Is there a way to figure out what is using a Linux kernel module?

Question

If I load a kernel module and list the loaded modules with lsmod, I can get the "use count" of the module (number of other modules with a reference to the module). Is there a way to figure out what is using a module, though?

The issue is that a module I am developing insists its use count is 1 and thus I cannot use rmmod to unload it, but its "by" column is empty. This means that every time I want to re-compile and re-load the module, I have to reboot the machine (or, at least, I can't figure out any other way to unload it).

user_46192 · Answer

It says on the Linux Kernel Module Programming Guide that the use count of a module is controlled by the functions try_module_get and module_put. Perhaps you can find where these functions are called for your module.

More info: https://www.kernel.org/doc/htmldocs/kernel-hacking/routines-module-use-counters.html

Norman_Ramsey_41661 · Answer

All you get are a list of which modules depend on which other modules (the Used by column in lsmod). You can't write a program to tell why the module was loaded, if it is still needed for anything, or what might break if you unload it and everything that depends on it.

user_54322 · Answer

You might try lsof or fuser.

user_2969435 · Answer

If you use rmmod WITHOUT the --force option, it will tell you what is using a module. Example:

$ lsmod | grep firewire
firewire_ohci          24695  0 
firewire_core          50151  1 firewire_ohci
crc_itu_t               1717  1 firewire_core

$ sudo modprobe -r firewire-core
FATAL: Module firewire_core is in use.

$ sudo rmmod firewire_core
ERROR: Module firewire_core is in use by firewire_ohci

$ sudo modprobe -r firewire-ohci
$ sudo modprobe -r firewire-core
$ lsmod | grep firewire
$

user_1011932 · Answer

try kgdb and set breakpoint to your module

Is there a way to figure out what is using a Linux kernel module?

7 Answers