[Intel-gfx] [PATCH v2] drm/i915: Cancel the hotplug work when unregistering the connector

[Chris Wilson]

Quoting Maarten Lankhorst (2017-10-09 11:33:21)
> Op 09-10-17 om 11:59 schreef Chris Wilson:
> > Quoting Maarten Lankhorst (2017-10-09 10:41:29)
> >> Op 06-10-17 om 19:18 schreef Chris Wilson:
> >>> When we unregister the connector, we may have a pending hotplug work.
> >>> This needs to be cancel early during the teardown so that it does not
> >>> fire after we have freed the connector. Or else we may see something like:
> >> Well the nice thing is even if it's called modeset_retry_work, it just sets the link status to bad for DP.
> > Ok, and sends a hotplug event. At what point in the shutdown sequence
> > does that drm_kms_helper_hotplug_event() become invalid?
> Some digging makes me suspect at the very end of driver unload. So for this either is fine. But after some more digging, it's not enough, see below.
> >> I worry it might be too early, wouldn't intel_dp_connector_destroy be a better place? At that point we know userspace can no longer use it,
> >> because the last reference has been removed.
> > connector_destroy is after drm_kms_helper_poll_fini(), so that seems
> > suspect given a query about drm_kms_helper_hotplug_event()
> >
> > A hook from drm_atomic_helper_shutdown? Extending unregister to have a
> > late phase?
> >
> Well after some more digging the only case where early_unregister vs unregister matters is DP-MST, where we can lose connectors dynamically.
> As long as we never use modeset_retry_work on DP-MST connectors, everything is fine. Fortunately we don't do that, only used in DP connectors for now.
> 
> But if you look at the backtrace, the first error is from intel_fbdev_fini, so we need to cancel the work after poll_fini, and before fbdev_fini.
> 
> Fixing it in early_unregister is simply too late..

early_unregister is before fbdev_fini. You may mean that it's too early?

Anyway, shall we just revert

commit 9301397a63b3bf1090dffe846c6f1c8efa032236
Author: Manasi Navare <manasi.d.navare at intel.com>
Date:   Thu Apr 6 16:44:19 2017 +0300

    drm/i915: Implement Link Rate fallback on Link training failure

as the authors seem not to care about the kernel oopses?
-Chris