I really wonder what's wrong with my mail client, but it looks like this patch never made it at least to dri-devel.

Forwarding manually now, Christian.

Am 04.09.2017 um 15:16 schrieb Christian König:

From: Christian König christian.koenig@amd.com

The logic is buggy and unnecessary complex. When dma_fence_get_rcu() fails to acquire a reference it doesn't necessary mean that there is no fence at all.

It usually mean that the fence was replaced by a new one and in this situation we certainly want to have the new one as result and *NOT* NULL.

Signed-off-by: Christian König christian.koenig@amd.com Cc: Chris Wilson chris@chris-wilson.co.uk Cc: Daniel Vetter daniel.vetter@ffwll.ch Cc: Sumit Semwal sumit.semwal@linaro.org Cc: linux-media@vger.kernel.org Cc: dri-devel@lists.freedesktop.org Cc: linaro-mm-sig@lists.linaro.org

---

include/linux/dma-fence.h | 23 ++--------------------- 1 file changed, 2 insertions(+), 21 deletions(-)

diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h index a5195a7..37f3d67 100644 --- a/include/linux/dma-fence.h +++ b/include/linux/dma-fence.h @@ -246,27 +246,8 @@ dma_fence_get_rcu_safe(struct dma_fence * __rcu *fencep) struct dma_fence *fence;

fence = rcu_dereference(*fencep);

• if (!fence || !dma_fence_get_rcu(fence))
  

• 	return NULL;
  

• /* The atomic_inc_not_zero() inside dma_fence_get_rcu()
  

•  * provides a full memory barrier upon success (such as now).
  

•  * This is paired with the write barrier from assigning
  

•  * to the __rcu protected fence pointer so that if that
  

•  * pointer still matches the current fence, we know we
  

•  * have successfully acquire a reference to it. If it no
  

•  * longer matches, we are holding a reference to some other
  

•  * reallocated pointer. This is possible if the allocator
  

•  * is using a freelist like SLAB_TYPESAFE_BY_RCU where the
  

•  * fence remains valid for the RCU grace period, but it
  

•  * may be reallocated. When using such allocators, we are
  

•  * responsible for ensuring the reference we get is to
  

•  * the right fence, as below.
  

•  */
  

• if (fence == rcu_access_pointer(*fencep))
  

• 	return rcu_pointer_handoff(fence);
  

• dma_fence_put(fence);
  

• if (!fence || dma_fence_get_rcu(fence))
  

• 	return fence;
  

  } while (1); }