ioctl_by_bdev may only be used INSIDE the kernel.  If the "arg" argument
refers to memory that is accessed by put_user/get_user in the ioctl
function, the memory needs to be in the kernel address space (that's the
set_fs(KERNEL_DS) doing in the ioctl_by_bdev).  This works on i386 because
even with set_fs(KERNEL_DS) the user space memory is still accessible with
put_user/get_user.  That is not true for s390.  In short the ioctl
implementation of the pktcdvd device driver is horribly broken.
Signed-off-by: Peter Osterlund <petero2@telia.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>