From mboxrd@z Thu Jan 1 00:00:00 1970 From: Phil Sutter Subject: Re: [net-next PATCH 3/3] qdisc: catch misconfig of attaching qdisc to tx_queue_len zero device Date: Fri, 4 Nov 2016 11:59:13 +0100 Message-ID: <20161104105913.GN5640@orbyte.nwl.cc> References: <20161103135534.28737.37657.stgit@firesoul> <20161103135611.28737.39840.stgit@firesoul> <20161104093526.GM5640@orbyte.nwl.cc> <20161104111042.12a361ca@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@vger.kernel.org, Robert Olsson , Jamal Hadi Salim To: Jesper Dangaard Brouer Return-path: Received: from orbyte.nwl.cc ([151.80.46.58]:37635 "EHLO mail.nwl.cc" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760618AbcKDK7Q (ORCPT ); Fri, 4 Nov 2016 06:59:16 -0400 Content-Disposition: inline In-Reply-To: <20161104111042.12a361ca@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: On Fri, Nov 04, 2016 at 11:10:42AM +0100, Jesper Dangaard Brouer wrote: > > On Fri, 4 Nov 2016 10:35:26 +0100 Phil Sutter wrote: > > > Hi, > > > > On Thu, Nov 03, 2016 at 02:56:11PM +0100, Jesper Dangaard Brouer wrote: > > [...] > > > diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c > > > index 206dc24add3a..f337f1bdd1d4 100644 > > > --- a/net/sched/sch_api.c > > > +++ b/net/sched/sch_api.c > > > @@ -960,6 +960,17 @@ static struct Qdisc *qdisc_create(struct net_device *dev, > > > > > > sch->handle = handle; > > > > > > + /* This exist to keep backward compatible with a userspace > > > + * loophole, what allowed userspace to get IFF_NO_QUEUE > > > + * facility on older kernels by setting tx_queue_len=0 (prior > > > + * to qdisc init), and then forgot to reinit tx_queue_len > > > + * before again attaching a qdisc. > > > + */ > > > + if ((dev->priv_flags & IFF_NO_QUEUE) && (dev->tx_queue_len == 0)) { > > > + dev->tx_queue_len = DEFAULT_TX_QUEUE_LEN; > > > + netdev_info(dev, "Caught tx_queue_len zero misconfig\n"); > > > + } > > > > I wonder why this is limited to IFF_NO_QUEUE devices. Do you think there > > is a valid use case for physical ones? > > Hmmm, I cannot come up with a useful use-case for physical devices, but > I cannot see why we should save users that had used the loophole on > physical devices, as that is clearly a faulty config to begin with. > See net_crit_ratelimited warning here: > https://github.com/torvalds/linux/blob/v4.9-rc3/net/core/dev.c#L3403 I really feel like nit-picking again, but what differs in between loophole users of virtual devices (whose broken scripts stopped working) and loophole users of physical devices (whose broken scripts stopped working as well)? I we really take exposing broken userspace scripts as kernel bugs, don't we have to take this one for the same as well? > > Also, if we sanitize here, couldn't we then just get rid of the > > sanitization you're fixing in patch 2? > > Without patch 2, then some IFF_NO_QUEUE devices would have a visible > tx_queue_len 0 (e.g. the ones not calling ether_setup()), and that > would be inconsistent (visible from userspace). Ah, indeed. Although there's no functional difference, I guess it might confuse people seeing an interface with 0 qlen performing properly. Thanks, Phil