netdev - Re: INFO: rcu detected stall in ndisc_alloc

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Date:   Mon, 31 Dec 2018 09:24:16 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     syzbot <syzbot+ea7d9cb314b4ab49a18a@...kaller.appspotmail.com>,
        David Miller <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: INFO: rcu detected stall in ndisc_alloc_skb

On Mon, Dec 31, 2018 at 9:17 AM Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> wrote:
>
> On 2018/12/31 16:49, Dmitry Vyukov wrote:
> > On Mon, Dec 31, 2018 at 8:42 AM syzbot
> > <syzbot+ea7d9cb314b4ab49a18a@...kaller.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@...kaller.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().

Just a hypothesis. OOMs lead to arbitrary memory corruptions, so can
cause stalls as well. But can be what you said too. I just thought
that cleaner dashboard is more useful than a large assorted pile of
crashes. If you think it's actionable in some way, feel free to undup.