Need your assistance:

Currently I am using Wind River Linux distribution OS with kernel version 2.6.27.39 and Wind River version pne-3. After loading of my kernel module, I found it was permanent in the kernel using lsmod (for ex see below Ref 1). When I tried to remove, it was displaying as “ERROR: Removing 'hsl_module': Device or resource busy”. For your information, the same module is working fine with the Wind River pne-2 Linux Distribution OS with kernel version 2.6.21.

From the kernel source, I came to know that only possibility of showing permanent is “if there is non-availability of cleanup_module with the availability of init_module”.

But in my case, cleanup module also available in memory, after loading the module. I used to check using the file in /proc/kallsyms for the availability of cleanup module in memory.

Thanks for reading. Prompt reply is expected to identify the root cause.

Ref 1:
Module Size Used by
hsl_module 530454 0 [permanent]

Regards,
Sakthi

Please give us the output of `lsmod | grep hsl`? I think there are some kernel modules depend on it.

ENABLE force unloadiung in kernel and recompile ur kernel. use make menuconfig to go this option.

hsl module has some dependency on another modules. But, I am sure that there is no problem with dependency because I have done a sample module having the same instructions used in hsl init and cleanup module and its working fine. Currently I have doubts on Makefile and the compiler flags used. I had the thought that some optimization was done during compilation which lead to discarding of the cleanup module from the memory.

After more debugging, I have identified root cause for the problem. The problem is, in the executable file(.ko) created, does not have ".rela.init.text and .rela.exit.text" in section headers which are responsible for starting address of init module and cleanup module correspondingly, used by the kernel for linking and relocation during loading of kernel module. But still I am searching for solution because I don't know the exact flag to be specified during compilation to get those section headers.

For your information, I have used the command 'readelf -a <file>.ko' to get the headers and symbol table of the executable created.

Thanks for your suggestion. Finally, I identified the solution for the permanent issued I faced after loading my kernel module. The solution is the kernel macro; 'USE_IMMEDIATE' has to be defined (to be given as -DUSE_IMMEDIATE along with compiler flags) during compilation of my module. Actually, I don't know much deep about the usage of this kernel macro and how it resolves the issue, but one thing I came to know that it was used during module relocation while inserting the module. If anyone help me to get know much about it, then it will be fine. Also, for your information, I have used my own Makefile for compilation of kernel loadable modules. So, I have to add myself this macro to get rid of this permanent issue. Another fine solution is, you can make use of kernel build Makefile itself (if linux kernel version is above 2.4) to build your kernel loadable modules. Because it itself include all default macros and flags needed for compilation of your module. I have specified below the sample Makefile for compiling kernel loadable modules with kernel build Makefile.
Reference:
obj-m += hello.o
all:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
clean:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

Regards,
Sakthi Selvam