Hi Janusz,
On Tue, Feb 11, 2025 at 01:12:37PM +0100, Janusz Krzysztofik wrote:
> On Monday, 10 February 2025 14:01:19 CET Andi Shyti wrote:
> > On Thu, Feb 06, 2025 at 07:07:38PM +0100, Janusz Krzysztofik wrote:
> > > We return immediately from i915_driver_register() if drm_dev_register()
> > > fails, skipping remaining registration steps. However, the _unregister()
> > > counterpart called at device remove knows nothing about that skip and
> > > executes reverts for all those steps. For that to work correctly, those
> > > revert functions must be resistant to being called even on uninitialized
> > > objects, or we must not skip their initialization.
> > >
> > > Three cases have been identified and fixes proposed. Call traces are
> > > taken from CI results of igt@i915_driver_load@reload-with-fault-injection
> > > execution, reported to several separate Gitlab issues (links provided).
> > >
> > > Immediate return was introduced to i915_driver_register() by commit
> > > ec3e00b4ee27 ("drm/i915: stop registering if drm_dev_register() fails"),
> > > however, quite a few things have changed since then. That's why I haven't
> > > mentioned it in a Fixes: tag to avoid it being picked up by stable, which
> > > I haven't tested.
> >
> > I'm not fully convinced about this series as I think that you are
> > fixing a subset of what needs to be handled properly. What about
> > hwmon? What about gt? what about debugfs?
>
> For all of those, their _unregister() functions seem to be designed to be safe
> to call even if not registered. Like e.g. kfree() -- you can call it safely
> even with NULL argument, you don't need to check for NULL and call it
> conditionally. However, ...
>
> >
> > In my opinion we need to check in _unregister whether the
> > drm_dev_register has succeded
>
> I agree with you that it would be more clear if we skipped not only
> _register() but also _unregister() steps symmetrically, based on result of
> drm_dev_register().
>
> > and one way would be, e.g., to
> > check for the drm minor value, or even set the drm device tu NULL
> > (first things that come to my mind, maybe there are smarter ways
> > of doing it).
>
> As long as drm doesn't provide explicit support for checking if registration
> succeeded other than examining the return value of drm_dev_register(), I would
> rather store that value somewhere in our drm_i915_private structure instead of
> depending on drm internals. What do you think?
yes, I think we could have a local flag.
Andi
> Thanks,
> Janusz
>
>
> > This way we could skip some of the _unregister()
> > steps.
> >
> > Andi
> >
>
>
>
