On Thu, Apr 12, 2018 at 03:42:32PM +0100, Ayan Kumar Halder wrote:
> In a situation when the reference count of the drm connector is greater than
> the unbind function should not invoke drm_connector_cleanup as this will lead
> to an inconsistent state where the drm_crtc_state->connector_mask still has
> a bitmask referring to the stale connector. Later, when drm driver invokes
> drm_atomic_helper_shutdown() which invokes --->
> ---> drm_atomic_commit() --> drm_atomic_check_only() -->
> drm_atomic_helper_check() --> drm_atomic_helper_check_modeset(). This returns
> an error due to enabled/connectors mismatch.
> In such a scenario, one should just return from _unbind() and let the drm
> subsequently invoke drm_atomic_helper_shutdown. This will reset the
> drm_crtc_state->connector_mask and will shutdown the crtcs. It will also
> the reference count of the connectors to 1. Subsequently,
> will get invoked which will do the following :-
If the device is still in-use after unbind() has been called, that is
_very_ bad news, and probably means that the "host" driver is not
calling component_unbind() at the right point.
Any resources claimed in the bind() callback using devm functions
will be freed, which will include (eg) the drm_encoder structure and
in fact the drm_connector. So what you have here is a use-after-free
bug, and your change does nothing for that.
Please fix the "host" driver instead.
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