Trying to grab dma_resv_lock while in commit_tail before we've done
all the code that leads to the eventual signalling of the vblank event
(which can be a dma_fence) is deadlock-y. Don't do that.
Here the solution is easy because just grabbing locks to read
something races anyway. We don't need to bother, READ_ONCE is
equivalent. And avoids the locking issue.
Cc: linux-media@xxxxxxxxxxxxxxx
Cc: linaro-mm-sig@xxxxxxxxxxxxxxxx
Cc: linux-rdma@xxxxxxxxxxxxxxx
Cc: amd-gfx@xxxxxxxxxxxxxxxxxxxxx
Cc: intel-gfx@xxxxxxxxxxxxxxxxxxxxx
Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Cc: Christian König <christian.koenig@xxxxxxx>
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
---
drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 10 ++++++++++
1 file changed, 10 insertions(+)
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 c575e7394d03..04c11443b9ca 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -6910,7 +6910,11 @@ static void amdgpu_dm_commit_planes(struct drm_atomic_state *state,
* explicitly on fences instead
* and in general should be called for
* blocking commit to as per framework helpers
+ *
+ * Yes, this deadlocks, since you're calling dma_resv_lock in a
+ * path that leads to a dma_fence_signal(). Don't do that.
*/
+#if 0
r = amdgpu_bo_reserve(abo, true);
if (unlikely(r != 0))
DRM_ERROR("failed to reserve buffer before flip\n");
@@ -6920,6 +6924,12 @@ static void amdgpu_dm_commit_planes(struct drm_atomic_state *state,
tmz_surface = amdgpu_bo_encrypted(abo);
amdgpu_bo_unreserve(abo);
+#endif
+ /*
+ * this races anyway, so READ_ONCE isn't any better or worse
+ * than the stuff above. Except the stuff above can deadlock.
+ */
+ tiling_flags = READ_ONCE(abo->tiling_flags);
fill_dc_plane_info_and_addr(
dm->adev, new_plane_state, tiling_flags,
--
2.26.2
