[PATCH] drm/amd/display: Fix deadlock with display during hanged ring recovery.

[Andrey Grodzovsky]

When ring hang happens amdgpu_dm_commit_planes during flip is holding
the BO reserved and then stack waiting for fences to signal in
reservation_object_wait_timeout_rcu (which won't signal because there
was a hnag). Then when we try to shutdown display block during reset
recovery from drm_atomic_helper_suspend we also try to reserve the BO
from dm_plane_helper_cleanup_fb ending in deadlock.
Also remove useless WARN_ON

Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky at amd.com>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index acc4ff8..f8dec36 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -4802,14 +4802,21 @@ static void amdgpu_dm_commit_planes(struct drm_atomic_state *state,
 			 */
 			abo = gem_to_amdgpu_bo(fb->obj[0]);
 			r = amdgpu_bo_reserve(abo, true);
-			if (unlikely(r != 0)) {
+			if (unlikely(r != 0))
 				DRM_ERROR("failed to reserve buffer before flip\n");
-				WARN_ON(1);
-			}
 
-			/* Wait for all fences on this FB */
-			WARN_ON(reservation_object_wait_timeout_rcu(abo->tbo.resv, true, false,
-										    MAX_SCHEDULE_TIMEOUT) < 0);
+			/*
+			 * Wait for all fences on this FB. Do limited wait to avoid
+			 * deadlock during GPU reset when this fence will not signal
+			 * but we hold reservation lock for the BO.
+			 */
+			r = reservation_object_wait_timeout_rcu(abo->tbo.resv,
+								true, false,
+								msecs_to_jiffies(5000));
+			if (unlikely(r == 0))
+				DRM_ERROR("Waiting for fences timed out.");
+
+
 
 			amdgpu_bo_get_tiling_flags(abo, &tiling_flags);
 
-- 
2.7.4