Re: [RFC PATCH] fpga: remove module reference counting from core components

Xu Yilun
2023-11-09T07:18:05Z

On Thu, Nov 09, 2023 at 06:27:24AM +0100, Greg Kroah-Hartman wrote:
> On Thu, Nov 09, 2023 at 01:07:42PM +0800, Xu Yilun wrote:
> > On Wed, Nov 08, 2023 at 05:20:53PM +0100, Greg Kroah-Hartman wrote:
> > > On Wed, Nov 08, 2023 at 11:52:52PM +0800, Xu Yilun wrote:
> > > > > >>
> > > > > >> In fpga_region_get() / fpga_region_put(): call get_device() before
> > > > > >> acquiring the mutex and put_device() after having released the mutex
> > > > > >> to avoid races.
> > >
> > > Why do you need another reference count with a lock? You already have
> > > that with the calls to get/put_device().
> >
> > The low-level driver module could still be possibly unloaded at the same
> > time, if so, when FPGA core run some callbacks provided by low-level driver
> > module, its referenced page of code is unmapped...
>
> Then something is designed wrong here, the unloading of the low-level
> driver should remove the access to the device itself. Perhaps fix that?

Actually the low-level driver module on its own has no way to garantee its
own code page of callbacks not accessed. It *is* accessing its code page
when it tries (to release) any protection.

Core code must help, and something like file_operations.owner is an
effective way.

Thanks,
Yilun