Quoting Christian König (2019-08-05 16:45:54)
> @@ -214,16 +214,16 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
> return 0;
>
> retry:
> - seq = read_seqcount_begin(&resv->seq);
> rcu_read_lock();
>
> + fence_excl = rcu_dereference(resv->fence_excl);
> fobj = rcu_dereference(resv->fence);
> if (fobj)
> shared_count = fobj->shared_count;
> else
> shared_count = 0;
> - fence_excl = rcu_dereference(resv->fence_excl);
> - if (read_seqcount_retry(&resv->seq, seq)) {
> +
> + if (rcu_dereference(resv->fence_excl) != fence_excl) {
If I remember my rules correctly, rcu_dereference is a
read-data-depends, which only means that a read through the pointer
returned by rcu_dereference() is after the retrieval of that pointer.
Nothing orders the retrieval of fence_excl vs shared_count (different
pointers), so I think the last line should be:
smp_rmb();
if (rcu_access_pointer(resv->fence_excl) != fence_excl)
-Chris
