How to prevent a module from unloading when in used

[Chetan Nanda]

On Wed, Jul 16, 2014 at 9:51 PM, Greg KH <greg at kroah.com> wrote:

> On Wed, Jul 16, 2014 at 08:57:38PM +0530, Chetan Nanda wrote:
> >
> >
> >
> > On Wed, Jul 16, 2014 at 8:49 PM, Chetan Nanda <chetannanda at gmail.com>
> wrote:
> >
> >
> >
> >     On Wed, Jul 16, 2014 at 6:39 PM, John de la Garza <john at 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?
>
> Never use try_module_get(), that is racy.
>
> What is the user/kernel interface you are using, and why doesn't it
> automatically increase the module count when userspace opens the
> interface?  It should all be done in a way that your module doesn't need
> to do anything special.
>
> Hi Greg,

Thanks for your mail.

Module is using misc driver interface to export its functionality to
userspace,

Need to debug further why module count is not getting incremented
automatically when module is open by userspace application via open system
call.

Thanks
Chetan Nanda

thanks,
>
> greg k-h
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.kernelnewbies.org/pipermail/kernelnewbies/attachments/20140718/2b89b52e/attachment.html