From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752218AbcHLO03 (ORCPT ); Fri, 12 Aug 2016 10:26:29 -0400 Received: from www62.your-server.de ([213.133.104.62]:47212 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751022AbcHLO01 (ORCPT ); Fri, 12 Aug 2016 10:26:27 -0400 Message-ID: <57ADDC8B.9010700@iogearbox.net> Date: Fri, 12 Aug 2016 16:26:19 +0200 From: Daniel Borkmann User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Jiri Kosina CC: Eric Dumazet , Jamal Hadi Salim , Phil Sutter , Cong Wang , David Miller , linux-kernel@vger.kernel.org, netdev@vger.kernel.org Subject: Re: [PATCH 2/2] net: sched: convert qdisc linked list to hashtable References: <57ADC6AA.5070506@iogearbox.net> In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Authenticated-Sender: daniel@iogearbox.net Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/12/2016 03:53 PM, Jiri Kosina wrote: > On Fri, 12 Aug 2016, Daniel Borkmann wrote: > >> This results in below panic. Tested reverting this patch and it fixes >> the panic. >> >> Did you test this also with ingress or clsact qdisc (just try adding >> it to lo dev for example) ? > > Hi Daniel, > > thanks for the report. Hmm, I am pretty sure clsact worked for me, but > I'll recheck. > >> What happens is the following in qdisc_match_from_root(): >> >> [ 995.422187] XXX qdisc:ffff88025e4fc800 queue:ffff880262759000 >> dev:ffff880261cc2000 handle:ffff0000 >> [ 995.422200] XXX qdisc:ffffffff81cf8100 queue:ffffffff81cf8240 dev: >> (null) handle:ffff0000 >> >> I believe this is due to dev_ingress_queue_create() assigning the >> global noop_qdisc instance as qdisc_sleeping, which later qdisc_lookup() >> uses for qdisc_match_from_root(). >> >> But everything that uses things like noop_qdisc cannot work with the >> new qdisc_match_from_root(), because qdisc_dev(root) will always trigger >> NULL pointer dereference there. Reason is because the dev is always >> NULL for noop, it's a singleton, see noop_qdisc and noop_netdev_queue >> in sch_generic.c. >> >> Now how to fix it? Creating separate noop instances each time it's set >> would be quite a waste of memory. Even fuglier would be to hack a static >> net device struct into sch_generic.c and let noop_netdev_queue point there >> to get to the hash table. Or we just not use qdisc_dev(). > > How about we actually extend a little bit the TCQ_F_BUILTIN special case > test in qdisc_match_from_root()? > > After the change, the only way how qdisc_dev() could be NULL should be a > TCQ_F_BUILTIN case, right? > > I was thinking about something like the patch below (the reasong being > that ->dev would be NULL only in cases of singletonish qdiscs) ... > wouldn't that also fix the issue you're seeing? Have to think it through a > little bit more .. Ahh, so this has the same effect as previously observed with the other fix. Perhaps it's just a dumping issue, but to the below clsact, there shouldn't be pfifo_fast instances appearing. # tc qdisc show dev wlp2s0b1 qdisc mq 0: root qdisc pfifo_fast 0: parent :4 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1 qdisc pfifo_fast 0: parent :3 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1 qdisc pfifo_fast 0: parent :2 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1 qdisc pfifo_fast 0: parent :1 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1 # tc qdisc add dev wlp2s0b1 clsact # tc qdisc show dev wlp2s0b1 qdisc mq 0: root qdisc pfifo_fast 0: parent :4 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1 qdisc pfifo_fast 0: parent :3 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1 qdisc pfifo_fast 0: parent :2 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1 qdisc pfifo_fast 0: parent :1 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1 qdisc clsact ffff: parent ffff:fff1 qdisc pfifo_fast 0: parent :4 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1 qdisc pfifo_fast 0: parent :3 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1 qdisc pfifo_fast 0: parent :2 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1 qdisc pfifo_fast 0: parent :1 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1 > diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c > index 25aada7..1c9faed 100644 > --- a/net/sched/sch_api.c > +++ b/net/sched/sch_api.c > @@ -260,6 +260,9 @@ static struct Qdisc *qdisc_match_from_root(struct Qdisc *root, u32 handle) > { > struct Qdisc *q; > > + if (!qdisc_dev(root)) > + return (root->handle == handle ? root : NULL); > + > if (!(root->flags & TCQ_F_BUILTIN) && > root->handle == handle) > return root; > > > Thanks! >