[kernel-xen] Kernel Panic

Steven Haigh netwiz at crc.id.au
Wed Apr 6 17:54:59 AEST 2016

On 2016-04-06 16:11, Steffan Cline wrote:
> Steven,
> On 4/5/16, 3:22 PM, "kernel-xen on behalf of Steven Haigh"
> <kernel-xen-bounces at lists.wireless.org.au on behalf of
> netwiz at crc.id.au> wrote:
>> On 6/04/2016 1:11 AM, Steffan Cline wrote:
>>> Had an odd issue a couple weeks back where I checked on my server and
>>> there was a kernel panic. I didn’t think much of it and restarted. It
>>> booted into the default CentOS 6 kernel. Once I realized what 
>>> happened I
>>> rebooted back into the Xen kernel just fine.
>>> This morning I woke to find that the server had been crashing and
>>> rebooting for several hours.
>>> I logged in and the cause seems to be the notorious error "module
>>> scsi_wait_scan not found” There are no good easy solutions on how to 
>>> fix
>>> this.
>> This isn't a crash. The error shows because the module doesn't exist.
>> I'm not keep on patching the init scripts of EL6 to remove the message
>> as that has the potential to cause more problems than to remove a
>> cosmetic only error.
> Can you please tell me how to patch it? I’ll happily boot back to an
> older kernel, change it and reboot.

You can edit /etc/rc.sysinit - note that this is NOT a file shipped with 
any kernel and is critical to your system functioning.

It does:
{ rmmod scsi_wait_scan ; modprobe scsi_wait_scan ; rmmod scsi_wait_scan 
; } >/dev/null 2>&1

As you can see, it does nothing.

>>> Most docs I came across say it was supposed to be removed a while 
>>> back.
>> And it has - hence you see the 'error'.
> That ‘error’ repeated itself about a dozen times before the computer
> crashed and rebooted repeatedly. I should have taken a screenshot to
> be able to document some of the different kernel panics I saw when
> trying different kernels. One I did see was usb 1-3.3: device
> descriptor read/8, error -110 on a couple different kernels. The RAM
> did pass the memory checks if that matters.

It may show multiple times - however its function is nothing. It will 
not be the source of your problem.

>>> Suggestions anyone? I only got my system back up by using an older 
>>> Xen
>>> kernel. Hard part is my mail runs in a VM on the system. Such luck.
>> Which kernel were you using? DomU configuration? Dom0 configuration? 
>> Are
>> you using PVH? Linux guest? Windows guest? 'Older Xen kernel' in what?
>> The DomU? The Dom0?
> I was using kernel-xen-4.4.6-2.el6xen.x86_64. I’m only a novice with
> virtualization but if I have it right, it’s Dom0.
> The host is CentOS 6.7 and I had 2 CentOS 6.7 guests and a Windows
> Server 2008R2 goes.
> The older kernel I reverted to in order to get the system back up is
> 4.4.4-2.el6xen.x86_64.

I'd start by looking in /boot to see what is going on. Maybe your 
initramfs didn't get created when 4.4.6-2 was installed. Maybe there's a 
compatibility issue / bug on this kernel version on your hardware.

>> As a side note, I'd recommend removing the stock kernels on the Dom0 -
>> it will operate quite fine without them.
> I’d heard that before too but if it wasn’t for that, I’d wouldn’t have
> been able to get it back up and check everything first. I’ll probably
> do that once I figure out how to fix this.

Do you mean that you booted into a stock kernel, then the the kernel-xen 
4.4.4-2? If so, this should still boot without the stock EL kernels 

Steven Haigh

Email: netwiz at crc.id.au
Web: https://www.crc.id.au
Phone: (03) 9001 6090 - 0412 935 897

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