Hi,

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.

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.  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.

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.

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.

All the instances I've seen this on are upgraded from at least 12.04.
Some from 10.04.  So there are ext3 -> ext4 -> ext4+ options involved in
the filesystem makeup.  Reading some of the bugs on the kernel list, it
feel like this might be related to that an it will be complicated.

I've attached to examples from tune2fs to show that I have different
features attached to the different servers that are experiencing this
issue.

If you can provide any debugging advise that would be good, I've not
really done kernel debugging before.  I done a lot in the application
space so I understand all the concepts.

** Attachment added: "tune2fs output from bob server."
   
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1298972/+attachment/4222242/+files/bob.txt

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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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