net/core/page_pool.c - kernel/msm-5.4 - Gitiles

 /* SPDX-License-Identifier: GPL-2.0
  *
  * page_pool.c
  *	Author:	Jesper Dangaard Brouer <netoptimizer@brouer.com>
  *	Copyright (C) 2016 Red Hat, Inc.
  */

 #include <linux/types.h>
 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/device.h>

 #include <net/page_pool.h>
 #include <linux/dma-direction.h>
 #include <linux/dma-mapping.h>
 #include <linux/page-flags.h>
 #include <linux/mm.h> /* for __put_page() */

 #include <trace/events/page_pool.h>

 static int page_pool_init(struct page_pool *pool,
 			  const struct page_pool_params *params)
 {
 	unsigned int ring_qsize = 1024; /* Default */

 	memcpy(&pool->p, params, sizeof(pool->p));

 	/* Validate only known flags were used */
 	if (pool->p.flags & ~(PP_FLAG_ALL))
 		return -EINVAL;

 	if (pool->p.pool_size)
 		ring_qsize = pool->p.pool_size;

 	/* Sanity limit mem that can be pinned down */
 	if (ring_qsize > 32768)
 		return -E2BIG;

 	/* DMA direction is either DMA_FROM_DEVICE or DMA_BIDIRECTIONAL.
 	 * DMA_BIDIRECTIONAL is for allowing page used for DMA sending,
 	 * which is the XDP_TX use-case.
 	 */
 	if ((pool->p.dma_dir != DMA_FROM_DEVICE) &&
 	    (pool->p.dma_dir != DMA_BIDIRECTIONAL))
 		return -EINVAL;

 	if (ptr_ring_init(&pool->ring, ring_qsize, GFP_KERNEL) < 0)
 		return -ENOMEM;

 	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);

 	return 0;
 }

 struct page_pool *page_pool_create(const struct page_pool_params *params)
 {
 	struct page_pool *pool;
 	int err = 0;

 	pool = kzalloc_node(sizeof(*pool), GFP_KERNEL, params->nid);
 	if (!pool)
 		return ERR_PTR(-ENOMEM);

 	err = page_pool_init(pool, params);
 	if (err < 0) {
 		pr_warn("%s() gave up with errno %d\n", __func__, err);
 		kfree(pool);
 		return ERR_PTR(err);
 	}

 	return pool;
 }
 EXPORT_SYMBOL(page_pool_create);

 /* fast path */
 static struct page *__page_pool_get_cached(struct page_pool *pool)
 {
 	struct ptr_ring *r = &pool->ring;
 	struct page *page;

 	/* Quicker fallback, avoid locks when ring is empty */
 	if (__ptr_ring_empty(r))
 		return NULL;

 	/* Test for safe-context, caller should provide this guarantee */
 	if (likely(in_serving_softirq())) {
 		if (likely(pool->alloc.count)) {
 			/* Fast-path */
 			page = pool->alloc.cache[--pool->alloc.count];
 			return page;
 		}
 		/* Slower-path: Alloc array empty, time to refill
 		 *
 		 * Open-coded bulk ptr_ring consumer.
 		 *
 		 * Discussion: the ring consumer lock is not really
 		 * needed due to the softirq/NAPI protection, but
 		 * later need the ability to reclaim pages on the
 		 * ring. Thus, keeping the locks.
 		 */
 		spin_lock(&r->consumer_lock);
 		while ((page = __ptr_ring_consume(r))) {
 			if (pool->alloc.count == PP_ALLOC_CACHE_REFILL)
 				break;
 			pool->alloc.cache[pool->alloc.count++] = page;
 		}
 		spin_unlock(&r->consumer_lock);
 		return page;
 	}

 	/* Slow-path: Get page from locked ring queue */
 	page = ptr_ring_consume(&pool->ring);
 	return page;
 }

 /* slow path */
 noinline
 static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
 						 gfp_t _gfp)
 {
 	struct page *page;
 	gfp_t gfp = _gfp;
 	dma_addr_t dma;

 	/* We could always set __GFP_COMP, and avoid this branch, as
 	 * prep_new_page() can handle order-0 with __GFP_COMP.
 	 */
 	if (pool->p.order)
 		gfp |= __GFP_COMP;

