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 D0E656CDA8 for ; Wed, 17 Apr 2024 08:35:54 +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=1713342954; cv=none; b=tHFfdzUwxI0NNGiUFDtsMatcmLra9oZnkWxdMeFTZF6GcsyvTTuhDPsUY8V7IRC0FSWrN4uUkLMoz5osfqAOgqL/t4+vDQw38Rr6GiCPbTBVh+dgpCdeT+mEiqu9SOxDhVtexcsAISv+jCIKMf2L6aDniDck+hJ7er4k2KThOXk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713342954; c=relaxed/simple; bh=s7MqT9pXd0kbuCaAXMjSvbDzjWO7b17I9zlKSyXm9g0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ft+lsNvfwATCKnVjT03Lz1kUFUDyTtENgazACz1AnqOyISE0wm27DTrWg7D9gXZJTVUvB18nsvO1IHgMgDA9ShZa8IIKg2fVWYmshRMLffFqkNg0hhF+NlnOHSTRF3PtrMawpP9R3Mg93SZjBPKk92NgNC2YQdRDURfKoVxd5nw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=V7ofZ3Vm; 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="V7ofZ3Vm" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E1433C072AA; Wed, 17 Apr 2024 08:35:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1713342954; bh=s7MqT9pXd0kbuCaAXMjSvbDzjWO7b17I9zlKSyXm9g0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=V7ofZ3VmpRkf9j6JEdc9KaRYvc4+wsR2C0/EgSm8QOjKIx33XcRMMQwnenp7xuMdX xW0r1jYTESj/iFEBazdpE2qMZpmi1JMyecRHCpCRXC1TnziJ2Jc+6eI8ey8LzYD2RY +TvuAgSnoW+za8Ac6M9WewI0j1xggp2R/WnbNfNMPb8uAcP9R3wIzIO2SRfAUe/CFA AxWq/jTiXNVfxFsJjFKbaR5UIasOJh0UQB+1HrLUZtxghRNkkPaGelzqoc96uG+dAC FIXe9r2beSh7lrwl4cl3lNd60vtGaUrrDXJyrF7DYLMOSBLsbuvmMfbtr4TFA/mFLO vrjv528ZHjJ7w== Date: Wed, 17 Apr 2024 09:35:49 +0100 From: Simon Horman To: Eric Dumazet Cc: "David S. Miller" , Jakub Kicinski , Paolo Abeni , Jamal Hadi Salim , Cong Wang , Jiri Pirko , netdev@vger.kernel.org, eric.dumazet@gmail.com, Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= , cake@lists.bufferbloat.net Subject: Re: [PATCH net-next 02/14] net_sched: cake: implement lockless cake_dump() Message-ID: <20240417083549.GA3846178@kernel.org> References: <20240415132054.3822230-1-edumazet@google.com> <20240415132054.3822230-3-edumazet@google.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20240415132054.3822230-3-edumazet@google.com> + Toke Høiland-Jørgensen cake@lists.bufferbloat.net On Mon, Apr 15, 2024 at 01:20:42PM +0000, Eric Dumazet wrote: > Instead of relying on RTNL, cake_dump() can use READ_ONCE() > annotations, paired with WRITE_ONCE() ones in cake_change(). > > Signed-off-by: Eric Dumazet ... > @@ -2774,68 +2783,71 @@ static int cake_dump(struct Qdisc *sch, struct sk_buff *skb) > { > struct cake_sched_data *q = qdisc_priv(sch); > struct nlattr *opts; > + u16 rate_flags; > > opts = nla_nest_start_noflag(skb, TCA_OPTIONS); > if (!opts) > goto nla_put_failure; > > - if (nla_put_u64_64bit(skb, TCA_CAKE_BASE_RATE64, q->rate_bps, > - TCA_CAKE_PAD)) > + if (nla_put_u64_64bit(skb, TCA_CAKE_BASE_RATE64, > + READ_ONCE(q->rate_bps), TCA_CAKE_PAD)) > goto nla_put_failure; > > if (nla_put_u32(skb, TCA_CAKE_FLOW_MODE, > - q->flow_mode & CAKE_FLOW_MASK)) > + READ_ONCE(q->flow_mode) & CAKE_FLOW_MASK)) > goto nla_put_failure; Hi Eric, q->flow_mode is read twice in this function. Once here... > > - if (nla_put_u32(skb, TCA_CAKE_RTT, q->interval)) > + if (nla_put_u32(skb, TCA_CAKE_RTT, READ_ONCE(q->interval))) > goto nla_put_failure; > > - if (nla_put_u32(skb, TCA_CAKE_TARGET, q->target)) > + if (nla_put_u32(skb, TCA_CAKE_TARGET, READ_ONCE(q->target))) > goto nla_put_failure; > > - if (nla_put_u32(skb, TCA_CAKE_MEMORY, q->buffer_config_limit)) > + if (nla_put_u32(skb, TCA_CAKE_MEMORY, > + READ_ONCE(q->buffer_config_limit))) > goto nla_put_failure; > > + rate_flags = READ_ONCE(q->rate_flags); > if (nla_put_u32(skb, TCA_CAKE_AUTORATE, > - !!(q->rate_flags & CAKE_FLAG_AUTORATE_INGRESS))) > + !!(rate_flags & CAKE_FLAG_AUTORATE_INGRESS))) > goto nla_put_failure; > > if (nla_put_u32(skb, TCA_CAKE_INGRESS, > - !!(q->rate_flags & CAKE_FLAG_INGRESS))) > + !!(rate_flags & CAKE_FLAG_INGRESS))) > goto nla_put_failure; > > - if (nla_put_u32(skb, TCA_CAKE_ACK_FILTER, q->ack_filter)) > + if (nla_put_u32(skb, TCA_CAKE_ACK_FILTER, READ_ONCE(q->ack_filter))) > goto nla_put_failure; > > if (nla_put_u32(skb, TCA_CAKE_NAT, > - !!(q->flow_mode & CAKE_FLOW_NAT_FLAG))) > + !!(READ_ONCE(q->flow_mode) & CAKE_FLOW_NAT_FLAG))) > goto nla_put_failure; ... and once here. I am assuming that it isn't a big deal, but perhaps it is better to save q->flow_mode into a local variable. Also, more importantly, q->flow_mode does not seem to be handled using WRITE_ONCE() in cake_change(). It's a non-trivial case, which I guess is well served by a mechanism built around a local variable. ...