drm/amdgpu: fix old fence check in amdgpu_fence_emit

We don't hold a reference to the old fence, so it can go away
any time we are waiting for it to signal.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Chunming Zhou <david1.zhou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

1 files changed, 17 insertions, 7 deletions

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
index ee47c11e92ce..4dee2326b29c 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
@@ -136,8 +136,9 @@ int amdgpu_fence_emit(struct amdgpu_ring *ring, struct dma_fence **f,
 {
         struct amdgpu_device *adev = ring->adev;
         struct amdgpu_fence *fence;
-        struct dma_fence *old, **ptr;
+        struct dma_fence __rcu **ptr;
         uint32_t seq;
+        int r;
 
         fence = kmem_cache_alloc(amdgpu_fence_slab, GFP_KERNEL);
         if (fence == NULL)
@@ -153,15 +154,24 @@ int amdgpu_fence_emit(struct amdgpu_ring *ring, struct dma_fence **f,
                                seq, flags | AMDGPU_FENCE_FLAG_INT);
 
         ptr = &ring->fence_drv.fences[seq & ring->fence_drv.num_fences_mask];
+        if (unlikely(rcu_dereference_protected(*ptr, 1))) {
+                struct dma_fence *old;
+
+                rcu_read_lock();
+                old = dma_fence_get_rcu_safe(ptr);
+                rcu_read_unlock();
+
+                if (old) {
+                        r = dma_fence_wait(old, false);
+                        dma_fence_put(old);
+                        if (r)
+                                return r;
+                }
+        }
+
         /* This function can't be called concurrently anyway, otherwise
          * emitting the fence would mess up the hardware ring buffer.
          */
-        old = rcu_dereference_protected(*ptr, 1);
-        if (old && !dma_fence_is_signaled(old)) {
-                DRM_INFO("rcu slot is busy\n");
-                dma_fence_wait(old, false);
-        }
-
         rcu_assign_pointer(*ptr, dma_fence_get(&fence->base));
 
         *f = &fence->base;