Re: [PATCH net] net: page_pool: don't try to stash the napi id

On Mon, 27 Jan 2025 14:31:10 +0100 Toke Høiland-Jørgensen wrote:

quoted

+
+/* page_pool_destroy or page_pool_disable_direct_recycling must be
called before
+ * netif_napi_del if pool->p.napi is set.
+ */

FWIW the comment is better placed on the warning, that's where people
will look when they hit it ;)

quoted

 void page_pool_destroy(struct page_pool *pool);
 void page_pool_use_xdp_mem(struct page_pool *pool, void (*disconnect)(void *),
                           const struct xdp_mem_info *mem);

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 5c4b788b811b..dc82767b2516 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c

@@ -1161,6 +1161,8 @@ void page_pool_destroy(struct page_pool *pool)
        if (!page_pool_put(pool))
                return;

+       DEBUG_NET_WARN_ON(pool->p.napi && !napi_is_valid(pool->p.napi));

IDK what "napi_is_valid()" is. I think like this:

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index a3de752c5178..837ed36472db 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c

@@ -1145,6 +1145,7 @@ void page_pool_disable_direct_recycling(struct page_pool *pool)
         * pool and NAPI are unlinked when NAPI is disabled.
         */
        WARN_ON(!test_bit(NAPI_STATE_SCHED, &pool->p.napi->state));
+       WARN_ON(!test_bit(NAPI_STATE_LISTED, &pool->p.napi->state));
        WARN_ON(READ_ONCE(pool->p.napi->list_owner) != -1);
 
        WRITE_ONCE(pool->p.napi, NULL);

Because page_pool_disable_direct_recycling() must also be called while
NAPI is listed. Technically we should also sync rcu if the driver calls
this directly, because NAPI may be reused :(

quoted

        page_pool_disable_direct_recycling(pool);
        page_pool_free_frag(pool);  

Yeah, good idea; care to send a proper patch? :)

...for net-next ? :)