linux-kernel - Re: INFO: rcu detected stall in xfrm_confirm

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Date:   Mon, 19 Feb 2018 11:05:38 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Steffen Klassert <steffen.klassert@...unet.com>
Cc:     syzbot <syzbot+7d03c810e50aaedef98a@...kaller.appspotmail.com>,
        dzickus@...hat.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>, npiggin@...il.com,
        Philippe Ombredanne <pombredanne@...b.com>,
        syzkaller-bugs@...glegroups.com,
        Thomas Gleixner <tglx@...utronix.de>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>
Subject: Re: INFO: rcu detected stall in xfrm_confirm_neigh

On Mon, Feb 19, 2018 at 8:22 AM, Steffen Klassert
<steffen.klassert@...unet.com> wrote:
>> > <syzbot+7d03c810e50aaedef98a@...kaller.appspotmail.com> wrote:
>> >> Hello,
>> >>
>> >> syzbot hit the following crash on net-next commit
>> >> 9515a2e082f91457db0ecff4b65371d0fb5d9aad (Thu Jan 25 03:37:38 2018 +0000)
>> >> net/ipv4: Allow send to local broadcast from a socket bound to a VRF
>> >>
>> >> So far this crash happened 6 times on net-next.
>> >> Unfortunately, I don't have any reproducer for this crash yet.
>> >> Raw console output is attached.
>> >> compiler: gcc (GCC) 7.1.1 20170620
>> >> .config is attached.
>> >
>> >
>> > +xfrm maintainers
>>
>> Here is a C repro:
>> https://gist.githubusercontent.com/dvyukov/92c67ba9afaaa960bcfbdc6ef549ac10/raw/786f9221c1d707c7f4a15effcb1d5997dd4f8638/gistfile1.txt
>
> Seems like syzbot does not know about this reproducer.
>
> I've send a patch to test and got this as the reply:
>
> This crash does not have a reproducer. I cannot test it.

Yes, it does not know about the reproducer. I've extracted it
manually, these hangs are sometimes hard to reproduce. For syzbot this
bug does not have a reproducer.
Have you tried to run the reproducer? For me it reproduced the bug
quite reliably.