From: Christian König christian.koenig@amd.com
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.
v2: Keep extra check after dma_fence_get_rcu().
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 | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h index 0a186c4..f4f23cb 100644 --- a/include/linux/dma-fence.h +++ b/include/linux/dma-fence.h @@ -248,9 +248,12 @@ 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)) + if (!fence) return NULL;
+ if (!dma_fence_get_rcu(fence)) + continue; + /* 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
Op 15-09-17 om 11:53 schreef Christian König:
From: Christian König christian.koenig@amd.com
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.
v2: Keep extra check after dma_fence_get_rcu().
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 | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h index 0a186c4..f4f23cb 100644 --- a/include/linux/dma-fence.h +++ b/include/linux/dma-fence.h @@ -248,9 +248,12 @@ 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))
if (!fence) return NULL;
if (!dma_fence_get_rcu(fence))continue;- /* 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
Should be safe from an infinite loop since the old fence is only unreffed after the new pointer is written, so we'll always make progress. :)
Reviewed-by: Maarten Lankhorst maarten.lankhorst@linux.intel.com
linaro-mm-sig@lists.linaro.org
-
Christian König -
Maarten Lankhorst