fix race

From: Jesper Dangaard Brouer <brouer@redhat.com>

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
---
 net/core/page_pool.c |   48 ++++++++++++++++++++++++++++++++++--------------
 1 file changed, 34 insertions(+), 14 deletions(-)

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index ce7e8dda6403..25139b162674 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -451,9 +451,8 @@ EXPORT_SYMBOL(page_pool_alloc_pages);
  */
 #define _distance(a, b)	(s32)((a) - (b))
 
-static s32 page_pool_inflight(struct page_pool *pool)
+static s32 __page_pool_inflight(struct page_pool *pool, u32 release_cnt)
 {
-	u32 release_cnt = atomic_read(&pool->pages_state_release_cnt);
 	u32 hold_cnt = READ_ONCE(pool->pages_state_hold_cnt);
 	s32 inflight;
 
@@ -465,6 +464,14 @@ static s32 page_pool_inflight(struct page_pool *pool)
 	return inflight;
 }
 
+static s32 page_pool_inflight(struct page_pool *pool)
+{
+	u32 release_cnt = atomic_read(&pool->pages_state_release_cnt);
+	return __page_pool_inflight(pool, release_cnt);
+}
+
+static int page_pool_free_attempt(struct page_pool *pool, u32 release_cnt);
+
 /* Disconnects a page (from a page_pool).  API users can have a need
  * to disconnect a page (from a page_pool), to allow it to be used as
  * a regular page (that will eventually be returned to the normal
@@ -473,7 +480,7 @@ static s32 page_pool_inflight(struct page_pool *pool)
 void page_pool_release_page(struct page_pool *pool, struct page *page)
 {
 	dma_addr_t dma;
-	int count;
+	u32 count;
 
 	if (!(pool->p.flags & PP_FLAG_DMA_MAP))
 		/* Always account for inflight pages, even if we didn't
@@ -490,8 +497,12 @@ void page_pool_release_page(struct page_pool *pool, struct page *page)
 	page_pool_set_dma_addr(page, 0);
 skip_dma_unmap:
 	page_pool_clear_pp_info(page);
-	count = atomic_inc_return_relaxed(&pool->pages_state_release_cnt);
+	count = atomic_inc_return(&pool->pages_state_release_cnt);
 	trace_page_pool_state_release(pool, page, count);
+
+	/* In shutdown phase, last page will free pool instance */
+	if (pool->p.flags & PP_FLAG_SHUTDOWN)
+		page_pool_free_attempt(pool, count);
 }
 EXPORT_SYMBOL(page_pool_release_page);
 
@@ -543,7 +554,7 @@ static bool page_pool_recycle_in_cache(struct page *page,
 	return true;
 }
 
-static void page_pool_shutdown_attempt(struct page_pool *pool);
+static void page_pool_empty_ring(struct page_pool *pool);
 
 /* If the page refcnt == 1, this will try to recycle the page.
  * if PP_FLAG_DMA_SYNC_DEV is set, we'll try to sync the DMA area for
@@ -610,7 +621,7 @@ void page_pool_put_defragged_page(struct page_pool *pool, struct page *page,
 		page_pool_return_page(pool, page);
 	}
 	if (pool->p.flags & PP_FLAG_SHUTDOWN)
-		page_pool_shutdown_attempt(pool);
+		page_pool_empty_ring(pool);
 }
 EXPORT_SYMBOL(page_pool_put_defragged_page);
 
@@ -660,7 +671,7 @@ void page_pool_put_page_bulk(struct page_pool *pool, void **data,
 
 out:
 	if (pool->p.flags & PP_FLAG_SHUTDOWN)
-		page_pool_shutdown_attempt(pool);
+		page_pool_empty_ring(pool);
 }
 EXPORT_SYMBOL(page_pool_put_page_bulk);
 
@@ -743,6 +754,7 @@ struct page *page_pool_alloc_frag(struct page_pool *pool,
 }
 EXPORT_SYMBOL(page_pool_alloc_frag);
 
+noinline
 static void page_pool_empty_ring(struct page_pool *pool)
 {
 	struct page *page;
@@ -802,22 +814,28 @@ static void page_pool_scrub(struct page_pool *pool)
 	page_pool_empty_ring(pool);
 }
 
-static int page_pool_release(struct page_pool *pool)
+noinline
+static int page_pool_free_attempt(struct page_pool *pool, u32 release_cnt)
 {
 	int inflight;
 
-	page_pool_scrub(pool);
-	inflight = page_pool_inflight(pool);
+	inflight = __page_pool_inflight(pool, release_cnt);
 	if (!inflight)
 		page_pool_free(pool);
 
 	return inflight;
 }
 
-noinline
-static void page_pool_shutdown_attempt(struct page_pool *pool)
+static int page_pool_release(struct page_pool *pool)
 {
-	page_pool_release(pool);
+	int inflight;
+
+	page_pool_scrub(pool);
+	inflight = page_pool_inflight(pool);
+	if (!inflight)
+		page_pool_free(pool);
+
+	return inflight;
 }
 
 void page_pool_use_xdp_mem(struct page_pool *pool, void (*disconnect)(void *),
@@ -861,7 +879,9 @@ void page_pool_destroy(struct page_pool *pool)
 	 * Enter into shutdown phase, and retry release to handle races.
 	 */
 	pool->p.flags |= PP_FLAG_SHUTDOWN;
-	page_pool_shutdown_attempt(pool);
+
+	/* Concurrent CPUs could have returned last pages into ptr_ring */
+	page_pool_empty_ring(pool);
 }
 EXPORT_SYMBOL(page_pool_destroy);