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).

Answer 1

You might try lsof or fuser.

Answer 2

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.

Answer 3

rmmod has a --force parameter. If you know the stuff your module does, and have a kernel configured to support forcing unload, that might work. That's to save you from having to restart until you fixed the problem with the ref-counting), but it won't show you the cause of the load of your module. I think it's not possible to get why the module was loaded in the first place (i.e which exact code-path). Maybe dmesg has logged something useful or you can add some useful logging into your module code.

Answer 4

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 try_module_put. Perhaps you can find where these functions are called for your module.