Re: lockdep warning while booting POWER9 PowerNV

[Daniel Axtens]

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