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

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Date:	Tue, 31 May 2016 12:49:07 -0400
From:	Lyude <cpaul@...hat.com>
To:	stable@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Lyude <cpaul@...hat.com>, David Airlie <airlied@...ux.ie>,
	dri-devel@...ts.freedesktop.org (open list:DRM DRIVERS),
	linux-kernel@...r.kernel.org (open list)
Subject: [PATCH 4/4] drm/atomic: Verify connector->funcs != NULL when clearing states

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@...ll.ch>
Signed-off-by: Lyude <cpaul@...hat.com>
---
 drivers/gpu/drm/drm_atomic.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
index 8ee1db8..d307d96 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;

 		/*
-- 
2.5.5