 	/* FUTURE development:
 	 *
 	 * Current slow-path essentially falls back to single page
 	 * allocations, which doesn't improve performance.  This code
 	 * need bulk allocation support from the page allocator code.
 	 */

 	/* Cache was empty, do real allocation */
 	page = alloc_pages_node(pool->p.nid, gfp, pool->p.order);
 	if (!page)
 		return NULL;

 	if (!(pool->p.flags & PP_FLAG_DMA_MAP))
 		goto skip_dma_map;

 	/* Setup DMA mapping: use 'struct page' area for storing DMA-addr
 	 * since dma_addr_t can be either 32 or 64 bits and does not always fit
 	 * into page private data (i.e 32bit cpu with 64bit DMA caps)
 	 * This mapping is kept for lifetime of page, until leaving pool.
 	 */
 	dma = dma_map_page_attrs(pool->p.dev, page, 0,
 				 (PAGE_SIZE << pool->p.order),
 				 pool->p.dma_dir, DMA_ATTR_SKIP_CPU_SYNC);
 	if (dma_mapping_error(pool->p.dev, dma)) {
 		put_page(page);
 		return NULL;
 	}
 	page->dma_addr = dma;

 skip_dma_map:
 	/* Track how many pages are held 'in-flight' */
 	pool->pages_state_hold_cnt++;

 	trace_page_pool_state_hold(pool, page, pool->pages_state_hold_cnt);

 	/* When page just alloc'ed is should/must have refcnt 1. */
 	return page;
 }

 /* For using page_pool replace: alloc_pages() API calls, but provide
  * synchronization guarantee for allocation side.
  */
 struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp)
 {
 	struct page *page;

 	/* Fast-path: Get a page from cache */
 	page = __page_pool_get_cached(pool);
 	if (page)
 		return page;

 	/* Slow-path: cache empty, do real allocation */
 	page = __page_pool_alloc_pages_slow(pool, gfp);
 	return page;
 }
 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);

 	trace_page_pool_inflight(pool, distance, hold_cnt, release_cnt);
 	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)
 {
 	dma_addr_t dma;

 	if (!(pool->p.flags & PP_FLAG_DMA_MAP))
 		goto skip_dma_unmap;

 	dma = page->dma_addr;
 	/* DMA unmap */
 	dma_unmap_page_attrs(pool->p.dev, dma,
 			     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);
 	trace_page_pool_state_release(pool, page,
 			      atomic_read(&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);

 /* Return a page to the page allocator, cleaning up our state */
 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
 	 * __page_cache_release() call).
 	 */
 }

 static bool __page_pool_recycle_into_ring(struct page_pool *pool,
 				   struct page *page)
 {
 	int ret;
 	/* BH protection not needed if current is serving softirq */
 	if (in_serving_softirq())
 		ret = ptr_ring_produce(&pool->ring, page);
 	else
 		ret = ptr_ring_produce_bh(&pool->ring, page);

 	return (ret == 0) ? true : false;
 }

 /* Only allow direct recycling in special circumstances, into the
  * alloc side cache.  E.g. during RX-NAPI processing for XDP_DROP use-case.
  *
  * Caller must provide appropriate safe context.
  */
 static bool __page_pool_recycle_direct(struct page *page,
 				       struct page_pool *pool)
 {
 	if (unlikely(pool->alloc.count == PP_ALLOC_CACHE_SIZE))
 		return false;

 	/* Caller MUST have verified/know (page_ref_count(page) == 1) */
 	pool->alloc.cache[pool->alloc.count++] = page;
 	return true;
 }

 void __page_pool_put_page(struct page_pool *pool,
 			  struct page *page, bool allow_direct)
 {
 	/* This allocator is optimized for the XDP mode that uses
 	 * one-frame-per-page, but have fallbacks that act like the
 	 * regular page allocator APIs.
 	 *
 	 * refcnt == 1 means page_pool owns page, and can recycle it.
 	 */
 	if (likely(page_ref_count(page) == 1)) {
 		/* Read barrier done in page_ref_count / READ_ONCE */

 		if (allow_direct && in_serving_softirq())
 			if (__page_pool_recycle_direct(page, pool))
 				return;

