Re: [PATCH] fix vmstat per cpu usage

[Jan Blunck <jblunck@suse.de>]

On Tue, Aug 01, Andrew Morton wrote:

> >  
> >  static inline void __count_vm_event(enum vm_event_item item)
> >  {
> > -	__get_cpu_var(vm_event_states.event[item])++;
> > +	__get_cpu_var(vm_event_states).event[item]++;
> >  }
> 
> How odd.  Are there any negative consequences to the existing code?

In asm-s390/percpu.h we use

 #define __get_cpu_var(var) __reloc_hide(var,S390_lowcore.percpu_offset)

and for modules on s390x __reloc_hide() is defined as

 #define __reloc_hide(var,offset) \
   (*({ unsigned long *__ptr; \
        asm ( "larl %0,per_cpu__"#var"@GOTENT" \
              : "=a" (__ptr) : "X" (per_cpu__##var) ); \
        (typeof(&per_cpu__##var))((*__ptr) + (offset)); }))

which leads in this case to

 larl %0, per_cpu__vm_event_states.event[item]@GOTENT

which is invalid asm.