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Date:   Tue, 31 Mar 2020 11:57:37 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     syzbot <syzbot+e84d7ebd1361da13c356@syzkaller.appspotmail.com>
Cc:     bp@alien8.de, hpa@zytor.com, linux-kernel@vger.kernel.org,
        mingo@redhat.com, syzkaller-bugs@googlegroups.com,
        tglx@linutronix.de, x86@kernel.org
Subject: Re: INFO: trying to register non-static key in try_to_wake_up
Message-ID: <20200331095737.GO20730@hirez.programming.kicks-ass.net>
References: <000000000000ec257905a21f7415@google.com>
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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.

>  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>