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SubjectRe: lockdep warning while booting POWER9 PowerNV
Date
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?

Regards,
Daniel

>
> cheers

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