I think there's a latent bug in a DRM error path, at least when used
by i915. In the scenario below, if dev->driver->bus->agp_init()
fails, we call drm_lastclose(). At least in i915_driver_lastclose(),
this dereferences dev->dev_private (at "1" below).
But dev->dev_private isn't initialized until "2", in i915_driver_load().
i915_pci_probe
drm_get_pci_dev
drm_fill_in_dev
drm_pci_agp_init (dev->driver->bus->agp_init)
drm_lastclose # error path when agp_init fails
i915_driver_lastclose (dev->driver->lastclose)
intel_fb_restore_mode
1)
drm_fb_helper_restore_fbdev_mode(&dev->dev_private->fbdev->helper)
i915_driver_load (dev->driver->load)
2) dev->dev_private = (void *)dev_priv
We tripped over this because a different bug caused drm_pci_agp_init()
to fail when it shouldn't have. Details about that bug are here:
https://bugzilla.kernel.org/show_bug.cgi?id=46481#c16
That bug has been fixed, but this dev_private initialization ordering
problem is still there, waiting to bite us again on the next machine
where drm_pci_agp_init() fails for some reason.
Bjorn
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