Merge tag 'for-linus-2021-03-10' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux

Pull detached mounts fix from Christian Brauner:
 "Creating a series of detached mounts, attaching them to the
  filesystem, and unmounting them can be used to trigger an integer
  overflow in ns->mounts causing the kernel to block any new mounts in
  count_mounts() and returning ENOSPC because it falsely assumes that
  the maximum number of mounts in the mount namespace has been reached,
  i.e. it thinks it can't fit the new mounts into the mount namespace
  anymore.

  Without this fix heavy use of the new mount API with move_mount() will
  cause the host to become unuseable and thus blocks some xfstest
  patches I want to resend.

  Depending on the number of mounts in your system, this can be
  reproduced on any kernel that supportes open_tree() and move_mount().

  A reproducer has been sent for inclusion with xfstests. It takes care
  to do this in another mount namespace, not in the host's mount
  namesp...