[PATCH v4 net-next 1/4] net: core: page_pool: add user cnt preventing pool deletion

[Ivan Khoronzhuk]

Add user counter allowing to delete pool only when no users.
It doesn't prevent pool from flush, only prevents freeing the
pool instance. Helps when no need to delete the pool and now
it's user responsibility to free it by calling page_pool_free()
while destroying procedure. It also makes to use page_pool_free()
explicitly, not fully hidden in xdp unreg, which looks more
correct after page pool "create" routine.

Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@xxxxxxxxxx>
---
 drivers/net/ethernet/mellanox/mlx5/core/en_main.c | 8 +++++---
 include/net/page_pool.h                           | 7 +++++++
 net/core/page_pool.c                              | 7 +++++++
 net/core/xdp.c                                    | 3 +++
 4 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
index 5e40db8f92e6..cb028de64a1d 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 +611,8 @@ 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);
+	if (rq->page_pool)
+		page_pool_free(rq->page_pool);
 	mlx5_wq_destroy(&rq->wq_ctrl);
 
 	return err;
@@ -643,6 +643,8 @@ static void mlx5e_free_rq(struct mlx5e_rq *rq)
 	}
 
 	xdp_rxq_info_unreg(&rq->xdp_rxq);
+	if (rq->page_pool)
+		page_pool_free(rq->page_pool);
 	mlx5_wq_destroy(&rq->wq_ctrl);
 }
 
diff --git a/include/net/page_pool.h b/include/net/page_pool.h
index f07c518ef8a5..1ec838e9927e 100644
--- a/include/net/page_pool.h
+++ b/include/net/page_pool.h
@@ -101,6 +101,7 @@ struct page_pool {
 	struct ptr_ring ring;
 
 	atomic_t pages_state_release_cnt;
+	atomic_t user_cnt;
 };
 
 struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp);
@@ -183,6 +184,12 @@ static inline dma_addr_t page_pool_get_dma_addr(struct page *page)
 	return page->dma_addr;
 }
 
+/* used to prevent pool from deallocation */
+static inline void page_pool_get(struct page_pool *pool)
+{
+	atomic_inc(&pool->user_cnt);
+}
+
 static inline bool is_page_pool_compiled_in(void)
 {
 #ifdef CONFIG_PAGE_POOL
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index b366f59885c1..169b0e3c870e 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -48,6 +48,7 @@ static int page_pool_init(struct page_pool *pool,
 		return -ENOMEM;
 
 	atomic_set(&pool->pages_state_release_cnt, 0);
+	atomic_set(&pool->user_cnt, 0);
 
 	if (pool->p.flags & PP_FLAG_DMA_MAP)
 		get_device(pool->p.dev);
@@ -70,6 +71,8 @@ struct page_pool *page_pool_create(const struct page_pool_params *params)
 		kfree(pool);
 		return ERR_PTR(err);
 	}
+
+	page_pool_get(pool);
 	return pool;
 }
 EXPORT_SYMBOL(page_pool_create);
@@ -356,6 +359,10 @@ static void __warn_in_flight(struct page_pool *pool)
 
 void __page_pool_free(struct page_pool *pool)
 {
+	/* free only if no users */
+	if (!atomic_dec_and_test(&pool->user_cnt))
+		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..04bdcd784d2e 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -372,6 +372,9 @@ int xdp_rxq_info_reg_mem_model(struct xdp_rxq_info *xdp_rxq,
 
 	mutex_unlock(&mem_id_lock);
 
+	if (type == MEM_TYPE_PAGE_POOL)
+		page_pool_get(xdp_alloc->page_pool);
+
 	trace_mem_connect(xdp_alloc, xdp_rxq);
 	return 0;
 err:
-- 
2.17.1