Getting names of all kernel modules used by a particular module

Question

In the output of lsmod command, Used by column sometimes does not have the name of the kernel modules used by the module. For example, consider the following part-output of the lsmod command:

 Module                  Size  Used by
 xen_blkfront           16512  4 
 ext3                  137007  1 
 jbd                    54383  1 ext3
 mbcache                 7438  1 ext3

In the above output, ext3 module is used by 1 module, but its name is not there. Similarly, xen_blkfront module is used by 4 modules, but there are no names for those modules. But, jdb and mbcache modules are used by ext3 module. So, is there a way to get these missing module names ?

I need this because the kernel does not allow me to rmmod ext3 module saying "ERROR: Module ext3 is in use".

Answer 1

The "Used by" column shows not only the number of referencing modules, but the numer of times that any kernel code has taken a reference to the module.

For file systems and device drivers, this typically happens when a file/device is opened.

The source of those references is not tracked.