Hello, there seems to be a problem with device attach sequence offered by newbus. Basically, when device attach method is executing, device is not fully initialized yet. Also the device state in the newbus part of the world is DS_ALIVE. There is definitely no shattering news in the statements, but drivers that e.g. create devfs node to communicate with consumers are prone to a race.

If /dev node is created inside device attach method, then usermode can start calling cdevsw methods before device fully initialized itself. Even more, if device tries to use newbus helpers in cdevsw methods, like device_busy(9), then panic occurs "called for unatteched device". I get reports from users about this issues, to it is not something that only could happen.

I propose to add DEVICE_AFTER_ATTACH() driver method, to be called from newbus right after device attach finished and newbus considers the device fully initialized. Driver then could create devfs node in the after_attach method instead of attach. Please see the patch below.