Description of problem:
I run my rawhide system from a RAID-1 md device. Since I think the standard GRUB2 menus look nicer than the "grubby" ones, I always run grub2-mkconfig after a kernel update when my "yum update" finishes. That script calls the os-prober, the os-prober script hangs at the 'newns "$@"' command, which never returns. (/usr/libexec/newns is part of the os-prober rpm package.)

Version-Release number of selected component (if applicable):
The os-prober rpm is version 1.58=1.0.fc22.x86_64
 
How reproducible:
Every time

Steps to Reproduce:
1. Open a su terminal
2. Enter the os-prober command
3. See a few lines, and then wait "forever" (well, I waited am hour, but
   all the os-prober processes were in the "S+" state.)

Actual results:
Hung process

Expected results:
List of all installed systems

Additional info: 

Here's some terminal output:

Running os-prober:
[root ~]# os-prober 
/dev/sda1:Windows 7 (loader):Windows:chain
/dev/sda3:Windows Recovery Environment (loader):Windows1:chain
/dev/sdb1:Fedora release 20 (Heisenbug):Fedora:linux
=========================
(Note that the RAID 1 array components are reported in the "raided" file in /tmp, as shown below, in addtion to the actual mount (/dev/md127) shown in the mounted-map file.)

Speculation: Could the newns program be trying to re-mount a mounted RAID component instead of using the already mounted array? In fact, why would 'os-prober' need to know anything about a raid device except its logical name? Unless it's looking for bootable os's on unmounted RAID devices, and it's hung trying to mount the RAID array containing the woking system in, e.g., /var/lib/os-prober/mount to look for the rawhide os. (My system is all in a single ext4 file system.)

From another terminal:
[root ~]# ps -aux | egrep '(19648)|(19725)|(19726)'
root     19648  0.0  0.0 113824  3256 pts/3    S+   20:52   0:00 /bin/sh /bin/os-prober
root     19725  0.0  0.0 113824  1540 pts/3    S+   20:52   0:00 /bin/sh /bin/os-prober
root     19726  0.0  0.0 113824  2312 pts/3    S+   20:52   0:00 /bin/sh /bin/os-prober

Here's the /tmp files that were generated before the hang. (They all seem correct):
[root ~]# ls /tmp/os-prober.MxQGsY/
btrfs-vols  mounted-map  raided-map  swaps-map
==========================
[root ~]# cd /tmp/os-prober.MxQGsY/
==========================
[root os-prober.MxQGsY]# cat btrfs-vols 
da1e3dad-5460-4a45-95b6-a1c3d43f760d
=========================
[root os-prober.MxQGsY]# cat mounted-map 
/dev/md127 / ext4 /dev/md127
/dev/sdb1 /Fedora ext4 /dev/sdb1
/dev/sdc1 /Backups btrfs /dev/sdc1
/dev/sda2 /Win7 fuseblk /dev/sda2
/dev/sda1 /Win7/System fuseblk /dev/sda1
/dev/sda3 /Win7/HP_Recover fuseblk /dev/sda3
========================
[root os-prober.MxQGsY]# cat raided-map 
/dev/sda5
/dev/sdb2
========================
[root os-prober.MxQGsY]# cat swaps-map 
/dev/sdc2 swap
=======================
root ~]# kill -hup 19648 19725 19726

(The os-prober scrpt traps the hangup and removes the /tmp files.)