Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Fri, 11 May 2018 17:42:28 -0300
From:   Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
To:     Eric Dumazet <eric.dumazet@gmail.com>
Cc:     Dmitry Vyukov <dvyukov@google.com>,
        syzbot <syzbot+fc78715ba3b3257caf6a@syzkaller.appspotmail.com>,
        Vladislav Yasevich <vyasevich@gmail.com>,
        Neil Horman <nhorman@tuxdriver.com>,
        linux-sctp@vger.kernel.org, Andrei Vagin <avagin@virtuozzo.com>,
        David Miller <davem@davemloft.net>,
        Kirill Tkhai <ktkhai@virtuozzo.com>,
        LKML <linux-kernel@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>
Subject: Re: INFO: rcu detected stall in kfree_skbmem
Message-ID: <20180511204228.GO4977@localhost.localdomain>
References: <000000000000a9b0e3056b14bfb2@google.com>
 <CACT4Y+Z_+=VLbELVW69B7WEVqvri1xBMM5RMnMQynec_XgaE=w@mail.gmail.com>
 <20180511184141.GW5105@localhost.localdomain>
 <683d1ead-d35b-27ee-0f0c-f7e815d989fc@gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <683d1ead-d35b-27ee-0f0c-f7e815d989fc@gmail.com>
User-Agent: Mutt/1.9.2 (2017-12-15)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, May 11, 2018 at 12:08:33PM -0700, Eric Dumazet wrote:
>
>
> On 05/11/2018 11:41 AM, Marcelo Ricardo Leitner wrote:
>
> > But calling ip6_xmit with rcu_read_lock is expected. tcp stack also
> > does it.
> > Thus I think this is more of an issue with IPv6 stack. If a host has
> > an extensive ip6tables ruleset, it probably generates this more
> > easily.
> >
> >>>  sctp_v6_xmit+0x4a5/0x6b0 net/sctp/ipv6.c:225
> >>>  sctp_packet_transmit+0x26f6/0x3ba0 net/sctp/output.c:650
> >>>  sctp_outq_flush+0x1373/0x4370 net/sctp/outqueue.c:1197
> >>>  sctp_outq_uncork+0x6a/0x80 net/sctp/outqueue.c:776
> >>>  sctp_cmd_interpreter net/sctp/sm_sideeffect.c:1820 [inline]
> >>>  sctp_side_effects net/sctp/sm_sideeffect.c:1220 [inline]
> >>>  sctp_do_sm+0x596/0x7160 net/sctp/sm_sideeffect.c:1191
> >>>  sctp_generate_heartbeat_event+0x218/0x450 net/sctp/sm_sideeffect.c:406
> >>>  call_timer_fn+0x230/0x940 kernel/time/timer.c:1326
> >>>  expire_timers kernel/time/timer.c:1363 [inline]
> >
> > Having this call from a timer means it wasn't processing sctp stack
> > for too long.
> >
>
> I feel the problem is that this part is looping, in some infinite loop.
>
> I have seen this stack traces in other reports.

Checked mail history now, seems at least two other reports on RCU
stalls had sctp_generate_heartbeat_event involved.

>
> Maybe some kind of list corruption.

Could be.
Do we know if it generated a flood of packets?

  Marcelo