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.khoronz...@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 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.
>
> 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().
We did discuss that xdp_XXXXX naming might be confusing.
That being said since Ivan's approach serves 'special' hardware and fixes the
naming irregularity, i perfectly fine doing that as long as we clearly document
that the API is supposed to serve a pool per queue (unless the hardware needs to
deal with it differently)
>
> To better handle error path, I would re-introduce page_pool_destroy(),
> 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.khoronz...@linaro.org/
>
>
Thanks
/Ilias
> > +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?
>
> 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
