[PATCH] drm/atomic: Handle -EDEADLK with out-fences correctly

[Maarten Lankhorst]

complete_crtc_signaling is freeing fence_state, but when retrying
num_fences and fence_state are not zero'd. This caused duplicate
fd's in the fence_state array, followed by a BUG_ON in fs/file.c
because we reallocate freed memory, and installing over an existing
fd, or potential other fun.

Zero fence_state and num_fences correctly in the retry loop, which
allows kms_atomic_transition to pass.

Fixes: beaf5af48034 ("drm/fence: add out-fences support")
Cc: Gustavo Padovan <gustavo.padovan at collabora.co.uk>
Cc: Brian Starkey <brian.starkey at arm.com> (v10)
Cc: Sean Paul <seanpaul at chromium.org>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Jani Nikula <jani.nikula at linux.intel.com>
Cc: David Airlie <airlied at linux.ie>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Cc: <stable at vger.kernel.org> # v4.10+
Testcase: kms_atomic_transitions.plane-all-modeset-transition-fencing
(with CONFIG_DEBUG_WW_MUTEX_SLOWPATH=y)
---
 drivers/gpu/drm/drm_atomic.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
index 1b755439f591..8ec9be4f5d50 100644
--- a/drivers/gpu/drm/drm_atomic.c
+++ b/drivers/gpu/drm/drm_atomic.c
@@ -2203,10 +2203,10 @@ int drm_mode_atomic_ioctl(struct drm_device *dev,
 	struct drm_atomic_state *state;
 	struct drm_modeset_acquire_ctx ctx;
 	struct drm_plane *plane;
-	struct drm_out_fence_state *fence_state = NULL;
+	struct drm_out_fence_state *fence_state;
 	unsigned plane_mask;
 	int ret = 0;
-	unsigned int i, j, num_fences = 0;
+	unsigned int i, j, num_fences;
 
 	/* disallow for drivers not supporting atomic: */
 	if (!drm_core_check_feature(dev, DRIVER_ATOMIC))
@@ -2247,6 +2247,8 @@ int drm_mode_atomic_ioctl(struct drm_device *dev,
 	plane_mask = 0;
 	copied_objs = 0;
 	copied_props = 0;
+	fence_state = NULL;
+	num_fences = 0;
 
 	for (i = 0; i < arg->count_objs; i++) {
 		uint32_t obj_id, count_props;
-- 
2.11.0