 		if (!__page_pool_recycle_into_ring(pool, page)) {
 			/* Cache full, fallback to free pages */
 			__page_pool_return_page(pool, page);
 		}
 		return;
 	}
 	/* Fallback/non-XDP mode: API user have elevated refcnt.
 	 *
 	 * Many drivers split up the page into fragments, and some
 	 * want to keep doing this to save memory and do refcnt based
 	 * recycling. Support this use case too, to ease drivers
 	 * switching between XDP/non-XDP.
 	 *
 	 * In-case page_pool maintains the DMA mapping, API user must
 	 * call page_pool_put_page once.  In this elevated refcnt
 	 * case, the DMA is unmapped/released, as driver is likely
 	 * doing refcnt based recycle tricks, meaning another process
 	 * will be invoking put_page.
 	 */
 	__page_pool_clean_page(pool, page);
 	put_page(page);
 }
 EXPORT_SYMBOL(__page_pool_put_page);

 static void __page_pool_empty_ring(struct page_pool *pool)
 {
 	struct page *page;

 	/* Empty recycle ring */
 	while ((page = ptr_ring_consume_bh(&pool->ring))) {
 		/* Verify the refcnt invariant of cached pages */
 		if (!(page_ref_count(page) == 1))
 			pr_crit("%s() page_pool refcnt %d violation\n",
 				__func__, page_ref_count(page));

 		__page_pool_return_page(pool, page);
 	}
 }

 static void __warn_in_flight(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);

 	/* Drivers should fix this, but only problematic when DMA is used */
 	WARN(1, "Still in-flight pages:%d hold:%u released:%u",
 	     distance, hold_cnt, release_cnt);
 }

 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");

 	/* Can happen due to forced shutdown */
 	if (!__page_pool_safe_to_destroy(pool))
 		__warn_in_flight(pool);

 	ptr_ring_cleanup(&pool->ring, NULL);

 	if (pool->p.flags & PP_FLAG_DMA_MAP)
 		put_device(pool->p.dev);

 	kfree(pool);
 }
 EXPORT_SYMBOL(__page_pool_free);

 /* 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;

 	/* Empty alloc cache, assume caller made sure this is
 	 * no-longer in use, and page_pool_alloc_pages() cannot be
 	 * call concurrently.
 	 */
 	while (pool->alloc.count) {
 		page = pool->alloc.cache[--pool->alloc.count];
 		__page_pool_return_page(pool, page);
 	}

 	/* No more consumers should exist, but producers could still
 	 * be in-flight.
 	 */
 	__page_pool_empty_ring(pool);

 	return __page_pool_safe_to_destroy(pool);
 }
 EXPORT_SYMBOL(__page_pool_request_shutdown);
	/* SPDX-License-Identifier: GPL-2.0
	*
	* page_pool.c
	* Author: Jesper Dangaard Brouer <netoptimizer@brouer.com>
	* Copyright (C) 2016 Red Hat, Inc.
	*/

	#include <linux/types.h>
	#include <linux/kernel.h>
	#include <linux/slab.h>
	#include <linux/device.h>

	#include <net/page_pool.h>
	#include <linux/dma-direction.h>
	#include <linux/dma-mapping.h>
	#include <linux/page-flags.h>
	#include <linux/mm.h> /* for __put_page() */

	#include <trace/events/page_pool.h>

	static int page_pool_init(struct page_pool *pool,
	const struct page_pool_params *params)
	{
	unsigned int ring_qsize = 1024; /* Default */

	memcpy(&pool->p, params, sizeof(pool->p));

	/* Validate only known flags were used */
	if (pool->p.flags & ~(PP_FLAG_ALL))
	return -EINVAL;

	if (pool->p.pool_size)
	ring_qsize = pool->p.pool_size;

	/* Sanity limit mem that can be pinned down */
	if (ring_qsize > 32768)
	return -E2BIG;

	/* DMA direction is either DMA_FROM_DEVICE or DMA_BIDIRECTIONAL.
	* DMA_BIDIRECTIONAL is for allowing page used for DMA sending,
	* which is the XDP_TX use-case.
	*/
	if ((pool->p.dma_dir != DMA_FROM_DEVICE) &&
	(pool->p.dma_dir != DMA_BIDIRECTIONAL))
	return -EINVAL;

	if (ptr_ring_init(&pool->ring, ring_qsize, GFP_KERNEL) < 0)
	return -ENOMEM;

