ras-urgent-2020-02-22

  - Populate the per CPU MCA bank descriptor pointer only after it has been
    completely set up to prevent a use-after-free in case that one of the
    subsequent initialization step fails

  - Implement a proper release function for the sysfs entries of MCA
    threshold controls instead of freeing the memory right in the CPU
    teardown code, which leads to another use-after-free when the
    associated sysfs file is opened and accessed.