On Sun, Sep 16, 2012 at 10:07:39PM -0600, Kay Sievers wrote:

I'm currently playing around with native btrfs multi-device support in
systemd. There might be a few "hotplug issues" to solve, here is the
first one:

A mounted (otherwise unused) multi-device volume (USB multi-slot card
reader), hangs at:
  $ umount /mnt
with (fedora) kernel
  3.6.0-0.rc5.git0.1.fc18.x86_64

Any idea what to look for or what to try?

Can I see the whole sysrq+w?  Also can you try btrfs-next and see if you have
the same problems?  Thanks,

Josef