The pmd_none_or_trans_huge_or_clear_bad function in include/asm-generic/pgtable.h in the Linux kernel before 3.13 on NUMA systems does not properly determine whether a Page Middle Directory (PMD) entry is a transparent huge-table entry, which allows local users to cause a denial of service (NULL pointer dereference and system crash) or possibly have unspecified other impact via a crafted MADV_WILLNEED madvise system call that leverages the absence of a page-table lock.
https://github.com/torvalds/linux/commit/ee53664bda169f519ce3c6a22d378f0b946c8178
https://bugzilla.redhat.com/show_bug.cgi?id=1198457
http://rhn.redhat.com/errata/RHSA-2015-0694.html
http://rhn.redhat.com/errata/RHSA-2015-0290.html
http://lists.opensuse.org/opensuse-security-announce/2015-04/msg00009.html