linux-kernel - Re: WARNING in rcu_check_gp_start

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Date:   Mon, 18 Mar 2019 13:18:04 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     syzbot <syzbot+111bc509cd9740d7e4aa@...kaller.appspotmail.com>,
        Borislav Petkov <bp@...en8.de>,
        "open list:ANDROID DRIVERS" <devel@...verdev.osuosl.org>,
        Dou Liyang <douly.fnst@...fujitsu.com>,
        forest@...ttletooquiet.net, "H. Peter Anvin" <hpa@...or.com>,
        konrad.wilk@...cle.com, Len Brown <len.brown@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, puwen@...on.cn,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Thomas Gleixner <tglx@...utronix.de>, tvboxspy@...il.com,
        wang.yi59@....com.cn, "the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: WARNING in rcu_check_gp_start_stall

On Sun, Mar 17, 2019 at 12:04 PM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Sun, Mar 17, 2019 at 03:43:01AM -0700, syzbot wrote:
> > syzbot has bisected this bug to:
> >
> > commit f1e3e92135202ff3d95195393ee62808c109208c
> > Author: Malcolm Priestley <tvboxspy@...il.com>
> > Date:   Wed Jul 22 18:16:42 2015 +0000
> >
> >     staging: vt6655: fix tagSRxDesc -> next_desc type
> >
> > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=111856cf200000
> > start commit:   f1e3e921 staging: vt6655: fix tagSRxDesc -> next_desc type
> > git tree:       upstream
> > final crash:    https://syzkaller.appspot.com/x/report.txt?x=131856cf200000
> > console output: https://syzkaller.appspot.com/x/log.txt?x=151856cf200000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=7132344728e7ec3f
> > dashboard link: https://syzkaller.appspot.com/bug?extid=111bc509cd9740d7e4aa
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16d4966cc00000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10c492d0c00000
> >
> > Reported-by: syzbot+111bc509cd9740d7e4aa@...kaller.appspotmail.com
> > Fixes: f1e3e921 ("staging: vt6655: fix tagSRxDesc -> next_desc type")
>
> I think syzbot is a bit confused here, how can this simple patch, where
> you do not have the hardware for this driver, cause this problem?

Yes, I guess so.
This perf_event_open+sched_setattr combo bug causes problems with
hangs at random places, developers looking at these hangs again and
again, incorrect bisection. I would be useful if somebody
knowledgeable in perf/sched look at it.