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SubjectRe: [PATCH v7 net-next 1/5] net: core: page_pool: add user refcnt and reintroduce page_pool_destroy

CC: Tariq + Saeed, could you please review the mlx5 part.

On Fri, 5 Jul 2019 02:14:02 +0300
Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org> wrote:

> Jesper recently removed page_pool_destroy() (from driver invocation)
> and moved shutdown and free of page_pool into xdp_rxq_info_unreg(),
> in-order to handle in-flight packets/pages. This created an asymmetry
> in drivers create/destroy pairs.
>
> This patch reintroduce page_pool_destroy and add page_pool user
> refcnt. This serves the purpose to simplify drivers error handling as
> driver now drivers always calls page_pool_destroy() and don't need to
> track if xdp_rxq_info_reg_mem_model() was unsuccessful.
>
> This could be used for a special cases where a single RX-queue (with a
> single page_pool) provides packets for two net_device'es, and thus
> needs to register the same page_pool twice with two xdp_rxq_info
> structures.
>
> This patch is primarily to ease API usage for drivers. The recently
> merged netsec driver, actually have a bug in this area, which is
> solved by this API change.
>
> This patch is a modified version of Ivan Khoronzhu's original patch.
>
> Link: https://lore.kernel.org/netdev/20190625175948.24771-2-ivan.khoronzhuk@linaro.org/
> Fixes: 5c67bf0ec4d0 ("net: netsec: Use page_pool API")
> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
> Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
> Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>

Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>

Thank you Ivan for taking this more simple approach. If we later see
more drivers wanting this feature of a single RX-queue providing
packets to multiple net_device'es, then we can change into your
more generic API at XDP-reg-layer approach later. For now, we keep
code complexity as low as possible.


> ---
> .../net/ethernet/mellanox/mlx5/core/en_main.c | 4 +--
> drivers/net/ethernet/socionext/netsec.c | 8 ++----
> include/net/page_pool.h | 25 +++++++++++++++++++
> net/core/page_pool.c | 8 ++++++
> net/core/xdp.c | 3 +++
> 5 files changed, 40 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> index 2f9093ba82aa..ac882b2341d0 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> @@ -575,8 +575,6 @@ static int mlx5e_alloc_rq(struct mlx5e_channel *c,
> }
> err = xdp_rxq_info_reg_mem_model(&rq->xdp_rxq,
> MEM_TYPE_PAGE_POOL, rq->page_pool);
> - if (err)
> - page_pool_free(rq->page_pool);
> }
> if (err)
> goto err_free;
> @@ -644,6 +642,7 @@ static int mlx5e_alloc_rq(struct mlx5e_channel *c,
> if (rq->xdp_prog)
> bpf_prog_put(rq->xdp_prog);
> xdp_rxq_info_unreg(&rq->xdp_rxq);
> + page_pool_destroy(rq->page_pool);
> mlx5_wq_destroy(&rq->wq_ctrl);
>
> return err;
> @@ -678,6 +677,7 @@ static void mlx5e_free_rq(struct mlx5e_rq *rq)
> }
>
> xdp_rxq_info_unreg(&rq->xdp_rxq);
> + page_pool_destroy(rq->page_pool);
> mlx5_wq_destroy(&rq->wq_ctrl);
> }
>
> diff --git a/drivers/net/ethernet/socionext/netsec.c b/drivers/net/ethernet/socionext/netsec.c
> index 5544a722543f..43ab0ce90704 100644
> --- a/drivers/net/ethernet/socionext/netsec.c
> +++ b/drivers/net/ethernet/socionext/netsec.c
> @@ -1210,15 +1210,11 @@ static void netsec_uninit_pkt_dring(struct netsec_priv *priv, int id)
> }
> }
>
> - /* Rx is currently using page_pool
> - * since the pool is created during netsec_setup_rx_dring(), we need to
> - * free the pool manually if the registration failed
> - */
> + /* Rx is currently using page_pool */
> if (id == NETSEC_RING_RX) {
> if (xdp_rxq_info_is_reg(&dring->xdp_rxq))
> xdp_rxq_info_unreg(&dring->xdp_rxq);
> - else
> - page_pool_free(dring->page_pool);
> + page_pool_destroy(dring->page_pool);
> }
>
> memset(dring->desc, 0, sizeof(struct netsec_desc) * DESC_NUM);
> diff --git a/include/net/page_pool.h b/include/net/page_pool.h
> index ee9c871d2043..2cbcdbdec254 100644
> --- a/include/net/page_pool.h
> +++ b/include/net/page_pool.h
> @@ -101,6 +101,12 @@ struct page_pool {
> struct ptr_ring ring;
>
> atomic_t pages_state_release_cnt;
> +
> + /* A page_pool is strictly tied to a single RX-queue being
> + * protected by NAPI, due to above pp_alloc_cache. This
> + * refcnt serves purpose is to simplify drivers error handling.
> + */
> + refcount_t user_cnt;
> };
>
> struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp);
> @@ -134,6 +140,15 @@ static inline void page_pool_free(struct page_pool *pool)
> #endif
> }
>
> +/* Drivers use this instead of page_pool_free */
> +static inline void page_pool_destroy(struct page_pool *pool)
> +{
> + if (!pool)
> + return;
> +
> + page_pool_free(pool);
> +}
> +
> /* Never call this directly, use helpers below */
> void __page_pool_put_page(struct page_pool *pool,
> struct page *page, bool allow_direct);
> @@ -201,4 +216,14 @@ static inline bool is_page_pool_compiled_in(void)
> #endif
> }
>
> +static inline void page_pool_get(struct page_pool *pool)
> +{
> + refcount_inc(&pool->user_cnt);
> +}
> +
> +static inline bool page_pool_put(struct page_pool *pool)
> +{
> + return refcount_dec_and_test(&pool->user_cnt);
> +}
> +
> #endif /* _NET_PAGE_POOL_H */
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index b366f59885c1..3272dc7a8c81 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -49,6 +49,9 @@ static int page_pool_init(struct page_pool *pool,
>
> atomic_set(&pool->pages_state_release_cnt, 0);
>
> + /* Driver calling page_pool_create() also call page_pool_destroy() */
> + refcount_set(&pool->user_cnt, 1);
> +
> if (pool->p.flags & PP_FLAG_DMA_MAP)
> get_device(pool->p.dev);
>
> @@ -70,6 +73,7 @@ struct page_pool *page_pool_create(const struct page_pool_params *params)
> kfree(pool);
> return ERR_PTR(err);
> }
> +
> return pool;
> }
> EXPORT_SYMBOL(page_pool_create);
> @@ -356,6 +360,10 @@ static void __warn_in_flight(struct page_pool *pool)
>
> void __page_pool_free(struct page_pool *pool)
> {
> + /* Only last user actually free/release resources */
> + if (!page_pool_put(pool))
> + return;
> +
> WARN(pool->alloc.count, "API usage violation");
> WARN(!ptr_ring_empty(&pool->ring), "ptr_ring is not empty");
>
> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index 829377cc83db..d7bf62ffbb5e 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -370,6 +370,9 @@ int xdp_rxq_info_reg_mem_model(struct xdp_rxq_info *xdp_rxq,
> goto err;
> }
>
> + if (type == MEM_TYPE_PAGE_POOL)
> + page_pool_get(xdp_alloc->page_pool);
> +
> mutex_unlock(&mem_id_lock);
>
> trace_mem_connect(xdp_alloc, xdp_rxq);



--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer

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