linux-kernel - [PATCH AUTOSEL 6.14 534/642] net: page_pool: avoid false positive warning if NAPI was never added

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Message-Id: <20250505221419.2672473-534-sashal@kernel.org>
Date: Mon,  5 May 2025 18:12:30 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Jakub Kicinski <kuba@...nel.org>,
	Mina Almasry <almasrymina@...gle.com>,
	Sasha Levin <sashal@...nel.org>,
	davem@...emloft.net,
	edumazet@...gle.com,
	pabeni@...hat.com,
	hawk@...nel.org,
	ilias.apalodimas@...aro.org,
	jdamato@...tly.com,
	sdf@...ichev.me,
	kuniyu@...zon.com,
	kory.maincent@...tlin.com,
	mkarsten@...terloo.ca,
	bigeasy@...utronix.de,
	netdev@...r.kernel.org
Subject: [PATCH AUTOSEL 6.14 534/642] net: page_pool: avoid false positive warning if NAPI was never added

From: Jakub Kicinski <kuba@...nel.org>

[ Upstream commit c1e00bc4be06cacee6307cedb9b55bbaddb5044d ]

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@...gle.com>
Link: https://patch.msgid.link/20250206225638.1387810-4-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 net/core/dev.h       | 12 ++++++++++++
 net/core/page_pool.c |  7 ++-----
 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/net/core/dev.h b/net/core/dev.h
index a5b166bbd169a..caa13e431a6bc 100644
--- 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 ede82c610936e..cca51aa2e876f 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -25,6 +25,7 @@
 
 #include <trace/events/page_pool.h>
 
+#include "dev.h"
 #include "mp_dmabuf_devmem.h"
 #include "netmem_priv.h"
 #include "page_pool_priv.h"
@@ -1146,11 +1147,7 @@ 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);
-- 
2.39.5