Hi Russell,

On 10/02/2014 06:06 AM, Russell Smith wrote:
> I behaved lazily...  and have been trying to collect more data before
> posting back.  Sorry for the delay.
> 
> 1. I can only reproduce the bug about once a week on 3.13 kernel that is 
> running on ubuntu 14.04.
> 2. I was lazy and after reading patches and kernel stuff, I marked it as 
> fixed upstream.  I didn't want to go compiling my own kernel as I need all 
> the virtio options.

Ubuntu provides upstream kernels here:

 http://kernel.ubuntu.com/~kernel-ppa/mainline/?C=N;O=D

And some documentation about it is available here:

 https://wiki.ubuntu.com/Kernel/MainlineBuilds

> I have 5 virtual machines running on top of a md10 + md1 raid all put
> into a single lvm volume.  The host is running ubuntu 12.04 with a 3.2
> kernel series.  The guests are all virtio and running 14.04 as they have
> been upgraded.

Interestingly I also had an hypervisor running 12.04 and possibly with
the 3.2 or the 3.11 kernel. IIRC, the guest was running a fresh install
of 14.04.

Since then, I reinstalled the hypervisor with 14.04 and the guest too. I
never experienced this problem after this.

>  Most of the 5 instances have experienced a file system
> read-only event.  One server has experienced 3.  It is my package mirror
> running approx.

IIRC, my guest was an apt-cacher-ng instance.

> So after further investigation this may not be resolved upstream.  If
> you can provide me with a virtio/ubuntu compatible newer kernel I can
> put it on a machine and try it out.  But because I can't reproduce this
> at will it's very hard to give a reproduction case.

Indeed but since I haven't reproduce this issue once I'm afraid I can't
help you here.

> I found http://lists.openwall.net/linux-ext4/2014/05/21/2 which
> indicates there is a bug somewhere if we are seeing failures where we
> are.  The result of that thread was more debugging put into the section
> of code that reports this.  I'm happy to track and patch any amount of
> debug.
> 
> As the filesystem re-mounts readonly, I suspect I should move /var/log
> onto another filesystem to increase the chances I'll log everything.

You can also send the logs to a remote syslog server.

Good luck and thanks!
Simon

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https://bugs.launchpad.net/bugs/1298972

Title:
  stacktrace in ext4: /build/buildd/linux-3.13.0/fs/ext4/ext4_jbd2.c:259
  __ext4_handle_dirty_metadata+0x1a2/0x1c0()

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