	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);

	return 0;
	}

	struct page_pool page_pool_create(const struct page_pool_params params)
	{
	struct page_pool *pool;
	int err = 0;

	pool = kzalloc_node(sizeof(*pool), GFP_KERNEL, params->nid);
	if (!pool)
	return ERR_PTR(-ENOMEM);

	err = page_pool_init(pool, params);
	if (err < 0) {
	pr_warn("%s() gave up with errno %d\n", __func__, err);
	kfree(pool);
	return ERR_PTR(err);
	}

	return pool;
	}
	EXPORT_SYMBOL(page_pool_create);

	/* fast path */
	static struct page __page_pool_get_cached(struct page_pool pool)
	{
	struct ptr_ring *r = &pool->ring;
	struct page *page;

	/* Quicker fallback, avoid locks when ring is empty */
	if (__ptr_ring_empty(r))
	return NULL;

	/* Test for safe-context, caller should provide this guarantee */
	if (likely(in_serving_softirq())) {
	if (likely(pool->alloc.count)) {
	/* Fast-path */
	page = pool->alloc.cache[--pool->alloc.count];
	return page;
	}
	/* Slower-path: Alloc array empty, time to refill
	*
	* Open-coded bulk ptr_ring consumer.
	*
	* Discussion: the ring consumer lock is not really
	* needed due to the softirq/NAPI protection, but
	* later need the ability to reclaim pages on the
	* ring. Thus, keeping the locks.
	*/
	spin_lock(&r->consumer_lock);
	while ((page = __ptr_ring_consume(r))) {
	if (pool->alloc.count == PP_ALLOC_CACHE_REFILL)
	break;
	pool->alloc.cache[pool->alloc.count++] = page;
	}
	spin_unlock(&r->consumer_lock);
	return page;
	}

	/* Slow-path: Get page from locked ring queue */
	page = ptr_ring_consume(&pool->ring);
	return page;
	}

	/* slow path */
	noinline
	static struct page __page_pool_alloc_pages_slow(struct page_pool pool,
	gfp_t _gfp)
	{
	struct page *page;
	gfp_t gfp = _gfp;
	dma_addr_t dma;

	/* We could always set __GFP_COMP, and avoid this branch, as
	* prep_new_page() can handle order-0 with __GFP_COMP.
	*/
	if (pool->p.order)
	gfp \|= __GFP_COMP;

	/* FUTURE development:
	*
	* Current slow-path essentially falls back to single page
	* allocations, which doesn't improve performance. This code
	* need bulk allocation support from the page allocator code.
	*/

	/* Cache was empty, do real allocation */
	page = alloc_pages_node(pool->p.nid, gfp, pool->p.order);
	if (!page)
	return NULL;

	if (!(pool->p.flags & PP_FLAG_DMA_MAP))
	goto skip_dma_map;

	/* Setup DMA mapping: use 'struct page' area for storing DMA-addr
	* since dma_addr_t can be either 32 or 64 bits and does not always fit
	* into page private data (i.e 32bit cpu with 64bit DMA caps)
	* This mapping is kept for lifetime of page, until leaving pool.
	*/
	dma = dma_map_page_attrs(pool->p.dev, page, 0,
	(PAGE_SIZE << pool->p.order),
	pool->p.dma_dir, DMA_ATTR_SKIP_CPU_SYNC);
	if (dma_mapping_error(pool->p.dev, dma)) {
	put_page(page);
	return NULL;
	}
	page->dma_addr = dma;

	skip_dma_map:
	/* Track how many pages are held 'in-flight' */
	pool->pages_state_hold_cnt++;

	trace_page_pool_state_hold(pool, page, pool->pages_state_hold_cnt);

	/* When page just alloc'ed is should/must have refcnt 1. */
	return page;
	}

	/* For using page_pool replace: alloc_pages() API calls, but provide
	* synchronization guarantee for allocation side.
	*/
	struct page page_pool_alloc_pages(struct page_pool pool, gfp_t gfp)
	{
	struct page *page;

	/* Fast-path: Get a page from cache */
	page = __page_pool_get_cached(pool);
	if (page)
	return page;

	/* Slow-path: cache empty, do real allocation */
	page = __page_pool_alloc_pages_slow(pool, gfp);
	return page;
	}
	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);

	trace_page_pool_inflight(pool, distance, hold_cnt, release_cnt);
	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)
	{
	dma_addr_t dma;

	if (!(pool->p.flags & PP_FLAG_DMA_MAP))
	goto skip_dma_unmap;

	dma = page->dma_addr;
	/* DMA unmap */
	dma_unmap_page_attrs(pool->p.dev, dma,
	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);
	trace_page_pool_state_release(pool, page,
	atomic_read(&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);

