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SubjectRe: [PATCH v5 net-next 6/6] net: ethernet: ti: cpsw: add XDP support
On Mon, Jul 01, 2019 at 06:19:01PM +0200, Jesper Dangaard Brouer wrote:
>On Sun, 30 Jun 2019 20:23:48 +0300
>Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org> wrote:
>
>> +static int cpsw_ndev_create_xdp_rxq(struct cpsw_priv *priv, int ch)
>> +{
>> + struct cpsw_common *cpsw = priv->cpsw;
>> + int ret, new_pool = false;
>> + struct xdp_rxq_info *rxq;
>> +
>> + rxq = &priv->xdp_rxq[ch];
>> +
>> + ret = xdp_rxq_info_reg(rxq, priv->ndev, ch);
>> + if (ret)
>> + return ret;
>> +
>> + if (!cpsw->page_pool[ch]) {
>> + ret = cpsw_create_rx_pool(cpsw, ch);
>> + if (ret)
>> + goto err_rxq;
>> +
>> + new_pool = true;
>> + }
>> +
>> + ret = xdp_rxq_info_reg_mem_model(rxq, MEM_TYPE_PAGE_POOL,
>> + cpsw->page_pool[ch]);
>> + if (!ret)
>> + return 0;
>> +
>> + if (new_pool) {
>> + page_pool_free(cpsw->page_pool[ch]);
>> + cpsw->page_pool[ch] = NULL;
>> + }
>> +
>> +err_rxq:
>> + xdp_rxq_info_unreg(rxq);
>> + return ret;
>> +}
>
>Looking at this, and Ilias'es XDP-netsec error handling path, it might
>be a mistake that I removed page_pool_destroy() and instead put the
>responsibility on xdp_rxq_info_unreg().
As for me this is started not from page_pool_free, but rather from calling
unreg_mem_model from rxq_info_unreg. Then, if page_pool_free is hidden
it looks more a while normal to move all chain to be self destroyed.

>
>As here, we have to detect if page_pool_create() was a success, and then
>if xdp_rxq_info_reg_mem_model() was a failure, explicitly call
>page_pool_free() because the xdp_rxq_info_unreg() call cannot "free"
>the page_pool object given it was not registered.
Yes, it looked a little bit ugly from the beginning, but, frankly,
I have got used to this already.

>
>Ivan's patch in[1], might be a better approach, which forced all
>drivers to explicitly call page_pool_free(), even-though it just
>dec-refcnt and the real call to page_pool_free() happened via
>xdp_rxq_info_unreg().
>
>To better handle error path, I would re-introduce page_pool_destroy(),
So, you might to do it later as I understand, and not for my special
case but becouse it makes error path to look a little bit more pretty.
I'm perfectly fine with this, and better you add this, for now my
implementation requires only "xdp: allow same allocator usage" patch,
but if you insist I can resend also patch in question afterwards my
series is applied (with modification to cpsw & netsec & mlx5 & page_pool).

What's your choice? I can add to your series patch needed for cpsw to
avoid some misuse.

>as a driver API, that would gracefully handle NULL-pointer case, and
>then call page_pool_free() with the atomic_dec_and_test(). (It should
>hopefully simplify the error handling code a bit)
>
>[1] https://lore.kernel.org/netdev/20190625175948.24771-2-ivan.khoronzhuk@linaro.org/
>
>
>> +void cpsw_ndev_destroy_xdp_rxqs(struct cpsw_priv *priv)
>> +{
>> + struct cpsw_common *cpsw = priv->cpsw;
>> + struct xdp_rxq_info *rxq;
>> + int i;
>> +
>> + for (i = 0; i < cpsw->rx_ch_num; i++) {
>> + rxq = &priv->xdp_rxq[i];
>> + if (xdp_rxq_info_is_reg(rxq))
>> + xdp_rxq_info_unreg(rxq);
>> + }
>> +}
>
>Are you sure you need to test xdp_rxq_info_is_reg() here?
Yes it's required in my case as it's used in error path where
an rx queue can be even not registered and no need in this warn.

>
>You should just call xdp_rxq_info_unreg(rxq), if you know that this rxq
>should be registered. If your assumption failed, you will get a
>WARNing, and discover your driver level bug. This is one of the ways
>the API is designed to "detect" misuse of the API. (I found this
>rather useful, when I converted the approx 12 drivers using this
>xdp_rxq_info API).
>
>--
>Best regards,
> Jesper Dangaard Brouer
> MSc.CS, Principal Kernel Engineer at Red Hat
> LinkedIn: http://www.linkedin.com/in/brouer

--
Regards,
Ivan Khoronzhuk

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