[PATCH 4.12 56/99] drm/atomic: Handle -EDEADLK with out-fences correctly

[Greg Kroah-Hartman]

4.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>

commit 7f5d6dac548b983702dd7aac1d463bd88dff50a8 upstream.

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@xxxxxxxxxxxxxxx>
Cc: Brian Starkey <brian.starkey@xxxxxxx> (v10)
Cc: Sean Paul <seanpaul@xxxxxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
Cc: David Airlie <airlied@xxxxxxxx>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Testcase: kms_atomic_transitions.plane-all-modeset-transition-fencing
(with CONFIG_DEBUG_WW_MUTEX_SLOWPATH=y)
Link: https://patchwork.freedesktop.org/patch/msgid/20170814100721.13340-1-maarten.lankhorst@xxxxxxxxxxxxxxx
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx> #intel-gfx on irc
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/gpu/drm/drm_atomic.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/drm_atomic.c
+++ b/drivers/gpu/drm/drm_atomic.c
@@ -2093,10 +2093,10 @@ int drm_mode_atomic_ioctl(struct drm_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))
@@ -2137,6 +2137,8 @@ retry:
 	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;