Re: [PATCH 16/18] io_uring: add support for IORING_OP_POLL

+	/* one for removal from waitqueue, one for this function */
+	refcount_set(&req->refs, 2);
+
+	mask = vfs_poll(poll->file, &ipt.pt) & poll->events;
+	if (unlikely(!poll->head)) {
+		/* we did not manage to set up a waitqueue, done */
+		goto out;
+	}
+
+	spin_lock_irq(&ctx->completion_lock);
+	spin_lock(&poll->head->lock);
+	if (poll->woken) {
+		/* wake_up context handles the rest */
+		mask = 0;
+		ipt.error = 0;
+	} else if (mask || ipt.error) {
+		/* if we get an error or a mask we are done */
+		WARN_ON_ONCE(list_empty(&poll->wait.entry));
+		list_del_init(&poll->wait.entry);
+	} else {
+		/* actually waiting for an event */
+		list_add_tail(&req->list, &ctx->cancel_list);
+	}
+	spin_unlock(&poll->head->lock);
+	spin_unlock_irq(&ctx->completion_lock);
+
+out:
+	if (unlikely(ipt.error)) {
+		if (!(flags & IOSQE_FIXED_FILE))
+			fput(poll->file);
+		return ipt.error;
+	}

+
+	if (mask)
+		io_poll_complete(req, mask);
+	io_free_req(req);
+	return 0;
+}