is created, the problem can be consistently reproduced using
following commands,

#xm new abc
#xm start abc
#xm reboot abc

Connecting to VM's console at this moment will see following messages, as

Turning off swap:
Unmounting file systems:
Please stand by while rebooting the system...
Restarting system.

However, the VM won't start up even though it says "Restaring system".
Connecting to the console at this time, the console shows nothing. xm list
displays the state of the vm as following,

mss                                         31  3072     4     -b----      1.5

Instead of using "xm reboot abc", the problem can also be reproduced if ssh to
the VM and issues a reboot command. 

4. Further findings:

a) Replace vfb = [ "type=vnc, vncunused=0, vncdisplay=10" ] with vfg = [ ] in
/etc/xen/abc can solve the problem. However, we have to enable VNC. 

b) Following methods can be used to start the VM after the VM is in problem,

Method 1:
# xm destroy abc
# xm new abc
# xm start abc

Method 2:

# xm destroy abc
# xm creat abc

Method 3:

# xm destroy abc
# service xend stop

Remove following line from 
            (protocol vt100)
            (location 2)
            (uuid e0ad7f84-107b-4ff7-0378-43f40442d8f7)

Be noted that above lines are added by xend when executing "xm destroy abc" or
"service xend stop". When the file is created when running "xm new abc", it
doesn't have above lines. Are these new added lines conflict with VNC
configuration, somehow?

After removing above lines, the VM can be started using following commands,

# service xend start
# xm start abc

5. Any suggestion?

Is there any solution if we have to support all of following features?

a) have to configure VNC for the VM
b) have to add VM under Xend management by using "xm new" 
c) have to allow a VM rebooting itself

More information about this problem:

a) Xen-3.4.2-2 package is downloaded from getco.de
b) Xen 3.3.0, also downloaded from getco.de, doesn't have this issue
c) This problem doesn't affect any HVM.
d) This is a very easy to reproduce problem.

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