From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1756643AbdLVTEt (ORCPT <rfc822;w@1wt.eu>);
        Fri, 22 Dec 2017 14:04:49 -0500
Received: from mx1.redhat.com ([209.132.183.28]:44660 "EHLO mx1.redhat.com"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1753948AbdLVTEp (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Fri, 22 Dec 2017 14:04:45 -0500
Date: Fri, 22 Dec 2017 17:04:37 -0200
From: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: David Ahern <dsahern@gmail.com>,
        syzbot 
        <bot+21b498fc12cf2041655f8e1eeae0733807d794b3@syzkaller.appspotmail.com>,
        LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>, syzkaller-bugs@googlegroups.com,
        David Miller <davem@davemloft.net>, Florian Westphal <fw@strlen.de>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Xin Long <lucien.xin@gmail.com>, jakub.kicinski@netronome.com,
        mschiffer@universe-factory.net,
        Vladislav Yasevich <vyasevich@gmail.com>, Jiri Benc <jbenc@redhat.com>,
        netdev <netdev@vger.kernel.org>, Neil Horman <nhorman@tuxdriver.com>,
        linux-sctp@vger.kernel.org
Subject: Re: INFO: task hung in bpf_exit_net
Message-ID: <20171222190437.GC6123@localhost.localdomain>
References: <001a1143fd00a8cc790560b0b552@google.com>
 <CACT4Y+Ze8t3ipFyhfy9XfmvUw4tob+dAUiVMQ-xHimYDXpSiRw@mail.gmail.com>
 <f519a1f0-8166-027e-e063-13aa718ce4e4@gmail.com>
 <CACT4Y+aaSX4S3KHJjqkiQhhOZAtEN_fMD1m_Ve3rz4u4x9KSWg@mail.gmail.com>
 <20171222182807.GC32765@localhost.localdomain>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20171222182807.GC32765@localhost.localdomain>
User-Agent: Mutt/1.9.1 (2017-09-22)
X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Fri, 22 Dec 2017 19:04:45 +0000 (UTC)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Fri, Dec 22, 2017 at 04:28:07PM -0200, Marcelo Ricardo Leitner wrote:
> On Fri, Dec 22, 2017 at 11:58:08AM +0100, Dmitry Vyukov wrote:
> ...
> > > Same with this one, perhaps related to / fixed by:
> > >     http://patchwork.ozlabs.org/patch/850957/
> > >
> > 
> > 
> > 
> > Looking at the log, this one seems to be an infinite loop in SCTP code
> > with console output in it. Kernel is busy printing gazilion of:
> > 
> > [  176.491099] sctp: sctp_transport_update_pmtu: Reported pmtu 508 too
> > low, using default minimum of 512
> > ** 110 printk messages dropped **
> > [  176.503409] sctp: sctp_transport_update_pmtu: Reported pmtu 508 too
> > low, using default minimum of 512
> > ** 103 printk messages dropped **
> > ...
> > [  246.742374] sctp: sctp_transport_update_pmtu: Reported pmtu 508 too
> > low, using default minimum of 512
> > [  246.742484] sctp: sctp_transport_update_pmtu: Reported pmtu 508 too
> > low, using default minimum of 512
> > [  246.742590] sctp: sctp_transport_update_pmtu: Reported pmtu 508 too
> > low, using default minimum of 512
> > 
> > Looks like a different issue.
> > 
> 
> Oh. I guess this is caused by the interface having a MTU smaller than
> SCTP_DEFAULT_MINSEGMENT (512), as the icmp frag needed handler
> (sctp_icmp_frag_needed) will trigger an instant retransmission.
> But as the MTU is smaller, SCTP won't update it, but will issue the
> retransmission anyway.
> 
> I will test this soon. Should be fairly easy to trigger it.

Reproduced it.

netns A veth0(1500) - veth1(1500) B veth2(508) - veth3(508) C

When A sends a sctp packet bigger than 508, it triggers the issue as B
will reply a icmp frag needed with a size that sctp won't accept but
will retransmit anyway.

  Marcelo