1 files changed, 46 insertions, 16 deletions

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 41391b5dc14c..8679e24fd665 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -43,6 +43,8 @@ static int page_pool_init(struct page_pool *pool,
 	if (ptr_ring_init(&pool->ring, ring_qsize, GFP_KERNEL) < 0)
 		return -ENOMEM;
 
+	atomic_set(&pool->pages_state_release_cnt, 0);
+
 	return 0;
 }
 
@@ -151,6 +153,9 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
 	page->dma_addr = dma;
 
 skip_dma_map:
+	/* Track how many pages are held 'in-flight' */
+	pool->pages_state_hold_cnt++;
+
 	/* When page just alloc'ed is should/must have refcnt 1. */
 	return page;
 }
@@ -173,6 +178,33 @@ struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp)
 }
 EXPORT_SYMBOL(page_pool_alloc_pages);
 
+/* Calculate distance between two u32 values, valid if distance is below 2^(31)
+ *  https://en.wikipedia.org/wiki/Serial_number_arithmetic#General_Solution
+ */
+#define _distance(a, b)	(s32)((a) - (b))
+
+static s32 page_pool_inflight(struct page_pool *pool)
+{
+	u32 release_cnt = atomic_read(&pool->pages_state_release_cnt);
+	u32 hold_cnt = READ_ONCE(pool->pages_state_hold_cnt);
+	s32 distance;
+
+	distance = _distance(hold_cnt, release_cnt);
+
+	/* TODO: Add tracepoint here */
+	return distance;
+}
+
+static bool __page_pool_safe_to_destroy(struct page_pool *pool)
+{
+	s32 inflight = page_pool_inflight(pool);
+
+	/* The distance should not be able to become negative */
+	WARN(inflight < 0, "Negative(%d) inflight packet-pages", inflight);
+
+	return (inflight == 0);
+}
+
 /* Cleanup page_pool state from page */
 static void __page_pool_clean_page(struct page_pool *pool,
 				   struct page *page)
@@ -180,7 +212,7 @@ static void __page_pool_clean_page(struct page_pool *pool,
 	dma_addr_t dma;
 
 	if (!(pool->p.flags & PP_FLAG_DMA_MAP))
-		return;
+		goto skip_dma_unmap;
 
 	dma = page->dma_addr;
 	/* DMA unmap */
@@ -188,11 +220,16 @@ static void __page_pool_clean_page(struct page_pool *pool,
 			     PAGE_SIZE << pool->p.order, pool->p.dma_dir,
 			     DMA_ATTR_SKIP_CPU_SYNC);
 	page->dma_addr = 0;
+skip_dma_unmap:
+	atomic_inc(&pool->pages_state_release_cnt);
 }
 
 /* unmap the page and clean our state */
 void page_pool_unmap_page(struct page_pool *pool, struct page *page)
 {
+	/* When page is unmapped, this implies page will not be
+	 * returned to page_pool.
+	 */
 	__page_pool_clean_page(pool, page);
 }
 EXPORT_SYMBOL(page_pool_unmap_page);
@@ -201,6 +238,7 @@ EXPORT_SYMBOL(page_pool_unmap_page);
 static void __page_pool_return_page(struct page_pool *pool, struct page *page)
 {
 	__page_pool_clean_page(pool, page);
+
 	put_page(page);
 	/* An optimization would be to call __free_pages(page, pool->p.order)
 	 * knowing page is not part of page-cache (thus avoiding a
@@ -296,24 +334,17 @@ void __page_pool_free(struct page_pool *pool)
 {
 	WARN(pool->alloc.count, "API usage violation");
 	WARN(!ptr_ring_empty(&pool->ring), "ptr_ring is not empty");
+	WARN(!__page_pool_safe_to_destroy(pool), "still in-flight pages");
 
 	ptr_ring_cleanup(&pool->ring, NULL);
 	kfree(pool);
 }
 EXPORT_SYMBOL(__page_pool_free);
 
-static void __page_pool_destroy_rcu(struct rcu_head *rcu)
-{
-	struct page_pool *pool;
-
-	pool = container_of(rcu, struct page_pool, rcu);
-
-	__page_pool_empty_ring(pool);
-	__page_pool_free(pool);
-}
-
-/* Cleanup and release resources */
-void page_pool_destroy(struct page_pool *pool)
+/* Request to shutdown: release pages cached by page_pool, and check
+ * for in-flight pages
+ */
+bool __page_pool_request_shutdown(struct page_pool *pool)
 {
 	struct page *page;
 
@@ -331,7 +362,6 @@ void page_pool_destroy(struct page_pool *pool)
 	 */
 	__page_pool_empty_ring(pool);
 
-	/* An xdp_mem_allocator can still ref page_pool pointer */
-	call_rcu(&pool->rcu, __page_pool_destroy_rcu);
+	return __page_pool_safe_to_destroy(pool);
 }
-EXPORT_SYMBOL(page_pool_destroy);
+EXPORT_SYMBOL(__page_pool_request_shutdown);