From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 C9DBA31D367 for ; Sat, 26 Sep 2026 01:36:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790386606; cv=none; b=mHme+STFadv42VrsdHPqXKmP0JZhHc7vaBJtwOYvm3VGQzchpWuujNwcmdsMPwer2MQAKOCa9jNAQku4ikKVqu24GfzAzPZAO4+Jd2D1XXlvnSixgepi4wYuZU39CyR4KhikIB5RhHIrOjk3i+UIMylJaCjSe9EtK2dwGcWx9BM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790386606; c=relaxed/simple; bh=QqKrD9Uq42OS0UXjsdDoaCZBhquCZvUyyM0OtU9osQs=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=YutQ4kH1K2U1sBnSMHIflMRtncBzH/8D5JsSjUwB9wFwIjorF+v9tE1V0H8zGPZ/HUdQ0sSvbQSjrdpn3m4FzBPjIvu8WHacj+tPngqHlX7ibqfxDz0fqAaA2sxyx935/biCGv7J8s3nXUH+bhsQr8Gu8XsnCaTOWs1X7Z1oNCQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LDRM3w3F; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="LDRM3w3F" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 26F2F1F000FF; Sat, 26 Sep 2026 01:36:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790386604; bh=R0s8YzloE72hdBVusREgE7EXBhzeXd7mIoR3aeZn82o=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=LDRM3w3F/Kyv3wYsBCM4qoDZTqyc9T/6OrVC6QIveXhZDdJfSyTw/mfxppssdVCYj vLECfTJGZfDk7MKVU0+iXc6EKa3KR1QVfQrNcVGSnYv+FaBrozvjXLcHo5Cv97bMt2 SILMPubQ33/MUntOmr0BCRsZDVDRnoPsYt5cYXw5g5AXNslcadsdM/tnpUqNgEaPdm DOz5+007x/WAQ6dhkKEY3NxHLpWGRt0FQsHdBsmHAHaCS21QtdGS927qsImAJoP85d HcQzgwt6+niA9Q4Vds4kvfpm6wJZdJXPLOFUvRP9VZXXSHk6T2rrtLbUMfxqxSN5yA YEmcjLdfKf4MA== Date: Fri, 25 Sep 2026 18:36:43 -0700 From: Jakub Kicinski To: edumazet@google.com, sdf.kernel@gmail.com Cc: davem@davemloft.net, netdev@vger.kernel.org, pabeni@redhat.com, andrew+netdev@lunn.ch, horms@kernel.org Subject: Re: [PATCH net-next 1/2] net: use a single lockdep class for the netdev instance lock Message-ID: <20260925183643.4f7d9eb8@kernel.org> In-Reply-To: <20260923223545.3815583-1-kuba@kernel.org> References: <20260923223545.3815583-1-kuba@kernel.org> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Wed, 23 Sep 2026 15:35:44 -0700 Jakub Kicinski wrote: > (dev)->qdisc_tx_busylock = &qdisc_tx_busylock_key; \ > lockdep_set_class(&(dev)->addr_list_lock, \ > &dev_addr_list_lock_key); \ > - lockdep_set_class(&(dev)->lock, \ > - &dev_instance_lock_key); \ > - lock_set_cmp_fn(&dev->lock, netdev_lock_cmp_fn, NULL); \ > for (i = 0; i < (dev)->num_tx_queues; i++) \ > lockdep_set_class(&(dev)->_tx[i]._xmit_lock, \ > &qdisc_xmit_lock_key); \ > diff --git a/net/core/dev.c b/net/core/dev.c > index c67900354fa6..bca7b267f937 100644 > --- a/net/core/dev.c > +++ b/net/core/dev.c > @@ -568,6 +568,22 @@ static inline void netdev_set_addr_lockdep_class(struct net_device *dev) > } > #endif > > +#ifdef CONFIG_PROVE_LOCKING > +static int netdev_lock_cmp_fn(const struct lockdep_map *a, > + const struct lockdep_map *b) > +{ > + if (a == b) > + return 0; > + > + /* Allow locking multiple devices only under rtnl_lock, > + * the exact order doesn't matter. > + * Note that upper devices don't lock their ops, so nesting > + * mostly happens in batched device removal for now. > + */ > + return lockdep_rtnl_is_held() ? -1 : 1; > +} > +#endif ugh, clashiko points out this is weakening the condition more than I thought. Apparently lockdep_rtnl_is_held() is always UNKNOWN (-1) when called from inside lockdep code ;( So this lockdep_rtnl_is_held() is always true, and we would never fire a lockdep warning on instance locks. I need to switch to non-lockdep rtnl_is_held(), I think, and we either bring back the classes for virt devices (but one class for all) or we explicitly handle the virt->phys order that queue leasing needs. Coding it up now, let me see which one is less ugly.