From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jiri Pirko Subject: Re: RCU callback crashes Date: Wed, 20 Dec 2017 21:15:55 +0100 Message-ID: <20171220201555.GF1760@nanopsycho> References: <20171219175921.7db9b0e1@cakuba.netronome.com> <20171220061118.GB1916@nanopsycho> <20171219222227.402e684a@cakuba.netronome.com> <20171219223404.03786d66@cakuba.netronome.com> <20171220195922.GB1760@nanopsycho> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jakub Kicinski , "netdev@vger.kernel.org" , john.fastabend@gmail.com To: Cong Wang Return-path: Received: from mail-wm0-f68.google.com ([74.125.82.68]:39409 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755939AbdLTUP6 (ORCPT ); Wed, 20 Dec 2017 15:15:58 -0500 Received: by mail-wm0-f68.google.com with SMTP id i11so11971914wmf.4 for ; Wed, 20 Dec 2017 12:15:58 -0800 (PST) Content-Disposition: inline In-Reply-To: <20171220195922.GB1760@nanopsycho> Sender: netdev-owner@vger.kernel.org List-ID: Wed, Dec 20, 2017 at 08:59:22PM CET, jiri@resnulli.us wrote: >Wed, Dec 20, 2017 at 07:17:50PM CET, xiyou.wangcong@gmail.com wrote: >>On Tue, Dec 19, 2017 at 10:34 PM, Jakub Kicinski wrote: >>> Ah, no object debug but KASAN on produces this: >>> >> >> >>I bet it is an ingress qdisc which is being freed? >> >> >> >>> [ 39.268209] BUG: KASAN: use-after-free in cpu_needs_another_gp+0x246/0x2b0 >>> [ 39.275965] Read of size 8 at addr ffff8803aa64f138 by task swapper/13/0 >>> [ 39.283524] >>> [ 39.285256] CPU: 13 PID: 0 Comm: swapper/13 Not tainted 4.15.0-rc3-perf-00955-g1d0b01347dd5-dirty #8 >>> [ 39.295535] Hardware name: Dell Inc. PowerEdge R730/072T6D, BIOS 2.3.4 11/08/2016 >>> [ 39.303969] Call Trace: >>> [ 39.306769] >>> [ 39.309088] dump_stack+0xa6/0x118 >>> [ 39.312957] ? _atomic_dec_and_lock+0xe8/0xe8 >>> [ 39.317895] ? cpu_needs_another_gp+0x246/0x2b0 >>> [ 39.323030] print_address_description+0x6a/0x270 >>> [ 39.328380] ? cpu_needs_another_gp+0x246/0x2b0 >>> [ 39.333510] kasan_report+0x23f/0x350 >>> [ 39.337672] cpu_needs_another_gp+0x246/0x2b0 >>> ... >>> [ 39.383026] rcu_process_callbacks+0x1a0/0x620 >>> ... >> >> >>This is confusing. >> >>I guess it is q->miniqp which is freed in qdisc_graft() without properly >>waiting for rcu readers? > >miniqp is inside qdisc private data: >struct ingress_sched_data { > struct tcf_block *block; > struct tcf_block_ext_info block_info; > struct mini_Qdisc_pair miniqp; >}; > >That is freed along with the qdisc itself in: >qdisc_destroy->qdisc_free > >Before miniq, tp was checked in the rcu reader path. In case it was not >null, q was processed. In slow patch, tp is freed after rcu grace period: >tcf_proto_destroy->kfree_rcu > >I assumed that since q is processed in rcu reader, it is also freed after >a grace period, but now looking at the code I don't see it happening >like that. Aha! It was removed by: commit c5ad119fb6c09b0297446be05bd66602fa564758 Author: John Fastabend Date: Thu Dec 7 09:58:19 2017 -0800 net: sched: pfifo_fast use skb_array > >So I think that change to miniq made the existing race window >a bit wider and easier to hit. > >I believe that calling kfree_rcu by call_rcu should resolve this.