Reboot not calling module_exit of LKM

[Greg KH]

On Fri, Aug 05, 2011 at 11:39:16AM -0700, Ramesh.P wrote:
> 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?

Yes.

> b. If yes, what are the reasons? (One reason may be, not to get into
> new problems while cleaning up the module)

You don't need to unload a module as the machine is about to be turned
off.

> c. Is there anyway for the kernel module to know the system is getting
> rebooted? (Apart from letting userspace to indicate the kernel
> module).

Yes, hook to the reboot notifier.