From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3B9B817A300; Fri, 8 Aug 2025 01:50:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754617808; cv=none; b=iCA8511x7zmD7sAPedDQbdlbKKqW4WiLQh6MwJ3prtzF30QLRrb2B8LBQEyOD511D3Yz+LAaEdsV+beRMdzFqiMHqDOtecxiy2YlTi0p4QwDbxG3wBfUdOhSeam2daHGMv0wqWyys41sXemdUPzBmko1DaVFRzTgDK6smx1Lne8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754617808; c=relaxed/simple; bh=/byPVV+VMNKmftJfebXwe65jG0gcjrDuEVrZbGQmN7M=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=IgvsJeAR/J+lC1roDqxBvl2NsxOcRL0e696iQgyoF+mhiHwPMPZSm8P4g0KWCfsQJBZA4gSn22e34a2qbLM76WfhMfMBQHD9DrH45dPNvSEA+Hk1IxckCnxgiDDxN/rg/fl3ebDFgGZzldBch043smkZ8J5XVFFWAft35wqRUms= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=pEWN04P5; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="pEWN04P5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B1B12C4CEEB; Fri, 8 Aug 2025 01:50:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1754617808; bh=/byPVV+VMNKmftJfebXwe65jG0gcjrDuEVrZbGQmN7M=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=pEWN04P5/VRVi8RPH3nkMgeRVfYUIwp58MJBOvtppo0/iesA8atOib7phv/nd7Icb bvvxX/anER1Ixt5RJEH+ePQirjh87N1Qz5b/2RUu1gIgAgJCY+f91TdSKOsLZJNguN VPIlrqorO8IuYW6ZPGnhB+RbF/28iHU1vKzfg/hU8MvqRVaP6D1k1z3H8FO2IySs91 p+I1OBKRemSxe8fPU4PZSLrzypsKIWDKAOJL9sYEVxslqIpLF78W5OrbNCxf3W5PFB XvVL7r/BU9/6LImyRYVqZhJkBATRVCMeFNUFjCudQv3xj8rLy/cUoVxTcSmUwB45bp WpJ7i7WeUNrjQ== From: Jakub Kicinski To: davem@davemloft.net Cc: netdev@vger.kernel.org, edumazet@google.com, pabeni@redhat.com, andrew+netdev@lunn.ch, horms@kernel.org, willemdebruijn.kernel@gmail.com, skhawaja@google.com, joe@dama.to, sdf@fomichev.me, shuah@kernel.org, linux-kselftest@vger.kernel.org, Jakub Kicinski Subject: [PATCH net 3/3] net: prevent deadlocks when enabling NAPIs with mixed kthread config Date: Thu, 7 Aug 2025 18:49:52 -0700 Message-ID: <20250808014952.724762-4-kuba@kernel.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20250808014952.724762-1-kuba@kernel.org> References: <20250808014952.724762-1-kuba@kernel.org> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The following order of calls currently deadlocks if: - device has threaded=1; and - NAPI has persistent config with threaded=0. netif_napi_add_weight_config() dev->threaded == 1 napi_kthread_create() napi_enable() napi_restore_config() napi_set_threaded(0) napi_stop_kthread() while (NAPIF_STATE_SCHED) msleep(20) We deadlock because disabled NAPI has STATE_SCHED set. Creating a thread in netif_napi_add() just to destroy it in napi_disable() is fairly ugly in the first place. Let's read both the device config and the NAPI config in netif_napi_add(). Fixes: e6d76268813d ("net: Update threaded state in napi config in netif_set_threaded") Signed-off-by: Jakub Kicinski --- net/core/dev.h | 8 ++++++++ net/core/dev.c | 5 +++-- 2 files changed, 11 insertions(+), 2 deletions(-) diff --git a/net/core/dev.h b/net/core/dev.h index ab69edc0c3e3..d6b08d435479 100644 --- a/net/core/dev.h +++ b/net/core/dev.h @@ -323,6 +323,14 @@ static inline enum netdev_napi_threaded napi_get_threaded(struct napi_struct *n) return NETDEV_NAPI_THREADED_DISABLED; } +static inline enum netdev_napi_threaded +napi_get_threaded_config(struct net_device *dev, struct napi_struct *n) +{ + if (n->config) + return n->config->threaded; + return dev->threaded; +} + int napi_set_threaded(struct napi_struct *n, enum netdev_napi_threaded threaded); diff --git a/net/core/dev.c b/net/core/dev.c index f180746382a1..5a3c0f40a93f 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -7357,8 +7357,9 @@ void netif_napi_add_weight_locked(struct net_device *dev, * Clear dev->threaded if kthread creation failed so that * threaded mode will not be enabled in napi_enable(). */ - if (dev->threaded && napi_kthread_create(napi)) - dev->threaded = NETDEV_NAPI_THREADED_DISABLED; + if (napi_get_threaded_config(dev, napi)) + if (napi_kthread_create(napi)) + dev->threaded = NETDEV_NAPI_THREADED_DISABLED; netif_napi_set_irq_locked(napi, -1); } EXPORT_SYMBOL(netif_napi_add_weight_locked); -- 2.50.1