It was reported that there are some exit points in ext4_fill_super which result in destruction of workqueue which is not yet initialized, leading to kernel NULL pointer dereference.
Oops report can be found in product bug:
Upstream fix (only part of the commit is related):
This problem did not affect the Linux kernel packages as shipped with Red Hat Enterprise Linux 5, 7 and MRG-2.
Red Hat would like to thank Dmitriy Monakhov of OpenVZ project for reporting this issue.
This issue has been addressed in the following products:
Red Hat Enterprise Linux 6
Via RHSA-2016:0855 https://rhn.redhat.com/errata/RHSA-2016-0855.html