From cpaul@redhat.com  Sat Jun  4 13:44:11 2016
From: Lyude <cpaul@redhat.com>
Date: Tue, 31 May 2016 12:49:07 -0400
Subject: drm/atomic: Verify connector->funcs != NULL when clearing states
To: stable@vger.kernel.org, Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Lyude <cpaul@redhat.com>, David Airlie <airlied@linux.ie>, dri-devel@lists.freedesktop.org (open list:DRM DRIVERS), linux-kernel@vger.kernel.org (open list)
Message-ID: <1464713347-28982-5-git-send-email-cpaul@redhat.com>

From: Lyude <cpaul@redhat.com>

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.

Changes since v1:
 - Fix leftover whitespace

Upstream fix: 0552f7651bc2 ("drm/i915/mst: use reference counted
connectors. (v3)")
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Lyude <cpaul@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/gpu/drm/drm_atomic.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/gpu/drm/drm_atomic.c
+++ b/drivers/gpu/drm/drm_atomic.c
@@ -139,7 +139,7 @@ void drm_atomic_state_default_clear(stru
 	for (i = 0; i < state->num_connector; i++) {
 		struct drm_connector *connector = state->connectors[i];
 
-		if (!connector)
+		if (!connector || !connector->funcs)
 			continue;
 
 		/*