> -----Original Message-----
> From: amd-gfx <amd-gfx-boun...@lists.freedesktop.org> On Behalf Of
> Christian K?nig
> Sent: Saturday, March 30, 2019 2:33 AM
> To: amd-gfx@lists.freedesktop.org
> Subject: [PATCH] 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.koe...@amd.com>
> ---
> drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c | 24 ++++++++++++++++-
> ------
> 1 file 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))) {
Isn't this line redundant with dma_fence_get_rcu_safe? I think it's unnecessary.
Otherwise looks ok to me.
-David
> + 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;
> --
> 2.17.1
>
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