	/* Return a page to the page allocator, cleaning up our state */
	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
	* __page_cache_release() call).
	*/
	}

	static bool __page_pool_recycle_into_ring(struct page_pool *pool,
	struct page *page)
	{
	int ret;
	/* BH protection not needed if current is serving softirq */
	if (in_serving_softirq())
	ret = ptr_ring_produce(&pool->ring, page);
	else
	ret = ptr_ring_produce_bh(&pool->ring, page);

	return (ret == 0) ? true : false;
	}

	/* Only allow direct recycling in special circumstances, into the
	* alloc side cache. E.g. during RX-NAPI processing for XDP_DROP use-case.
	*
	* Caller must provide appropriate safe context.
	*/
	static bool __page_pool_recycle_direct(struct page *page,
	struct page_pool *pool)
	{
	if (unlikely(pool->alloc.count == PP_ALLOC_CACHE_SIZE))
	return false;

	/* Caller MUST have verified/know (page_ref_count(page) == 1) */
	pool->alloc.cache[pool->alloc.count++] = page;
	return true;
	}

	void __page_pool_put_page(struct page_pool *pool,
	struct page *page, bool allow_direct)
	{
	/* This allocator is optimized for the XDP mode that uses
	* one-frame-per-page, but have fallbacks that act like the
	* regular page allocator APIs.
	*
	* refcnt == 1 means page_pool owns page, and can recycle it.
	*/
	if (likely(page_ref_count(page) == 1)) {
	/* Read barrier done in page_ref_count / READ_ONCE */

	if (allow_direct && in_serving_softirq())
	if (__page_pool_recycle_direct(page, pool))
	return;

	if (!__page_pool_recycle_into_ring(pool, page)) {
	/* Cache full, fallback to free pages */
	__page_pool_return_page(pool, page);
	}
	return;
	}
	/* Fallback/non-XDP mode: API user have elevated refcnt.
	*
	* Many drivers split up the page into fragments, and some
	* want to keep doing this to save memory and do refcnt based
	* recycling. Support this use case too, to ease drivers
	* switching between XDP/non-XDP.
	*
	* In-case page_pool maintains the DMA mapping, API user must
	* call page_pool_put_page once. In this elevated refcnt
	* case, the DMA is unmapped/released, as driver is likely
	* doing refcnt based recycle tricks, meaning another process
	* will be invoking put_page.
	*/
	__page_pool_clean_page(pool, page);
	put_page(page);
	}
	EXPORT_SYMBOL(__page_pool_put_page);

	static void __page_pool_empty_ring(struct page_pool *pool)
	{
	struct page *page;

	/* Empty recycle ring */
	while ((page = ptr_ring_consume_bh(&pool->ring))) {
	/* Verify the refcnt invariant of cached pages */
	if (!(page_ref_count(page) == 1))
	pr_crit("%s() page_pool refcnt %d violation\n",
	__func__, page_ref_count(page));

	__page_pool_return_page(pool, page);
	}
	}

	static void __warn_in_flight(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);

	/* Drivers should fix this, but only problematic when DMA is used */
	WARN(1, "Still in-flight pages:%d hold:%u released:%u",
	distance, hold_cnt, release_cnt);
	}

	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");

	/* Can happen due to forced shutdown */
	if (!__page_pool_safe_to_destroy(pool))
	__warn_in_flight(pool);

	ptr_ring_cleanup(&pool->ring, NULL);

	if (pool->p.flags & PP_FLAG_DMA_MAP)
	put_device(pool->p.dev);

	kfree(pool);
	}
	EXPORT_SYMBOL(__page_pool_free);

	/* 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;

	/* Empty alloc cache, assume caller made sure this is
	* no-longer in use, and page_pool_alloc_pages() cannot be
	* call concurrently.
	*/
	while (pool->alloc.count) {
	page = pool->alloc.cache[--pool->alloc.count];
	__page_pool_return_page(pool, page);
	}

	/* No more consumers should exist, but producers could still
	* be in-flight.
	*/
	__page_pool_empty_ring(pool);

	return __page_pool_safe_to_destroy(pool);
	}
	EXPORT_SYMBOL(__page_pool_request_shutdown);