Subject: Re: [PATCH net-next V2] net: core: page_pool: add user refcnt and reintroduce page_pool_destroy

From: Ilias Apalodimas <[email-masked]>
Date: Thu, 4 Jul 2019 20:22:44 +0300

Hi Jesper,

> 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 use-case is
> explicitly denied in this V2 patch, as it needs more discussion upstream.
> 
> 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]>
> ---
> 
> I hope we can agree on this first step. Afterwards we can discuss, which is the
> best approach for Ivan's two netdev's with one RX-queue API change.
> 
>  drivers/net/ethernet/mellanox/mlx5/core/en_main.c |    6 ++---
>  drivers/net/ethernet/socionext/netsec.c           |    8 ++----
>  include/net/page_pool.h                           |   26 +++++++++++++++++++++
>  net/core/page_pool.c                              |    8 ++++++
>  net/core/xdp.c                                    |    9 +++++++
>  5 files changed, 48 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> index 1085040675ae..ce1c7a449eae 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> @@ -545,10 +545,8 @@ 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;
> -	}
>  
>  	for (i = 0; i < wq_sz; i++) {
>  		if (rq->wq_type == MLX5_WQ_TYPE_LINKED_LIST_STRIDING_RQ) {
> @@ -613,6 +611,7 @@ 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;
> @@ -643,6 +642,7 @@ 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..0a0984d8f5d5 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 +216,15 @@ static inline bool is_page_pool_compiled_in(void)
>  #endif
>  }
>  
> +static inline unsigned int page_pool_get(struct page_pool *pool)
> +{
> +	refcount_inc(&pool->user_cnt);
> +	return refcount_read(&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 b29d7b513a18..57c2317d9ce5 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -370,6 +370,15 @@ int xdp_rxq_info_reg_mem_model(struct xdp_rxq_info *xdp_rxq,
>  		goto err;
>  	}
>  
> +	if (type == MEM_TYPE_PAGE_POOL) {
> +		if (page_pool_get(xdp_alloc->page_pool) > 2) {
> +			WARN(1, "API misuse, argue to enable use-case");
> +			page_pool_put(xdp_alloc->page_pool);
> +			errno = -EINVAL;
> +			goto err;
> +		}
> +	}
> +
>  	mutex_unlock(&mem_id_lock);
>  
>  	trace_mem_connect(xdp_alloc, xdp_rxq);
> 
For the netsec and page_pool part 

Reviewed-by: Ilias Apalodimas <[email-masked]>