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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Sun, 13 May 2018 15:52:01 +0200
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Subject: Re: INFO: rcu detected stall in kfree_skbmem
To:     Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Cc:     Eric Dumazet <eric.dumazet@gmail.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>
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On Fri, May 11, 2018 at 10:42 PM, Marcelo Ricardo Leitner
<marcelo.leitner@gmail.com> wrote:
> 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?

We only know what's in the bug reports. Do the other ones have
reproducers? It can make sense to mark them as duplicates to not have
a placer of open bugs about the same root cause.