Created attachment 443269 [details]
libguestfs-test-tool boot OK (line removed)

Description of problem:

The following line in the libguestfs /init file:

for f in /sys/block/[hsv]d*/queue/scheduler; do echo noop > $f; done

If it is there, then the boot hangs at this line.  If this line is removed
then the boot continues fine.

I don't know if this is a problem in kernel or qemu-kvm (or very unlikely
in udev).  It seems like it would be a virtio-blk driver bug in the kernel
which is why I'm initially assigning this bug to kernel.

There is no kernel error message, and the kernel does not panic, it (or
something) just hangs.

Version-Release number of selected component (if applicable):

# yum --enablerepo=koji install udev kernel qemu-kvm
Package udev-161-2.fc15.i686 already installed and latest version
Package kernel-2.6.36-0.16.rc3.git0.fc15.i686 already installed and latest version
Package 2:qemu-kvm-0.13.0-0.5.20100809git25fdf4a.fc15.i686 already installed and latest version

How reproducible:

Always.
This hang has been happening for over a month in the same place.

Steps to Reproduce:

Install the above packages, and run libguestfs-test-tool.
  
Actual results:

Hangs at this line.

Expected results:

Should not hang, or should give an error message.

Additional info:

The full output of libguestfs-test-tool (with the problem line REMOVED
so it boots OK) is in the attachment.  This contains useful information
such as the full kernel and qemu-kvm command lines.