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

From: Jesper Dangaard Brouer <[email-masked]>
Date: Fri, 5 Jul 2019 09:43:46 +0200

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

On Fri,  5 Jul 2019 02:14:02 +0300
Ivan Khoronzhuk <[email-masked]> 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/[email-masked]/
> Fixes: 5c67bf0ec4d0 ("net: netsec: Use page_pool API")
> Signed-off-by: Jesper Dangaard Brouer <[email-masked]>
> Reviewed-by: Ilias Apalodimas <[email-masked]>
> Signed-off-by: Ivan Khoronzhuk <[email-masked]>

Acked-by: Jesper Dangaard Brouer <[email-masked]>

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