netdev - [PATCH net-next] net: warn if NAPI instance wasn't shut down

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Message-ID: <20250203215816.1294081-1-kuba@kernel.org>
Date: Mon,  3 Feb 2025 13:58:16 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: davem@...emloft.net
Cc: netdev@...r.kernel.org,
	edumazet@...gle.com,
	pabeni@...hat.com,
	andrew+netdev@...n.ch,
	horms@...nel.org,
	Jakub Kicinski <kuba@...nel.org>
Subject: [PATCH net-next] net: warn if NAPI instance wasn't shut down

Drivers should always disable a NAPI instance before removing it.
If they don't the instance may be queued for polling.
Since commit 86e25f40aa1e ("net: napi: Add napi_config")
we also remove the NAPI from the busy polling hash table
in napi_disable(), so not disabling would leave a stale
entry there.

Use of busy polling is relatively uncommon so bugs may be lurking
in the drivers. Add an explicit warning.

Signed-off-by: Jakub Kicinski <kuba@...nel.org>
---
 net/core/dev.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/core/dev.c b/net/core/dev.c
index c0021cbd28fc..2b141f20b13b 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -7071,6 +7071,9 @@ void __netif_napi_del_locked(struct napi_struct *napi)
 	if (!test_and_clear_bit(NAPI_STATE_LISTED, &napi->state))
 		return;
 
+	/* Make sure NAPI is disabled (or was never enabled). */
+	WARN_ON(!test_bit(NAPI_STATE_SCHED, &napi->state));
+
 	if (napi->config) {
 		napi->index = -1;
 		napi->config = NULL;
-- 
2.48.1