[Intel-gfx] [PATCH 4/4] drm/atomic: Verify connector->funcs != NULL when clearing states

[Lyude]

Unfortunately since we don't have Dave's connector refcounting patch
here yet, it's very possible that drm_atomic_state_default_clear() could
get called by intel_display_resume() when
intel_dp_mst_destroy_connector() isn't completely finished destroying an
mst connector, but has already finished setting connector->funcs to
NULL. As such, we need to treat the connector like it's already been
destroyed and just skip it, otherwise we'll end up dereferencing a NULL
pointer.

This fix is only required for 4.6 and below. David Airlie's patchseries
for 4.7 to add connector reference counting provides a more proper fix
for this.

Upstream fix: b164d31f50b2923a7a92c2a40cb46973a6ba8c36
Cc: stable at vger.kernel.org
Signed-off-by: Lyude <cpaul at redhat.com>
---
 drivers/gpu/drm/drm_atomic.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
index 8ee1db8..d3a5b5c 100644
--- a/drivers/gpu/drm/drm_atomic.c
+++ b/drivers/gpu/drm/drm_atomic.c
@@ -139,7 +139,7 @@ void drm_atomic_state_default_clear(struct drm_atomic_state *state)
 	for (i = 0; i < state->num_connector; i++) {
 		struct drm_connector *connector = state->connectors[i];
 
-		if (!connector)
+		if (!connector || !connector->funcs)
 			continue;
 
 		/*
@@ -150,6 +150,7 @@ void drm_atomic_state_default_clear(struct drm_atomic_state *state)
 		 * case by setting all connector pointers to NULL.
 		 */
 		state->connector_states[i]->connector = NULL;
+
 		connector->funcs->atomic_destroy_state(NULL,
 						       state->connector_states[i]);
 		state->connectors[i] = NULL;
-- 
2.5.5