[RFC net-next 2/6] mm: add a signature in struct page

[Matteo Croce <mcroce@linux.microsoft.com>]

From: Matteo Croce <mcroce@microsoft.com>

This is needed by the page_pool to avoid recycling a page not allocated
via page_pool.

Signed-off-by: Matteo Croce <mcroce@microsoft.com>
---
 include/linux/mm_types.h | 1 +
 include/net/page_pool.h  | 2 ++
 net/core/page_pool.c     | 4 ++++
 3 files changed, 7 insertions(+)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 0974ad501a47..67caade433e4 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -100,6 +100,7 @@ struct page {
 			 * 32-bit architectures.
 			 */
 			dma_addr_t dma_addr;
+			unsigned long signature;
 		};
 		struct {	/* slab, slob and slub */
 			union {
diff --git a/include/net/page_pool.h b/include/net/page_pool.h
index b5b195305346..b30405e84b5e 100644
--- a/include/net/page_pool.h
+++ b/include/net/page_pool.h
@@ -63,6 +63,8 @@
  */
 #define PP_ALLOC_CACHE_SIZE	128
 #define PP_ALLOC_CACHE_REFILL	64
+#define PP_SIGNATURE		0x20210303
+
 struct pp_alloc_cache {
 	u32 count;
 	void *cache[PP_ALLOC_CACHE_SIZE];
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index ad8b0707af04..2ae9b554ef98 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -232,6 +232,8 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
 		page_pool_dma_sync_for_device(pool, page, pool->p.max_len);
 
 skip_dma_map:
+	page->signature = PP_SIGNATURE;
+
 	/* Track how many pages are held 'in-flight' */
 	pool->pages_state_hold_cnt++;
 
@@ -302,6 +304,8 @@ void page_pool_release_page(struct page_pool *pool, struct page *page)
 			     DMA_ATTR_SKIP_CPU_SYNC);
 	page->dma_addr = 0;
 skip_dma_unmap:
+	page->signature = 0;
+
 	/* This may be the last page returned, releasing the pool, so
 	 * it is not safe to reference pool afterwards.
 	 */
-- 
2.29.2