Quoting Christian König (2017-09-04 14:27:33) > 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. Which is not guaranteed by the code you wrote either. The point of the comment is that the mb is only inside the successful kref_atomic_inc_unless_zero, and that only after that mb do you know whether or not you have the current fence. You can argue that you want to replace the if (!dma_fence_get_rcu()) return NULL with if (!dma_fence_get_rcu() continue; but it would be incorrect to say that by simply ignoring the post-condition check that you do have the right fence. -Chris
