On Wed, Jul 16, 2014 at 8:49 PM, Chetan Nanda <chetannanda@gmail.com> wrote:

On Wed, Jul 16, 2014 at 6:39 PM, John de la Garza <john@jjdev.com> wrote:

On Wed, Jul 16, 2014 at 04:00:18PM +0530, Chetan Nanda wrote:
> A depends on B, so B is automatically loaded when A is loaded.
> B module is also directly being used by the user side code via misc
> interface.

>.

> Now when I am unloading module A, via "modprobe -r A" it is also unloading
> the module B which is being used by the application and resulting in the
> kernel crash.

You said that A depends on B, right? Why do you have A dependng on B?
If it A needs to have B then it makes sense that you can not remove A while
B is in use. If A doesn't need B, why not remove the dependency.

A is calling few APIs defined by B.

But why when user space application is already using module B. (it has already open its device fd) kernel allows to remove it.

I tried with doing try_module_get() in the module's open function, it prevent module B unloading but cause thread doing modprobe -r to hang

Is there any other way to mark module as busy when being used by user application?