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Subject: Re: INFO: rcu detected stall in ndisc_alloc_skb
To:     Dmitry Vyukov <dvyukov@google.com>,
        syzbot <syzbot+ea7d9cb314b4ab49a18a@syzkaller.appspotmail.com>
Cc:     David Miller <davem@davemloft.net>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        LKML <linux-kernel@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>,
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        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Linux-MM <linux-mm@kvack.org>
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From:   Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
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Date:   Mon, 31 Dec 2018 17:17:17 +0900
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On 2018/12/31 16:49, Dmitry Vyukov wrote:
> On Mon, Dec 31, 2018 at 8:42 AM syzbot
> <syzbot+ea7d9cb314b4ab49a18a@syzkaller.appspotmail.com> wrote:
>>
>> Hello,
>>
>> syzbot found the following crash on:
>>
>> HEAD commit:    ef4ab8447aa2 selftests: bpf: install script with_addr.sh
>> git tree:       bpf-next
>> console output: https://syzkaller.appspot.com/x/log.txt?x=14a28b6e400000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=7e7e2279c0020d5f
>> dashboard link: https://syzkaller.appspot.com/bug?extid=ea7d9cb314b4ab49a18a
>> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
>>
>> Unfortunately, I don't have any reproducer for this crash yet.
>>
>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> Reported-by: syzbot+ea7d9cb314b4ab49a18a@syzkaller.appspotmail.com
> 
> Since this involves OOMs and looks like a one-off induced memory corruption:
> 
> #syz dup: kernel panic: corrupted stack end in wb_workfn
> 

Why?

RCU stall in this case is likely to be latency caused by flooding of printk().