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    Subject[PATCH v8 net-next 1/5] net: core: page_pool: add user refcnt and reintroduce page_pool_destroy
    Date
    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 Khoronzhuk'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>
    Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
    Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
    ---
    .../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);
    --
    2.17.1
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