From: Lucas De Marchi > Sent: 13 March 2020 16:23 > On Wed, Mar 11, 2020 at 6:33 AM Konstantin Kharlamov <hi-angel@xxxxxxxxx> wrote: > > > > Once in a while there's a need to remove a module (for example because you rebuilt it, or to reload > it with different parameters, or whatever…). And then doing `rmmod modulename` and `modprobe -r > modulename` gives: > > > > rmmod: ERROR: Module modulename is in use > > > > If you're lucky, firing up `lsmod | grep modulename` will get you offenders inside "used by" column. > But often there's nothing except the count above zero. It is very easy to reproduce if you check > `lsmod` output for your graphics driver. I checked it on `i915` and `amdgpu`: when graphics session is > opened you can't remove it and `lsmod` doesn't show who's using it. > > > > There's very popular and old question on SO¹ that at the moment has over 55k views, and the only > answer that seem to work for people is insanely big and convoluted; it is using a custom kernel driver > and kernel tracing capabilities. I guess this amount of research means: no, currently there's no easy > way to get who's using a module. > > > > It would be amazing if kernel has capability to figure out who's using a module. > > Yeah, right now this would need some work on the kernel side to record > the callers of try_module_get()/__module_get()... usually done e.g on > fops-like structs in a owner field. > The only thing we have there right now is the trace. The trace is not > so bad since it can be added in the kernel command line, but would > usually only be enabled while debugging. > > For implementing such a feature I think we would need to add/remove > module owner into the mod struct whenever we have a _get()/_put(). > Maybe it's worth it, but it doesn't > come without overhead. I'd like to hear what other people think. Related would be a standard entry point into a module that indicates that someone would like to unload it. This would let the module code either error the request (EBUSY) or start a tidy up sequence that should make it possible to unload the module sometime later. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
