Re: [BUG report]sparse warnings on DEFINE_PER_CPU() symbols non-static

[Wanlong Gao <gaowanlong@cn.fujitsu.com>]

On 12/04/2013 06:25 AM, Tejun Heo wrote:
> Hello,
> 
> On Tue, Nov 26, 2013 at 11:37:03AM +0800, Wanlong Gao wrote:
>> If kernel config CONFIG_DEBUG_FORCE_WEAK_PER_CPU=y, then the sparse will report non-static
>> warnings like following:
>>
>>> /git/linux/fs/inode.c:74:8: warning: symbol 'nr_inodes' was not declared. Should it be static?
>>> /git/linux/fs/inode.c:75:8: warning: symbol 'nr_unused' was not declared. Should it be static?
>>>
>>> $ vi +74 fs/inode.c
>>>   73 
>>>   74 static DEFINE_PER_CPU(unsigned long, nr_inodes);
>>>   75 static DEFINE_PER_CPU(unsigned long, nr_unused);
>>>   76 
> 
> Hmmm, so, if FORCE_WEAK_PER_CPU is set or the arch needs WEAK_PER_CPU,
> DEFINE_PER_CPU() explodes into mind-bending series of definitions to
> ensure that the symbol is globally unique to avoid breaking weak decl
> requirements on a few archs.  In the process static is dropped from
> the actual declaration and it's apparently missing extern decl in
> front of it.
> 
> Does the following patch make it go away?

Goes away but comes new error:

/git/linux/fs/inode.c:74:8: error: symbol 'nr_inodes' redeclared with different type (originally declared at /git/linux/fs/inode.c:74) - different address spaces
/git/linux/fs/inode.c:75:8: error: symbol 'nr_unused' redeclared with different type (originally declared at /git/linux/fs/inode.c:75) - different address spaces
/git/linux/fs/inode.c:835:8: error: symbol 'last_ino' redeclared with different type (originally declared at /git/linux/fs/inode.c:835) - different address spaces


Thanks,
Wanlong Gao

> 
> Thanks.
> 
> diff --git a/include/linux/percpu-defs.h b/include/linux/percpu-defs.h
> index 57e890a..8c490cc 100644
> --- a/include/linux/percpu-defs.h
> +++ b/include/linux/percpu-defs.h
> @@ -69,6 +69,7 @@
>  	__PCPU_DUMMY_ATTRS char __pcpu_scope_##name;			\
>  	extern __PCPU_DUMMY_ATTRS char __pcpu_unique_##name;		\
>  	__PCPU_DUMMY_ATTRS char __pcpu_unique_##name;			\
> +	extern __typeof__(type) name;					\
>  	__PCPU_ATTRS(sec) PER_CPU_DEF_ATTRIBUTES __weak			\
>  	__typeof__(type) name
>  #else
>