net: page_pool: avoid false positive warning if NAPI was never added

We expect NAPI to be in disabled state when page pool is torn down.
But it is also legal if the NAPI is completely uninitialized.

Reviewed-by: Mina Almasry <almasrymina@google.com>
Link: https://patch.msgid.link/20250206225638.1387810-4-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/core/dev.h b/net/core/dev.h
index a5b166bbd169a0aea925dd794db25f26418de87d..caa13e431a6bcfdc4aad1cbcaa4a9487e34e2fa6 100644 (file)
--- a/net/core/dev.h
+++ b/net/core/dev.h
@@ -299,6 +299,18 @@ void xdp_do_check_flushed(struct napi_struct *napi);
 static inline void xdp_do_check_flushed(struct napi_struct *napi) { }
 #endif
 
+/* Best effort check that NAPI is not idle (can't be scheduled to run) */
+static inline void napi_assert_will_not_race(const struct napi_struct *napi)
+{
+       /* uninitialized instance, can't race */
+       if (!napi->poll_list.next)
+               return;
+
+       /* SCHED bit is set on disabled instances */
+       WARN_ON(!test_bit(NAPI_STATE_SCHED, &napi->state));
+       WARN_ON(READ_ONCE(napi->list_owner) != -1);
+}
+
 void kick_defer_list_purge(struct softnet_data *sd, unsigned int cpu);
 
 #define XMIT_RECURSION_LIMIT   8

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 686bd4a117d93d86c71da2fdfffc32fcfd7b9e40..1c6fec08bc43498c443b4278de0f910b793901db 100644 (file)
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -26,6 +26,7 @@
 
 #include <trace/events/page_pool.h>
 
+#include "dev.h"
 #include "mp_dmabuf_devmem.h"
 #include "netmem_priv.h"
 #include "page_pool_priv.h"
@@ -1147,11 +1148,7 @@ void page_pool_disable_direct_recycling(struct page_pool *pool)
        if (!pool->p.napi)
                return;
 
-       /* To avoid races with recycling and additional barriers make sure
-        * pool and NAPI are unlinked when NAPI is disabled.
-        */
-       WARN_ON(!test_bit(NAPI_STATE_SCHED, &pool->p.napi->state));
-       WARN_ON(READ_ONCE(pool->p.napi->list_owner) != -1);
+       napi_assert_will_not_race(pool->p.napi);
 
        mutex_lock(&page_pools_lock);
        WRITE_ONCE(pool->p.napi, NULL);