drm/atomic: Handle -EDEADLK with out-fences correctly

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@collabora.co.uk>
Cc: Brian Starkey <brian.starkey@arm.com> (v10)
Cc: Sean Paul <seanpaul@chromium.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: David Airlie <airlied@linux.ie>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: <stable@vger.kernel.org> # v4.10+
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@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> #intel-gfx on irc

1 files changed, 4 insertions, 2 deletions

diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
index c0f336d23f9c..b43939f24812 100644
--- a/drivers/gpu/drm/drm_atomic.c
+++ b/drivers/gpu/drm/drm_atomic.c
@@ -2167,10 +2167,10 @@ 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))
@@ -2211,6 +2211,8 @@ 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;