linux-kernel - Re: lockdep warning while booting POWER9 PowerNV

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Date:   Mon, 25 Nov 2019 16:01:13 +1100
From:   Michael Ellerman <michael@...erman.id.au>
To:     Daniel Axtens <dja@...ens.net>,
        Michael Ellerman <mpe@...erman.id.au>,
        Bart Van Assche <bvanassche@....org>, Qian Cai <cai@....pw>
CC:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: lockdep warning while booting POWER9 PowerNV



On 25 November 2019 12:12:01 pm AEDT, Daniel Axtens <dja@...ens.net> wrote:
>Hi Michael,
>
>>>> Once in a while, booting an IBM POWER9 PowerNV system (8335-GTH)
>would generate
>>>> a warning in lockdep_register_key() at,
>>>> 
>>>> if (WARN_ON_ONCE(static_obj(key)))
>>>> 
>>>> because
>>>> 
>>>> key = 0xc0000000019ad118
>>>> &_stext = 0xc000000000000000
>>>> &_end = 0xc0000000049d0000
>>>> 
>>>> i.e., it will cause static_obj() returns 1.
>>>
>>> (back from a trip)
>>>
>>> Hi Qian,
>>>
>>> Does this mean that on POWER9 it can happen that a dynamically
>allocated 
>>> object has an address that falls between &_stext and &_end?
>>
>> I thought that was true on all arches due to initmem, but seems not.
>>
>> I guess we have the same problem as s390 and we need to define
>> arch_is_kernel_initmem_freed().
>>
>> Qian, can you try this:
>>
>> diff --git a/arch/powerpc/include/asm/sections.h
>b/arch/powerpc/include/asm/sections.h
>> index 4a1664a8658d..616b1b7b7e52 100644
>> --- a/arch/powerpc/include/asm/sections.h
>> +++ b/arch/powerpc/include/asm/sections.h
>> @@ -5,8 +5,22 @@
>>  
>>  #include <linux/elf.h>
>>  #include <linux/uaccess.h>
>> +
>> +#define arch_is_kernel_initmem_freed arch_is_kernel_initmem_freed
>> +
>>  #include <asm-generic/sections.h>
>>  
>> +extern bool init_mem_is_free;
>> +
>> +static inline int arch_is_kernel_initmem_freed(unsigned long addr)
>> +{
>> +	if (!init_mem_is_free)
>> +		return 0;
>> +
>> +	return addr >= (unsigned long)__init_begin &&
>> +		addr < (unsigned long)__init_end;
>> +}
>> +
>>  extern char __head_end[];
>>  
>>  #ifdef __powerpc64__
>>
>
>This also fixes the following syzkaller bug:
>https://syzkaller-ppc64.appspot.com/bug?id=cfdf75cd985012d0124cd41e6fa095d33e7d0f6b
>https://github.com/linuxppc/issues/issues/284
>
>Would you like me to do up a nice commit message for it?

That'd be great, thanks.

cheers