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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Tue, 31 Mar 2020 12:18:49 +0200
Message-ID: <CACT4Y+bqBCqDPQZ1Nk8G+8y2vu8aaT2S54J4UqRPaFNUcusbYw@mail.gmail.com>
Subject: Re: INFO: trying to register non-static key in try_to_wake_up
To:     Peter Zijlstra <peterz@infradead.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        DRI <dri-devel@lists.freedesktop.org>,
        Linux Fbdev development list <linux-fbdev@vger.kernel.org>
Cc:     syzbot <syzbot+e84d7ebd1361da13c356@syzkaller.appspotmail.com>,
        Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        "the arch/x86 maintainers" <x86@kernel.org>
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Sender: linux-kernel-owner@vger.kernel.org
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On Tue, Mar 31, 2020 at 11:57 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Mon, Mar 30, 2020 at 10:01:12PM -0700, syzbot wrote:
> > Hello,
> >
> > syzbot found the following crash on:
> >
> > HEAD commit:    9420e8ad Merge tag 'for-linus' of git://git.kernel.org/pub..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=1206ed4be00000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=27392dd2975fd692
> > dashboard link: https://syzkaller.appspot.com/bug?extid=e84d7ebd1361da13c356
> > compiler:       gcc (GCC) 9.0.0 20181231 (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+e84d7ebd1361da13c356@syzkaller.appspotmail.com
> >
> > INFO: trying to register non-static key.
> > the code is fine but needs lockdep annotation.
> > turning off the locking correctness validator.
> > CPU: 1 PID: 1014 Comm: syz-executor.0 Not tainted 5.6.0-rc7-syzkaller #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> > Call Trace:
> >  <IRQ>
> >  __dump_stack lib/dump_stack.c:77 [inline]
> >  dump_stack+0x188/0x20d lib/dump_stack.c:118
> >  assign_lock_key kernel/locking/lockdep.c:880 [inline]
> >  register_lock_class+0x14c4/0x1540 kernel/locking/lockdep.c:1189
> >  __lock_acquire+0xfc/0x3ca0 kernel/locking/lockdep.c:3836
> >  lock_acquire+0x197/0x420 kernel/locking/lockdep.c:4484
> >  __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> >  _raw_spin_lock_irqsave+0x8c/0xbf kernel/locking/spinlock.c:159
> >  try_to_wake_up+0x9f/0x17c0 kernel/sched/core.c:2547
>
> That's p->pi_lock, which gets initialized in rt_mutex_init_task() in
> copy_process(). This should be impossible. Very odd.

The stack mentions fbdev, which is a red flag at the moment. There are
a dozen of bad bugs in fbdev and around. Just few days ago Andy
pointed to another "impossible" crash "general protection fault in
do_syscall_64" which is related to dri:
https://syzkaller.appspot.com/bug?id=0ec7b2602b1ff40f0d34f38baa4ba1640727c3d9
https://groups.google.com/forum/#!msg/syzkaller-bugs/ePqhfYx0-8M/Q_Urt97iAAAJ

There are probably more random manifestations of these bugs already,
and I guess we will be getting more.

+fbdev maintainers


> >  wake_up_worker kernel/workqueue.c:836 [inline]
> >  insert_work+0x2ad/0x3a0 kernel/workqueue.c:1337
> >  __queue_work+0x50d/0x1280 kernel/workqueue.c:1488
> >  call_timer_fn+0x195/0x760 kernel/time/timer.c:1404
> >  expire_timers kernel/time/timer.c:1444 [inline]
> >  __run_timers kernel/time/timer.c:1773 [inline]
> >  __run_timers kernel/time/timer.c:1740 [inline]
> >  run_timer_softirq+0x412/0x1600 kernel/time/timer.c:1786
> >  __do_softirq+0x26c/0x99d kernel/softirq.c:292
> >  invoke_softirq kernel/softirq.c:373 [inline]
> >  irq_exit+0x192/0x1d0 kernel/softirq.c:413
> >  exiting_irq arch/x86/include/asm/apic.h:546 [inline]
> >  smp_apic_timer_interrupt+0x19e/0x600 arch/x86/kernel/apic/apic.c:1146
> >  apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:829
> >  </IRQ>
>
> --
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