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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Wed, 8 May 2019 14:37:44 +0200
Message-ID: <CACT4Y+bcdEg_M5RNVKQvYPVLs1skvatGW-yTht7yDexR=Hjnyw@mail.gmail.com>
Subject: Re: WARNING in untrack_pfn
To:     Julia Lawall <julia.lawall@lip6.fr>
Cc:     Pavel Machek <pavel@ucw.cz>,
        syzbot <syzbot+e1a4f80c370d2381e49f@syzkaller.appspotmail.com>,
        Borislav Petkov <bp@alien8.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Dave Jiang <dave.jiang@intel.com>,
        Haozhong Zhang <haozhong.zhang@intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>, jacek.anaszewski@gmail.com,
        LKML <linux-kernel@vger.kernel.org>, linux-leds@vger.kernel.org,
        Andy Lutomirski <luto@kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        rpurdie@rpsys.net,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        "the arch/x86 maintainers" <x86@kernel.org>
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From: Julia Lawall
Date: Fri, Apr 12, 2019 at 3:21 PM

> On Fri, 12 Apr 2019, Pavel Machek wrote:
>
> > On Fri 2019-04-12 04:42:01, syzbot wrote:
> > > syzbot has bisected this bug to:
> > >
> > > commit c68729119f4d2993bec3c9cb999ad76de5aeddba
> > > Author: Julia Lawall <Julia.Lawall@lip6.fr>
> > > Date:   Sat Jul 15 09:58:19 2017 +0000
> > >
> > >     leds: tlc591xx: add missing of_node_put
> > >
> > > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=12cda0f3200000
> > > start commit:   23203e3f Merge branch 'akpm' (patches from Andrew)
> > > git tree:       upstream
> > > final crash:    https://syzkaller.appspot.com/x/report.txt?x=11cda0f3200000
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=16cda0f3200000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=861a3573f4e78ba1
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=e1a4f80c370d2381e49f
> > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17836d15400000
> > >
> > > Reported-by: syzbot+e1a4f80c370d2381e49f@syzkaller.appspotmail.com
> > > Fixes: c68729119f4d ("leds: tlc591xx: add missing of_node_put")
> > >
> > > For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> >
> > Can you revert c68729119f4d2993bec3c9cb999ad76de5aeddba on master and
> > see  if it fixes the problem? Because this is hard to believe...
>
> Likewise, it seems hard to believe that the change is a problem.  But
> could the problem be elsewhere and triggered by this code?

Looking at the bisection log, this looks like a hard to reproduce,
flaky crash. Most likely the crash did not fire on one of the commits
and that diverted bisection in the wrong direction.