Does allocated memory make a module to be considered as "used" by the kernel

Question

I'm new to kernel programming, and currently working with the "Madwifi" driver for tplink wireless NIC (Atheros chipset). My kernel version is 2.6.32-37 (ubuntu).

I'm working with a driver which has been modified by other people (whom i don't know and can't contact to get more information) and i'm afraid they dynamically allocated memory (using kmalloc) but didn't free it appropriately.

My questions are:

1. If they actually did not free allocated memory, does it make the operating system to consider the module as "busy", making it unable to unload the module?

2. And how or where should i free allocated memory in modules (considering the fact that the module is supposed to run "forever")?

thanks!

omer.

Answer 1

No. Having allocated memory with kmalloc (or any of its colleagues) does not increment the use-count of a module. The ownership of allocated memory can change at any time just by passing the address (which is kept in a pointer-variable) to another module/block which store is somewhere. The kernel is not tracking this.

How memory is shared, given and taken depends a lot on the choice of coding-architecture and coding-model. This is written in C; there are no rules for that.

One way to handle the use-count of a module is to use kref. See for more information see Documentation/kref.txt in the kernel-source-tree or here.