[PATCH] drm/amdgpu: fix user fence write race condition

[Nicolai Hähnle]

From: Nicolai Hähnle <nicolai.haehnle at amd.com>

The buffer object backing the user fence is reserved using the non-user
fence, i.e., as soon as the non-user fence is signaled, the user fence
buffer object can be moved or even destroyed.

Therefore, emit the user fence first.

Both fences have the same cache invalidation behavior, so this should
have no user-visible effect.

Signed-off-by: Nicolai Hähnle <nicolai.haehnle at amd.com>
---
There is one aspect to this change that I'm a bit unsure about: what does
insert_end do? It's only used by UVD & friends, and since those rings
don't use user fences I guess this patch doesn't really change anything
for them. And having the insert_end between those fences always looked
a bit suspicious...
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c
index 829c4d2a33b9..8117b8c2113e 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c
@@ -227,38 +227,38 @@ int amdgpu_ib_schedule(struct amdgpu_ring *ring, unsigned num_ibs,
 	if (ring->funcs->emit_tmz)
 		amdgpu_ring_emit_tmz(ring, false);
 
 	if (ring->funcs->emit_hdp_invalidate
 #ifdef CONFIG_X86_64
 	    && !(adev->flags & AMD_IS_APU)
 #endif
 	   )
 		amdgpu_ring_emit_hdp_invalidate(ring);
 
+	/* wrap the last IB with fence */
+	if (job && job->uf_addr) {
+		amdgpu_ring_emit_fence(ring, job->uf_addr, job->uf_sequence,
+				       AMDGPU_FENCE_FLAG_64BIT);
+	}
+
 	r = amdgpu_fence_emit(ring, f);
 	if (r) {
 		dev_err(adev->dev, "failed to emit fence (%d)\n", r);
 		if (job && job->vmid)
 			amdgpu_vmid_reset(adev, ring->funcs->vmhub, job->vmid);
 		amdgpu_ring_undo(ring);
 		return r;
 	}
 
 	if (ring->funcs->insert_end)
 		ring->funcs->insert_end(ring);
 
-	/* wrap the last IB with fence */
-	if (job && job->uf_addr) {
-		amdgpu_ring_emit_fence(ring, job->uf_addr, job->uf_sequence,
-				       AMDGPU_FENCE_FLAG_64BIT);
-	}
-
 	if (patch_offset != ~0 && ring->funcs->patch_cond_exec)
 		amdgpu_ring_patch_cond_exec(ring, patch_offset);
 
 	ring->current_ctx = fence_ctx;
 	if (vm && ring->funcs->emit_switch_buffer)
 		amdgpu_ring_emit_switch_buffer(ring);
 	amdgpu_ring_commit(ring);
 	return 0;
 }
 
-- 
2.14.1