linux-kernel - Re: WARNING in rcu_check_gp_start

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Message-ID: <20190223103809.GB23376@zn.tnic>
Date:   Sat, 23 Feb 2019 11:38:09 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     syzbot <syzbot+111bc509cd9740d7e4aa@...kaller.appspotmail.com>,
        Dou Liyang <douly.fnst@...fujitsu.com>,
        "H. Peter Anvin" <hpa@...or.com>, konrad.wilk@...cle.com,
        Len Brown <len.brown@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>, puwen@...on.cn,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Thomas Gleixner <tglx@...utronix.de>, wang.yi59@....com.cn,
        the arch/x86 maintainers <x86@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: WARNING in rcu_check_gp_start_stall

On Sat, Feb 23, 2019 at 11:33:33AM +0100, Dmitry Vyukov wrote:
> On Fri, Feb 22, 2019 at 11:20 PM Borislav Petkov <bp@...en8.de> wrote:
> >
> > On Fri, Feb 22, 2019 at 09:10:04AM -0800, syzbot wrote:
> > > Hello,
> > >
> > > syzbot found the following crash on:
> > >
> > > HEAD commit:    8a61716ff2ab Merge tag 'ceph-for-5.0-rc8' of git://github...
> > > git tree:       upstream
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=1531dd3f400000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=7132344728e7ec3f
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=111bc509cd9740d7e4aa
> > > compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16d4966cc00000
> > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10c492d0c00000
> >
> > So I ran this for more than an hour in a guest here with the above
> > .config but nothing happened. The compiler I used is 8.2, dunno of that
> > makes the difference or I'm missing something else...
> 
> I was able to reproduce this on the first run:
> 
> # ./syz-execprog -procs=8 -repeat=0 hang

Ok, this is what I'm missing: I ran the reproducer directly but you run
a multithreaded thing with this syz-execprog. Where do I get that syz-
thing?

> There is a bunch of other bug reports about hangs where reproducers
> mention perf_event_open and sched_setattr.

This is a known issue, says peterz.

-- 
Regards/Gruss,
    Boris.

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