From: Christian König <christian.koenig@xxxxxxx> 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 at amd.com> Cc: Chris Wilson <chris at chris-wilson.co.uk> Cc: Daniel Vetter <daniel.vetter at ffwll.ch> Cc: Sumit Semwal <sumit.semwal at linaro.org> Cc: linux-media at vger.kernel.org Cc: dri-devel at lists.freedesktop.org Cc: linaro-mm-sig at 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); } -- 2.7.4
