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Date:   Sat, 12 Aug 2023 16:02:10 +0200
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Subject: Re: [PATCH] init: Add lockdep annotation to kthreadd_done completer
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From:   Helge Deller <deller@gmx.de>
To:     Andrew Morton <akpm@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-kernel@vger.kernel.org, linux-parisc@vger.kernel.org,
        Mike Rapoport <rppt@kernel.org>
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Precedence: bulk

Hi Andrew,

On 8/11/23 19:44, Helge Deller wrote:
> On 8/11/23 18:43, Andrew Morton wrote:
>> On Fri, 11 Aug 2023 18:04:22 +0200 Helge Deller <deller@gmx.de> wrote:
>>
>>> Add the missing lockdep annotation to avoid this warning:
>>>
>>> =C2=A0 INFO: trying to register non-static key.
>>> =C2=A0 The code is fine but needs lockdep annotation, or maybe
>>> =C2=A0 you didn't initialize this object before use?
>>> =C2=A0 turning off the locking correctness validator.
>>> =C2=A0 CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.5.0-rc5+ #681
>>> =C2=A0 Hardware name: 9000/785/C3700
>>> =C2=A0 Backtrace:
>>> =C2=A0=C2=A0 [<000000004030bcd0>] show_stack+0x74/0xb0
>>> =C2=A0=C2=A0 [<0000000041469c7c>] dump_stack_lvl+0x104/0x180
>>> =C2=A0=C2=A0 [<0000000041469d2c>] dump_stack+0x34/0x48
>>> =C2=A0=C2=A0 [<000000004040e5b4>] register_lock_class+0xd24/0xd30
>>> =C2=A0=C2=A0 [<000000004040c21c>] __lock_acquire.isra.0+0xb4/0xac8
>>> =C2=A0=C2=A0 [<000000004040cd60>] lock_acquire+0x130/0x298
>>> =C2=A0=C2=A0 [<000000004146df54>] _raw_spin_lock_irq+0x60/0xb8
>>> =C2=A0=C2=A0 [<0000000041472044>] wait_for_completion+0xa0/0x2d0
>>> =C2=A0=C2=A0 [<000000004146b544>] kernel_init+0x48/0x3a8
>>> =C2=A0=C2=A0 [<0000000040302020>] ret_from_kernel_thread+0x20/0x28
>>>
>>> ...
>>>
>>> --- a/init/main.c
>>> +++ b/init/main.c
>>> @@ -682,6 +682,8 @@ noinline void __ref __noreturn rest_init(void)
>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct task_struct *tsk;
>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 int pid;
>>>
>>> +=C2=A0=C2=A0=C2=A0 init_completion(&kthreadd_done);
>>> +
>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 rcu_scheduler_starting();
>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /*
>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * We need to spawn init first so =
that it obtains pid 1, however
>>
>> This is pretty old code, as is the page_alloc_init_late() change.=C2=A0=
 Do
>> we know why this warning has just turned up lately?

[dropped Helge's assumptions that it's related to parisc's unusual
__ARCH_SPIN_LOCK_UNLOCKED_VAL value. It turned out to be wrong.

Now I was able to trace down why I see those lockdep warnings on parisc.
The short answer is:
On parisc the _initdata section lies outside of the usual kernel
_stext ... _end range. Lockdep calls static_obj() which currently assumes
that __initdata is inside that range and thus returns "false".
That's why lockdep then reports
	INFO: trying to register non-static key.
which is wrong.

Please drop those 3 lockdep patches from your mm-queue:

mm-add-lockdep-annotation-to-pgdat_init_all_done_comp-completer.patch
init-add-lockdep-annotation-to-kthreadd_done-completer.patch
watchdog-fix-lockdep-warning.patch

I'll send one single patch which fixes static_obj() instead.

Thanks,
Helge