/usr/lib/dracut/modules.d/90dm/dm-pre-udev.sh is in dracut-core 047-2.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 | #!/bin/sh
strstr "$(cat /proc/misc)" device-mapper || modprobe dm_mod
modprobe dm_mirror 2>/dev/null
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