Reboot not calling module_exit of LKM

Hi,

Good day!

When a system is rebooted, the loadable kernel modules 'module_exit'
functions are not called. I see this behavior in a custom kernel. My
questions are

a. Is this applicable in mainline/normal kernel too?
b. If yes, what are the reasons? (One reason may be, not to get into
new problems while cleaning up the module)
c. Is there anyway for the kernel module to know the system is getting
rebooted? (Apart from letting userspace to indicate the kernel
module).

Appreciate your help and apologize if this is already answered in this forum.

Thanks,
Ramesh