Re: [PATCH] perf: Fix perf_event_{init,exit}_cpu stubs

[Peter Zijlstra]

On Thu, Nov 03, 2022 at 03:43:03PM -0700, Florian Fainelli wrote:
> The original commit that introduced those stubs was already at fault,
> but in the absence of a caller of perf_event_{init,exit}_cpu outside of
> code that is compiled regardless of CONFIG_PERF_EVENTS, the build
> failure cannot be observed. This was observed with the Android kernel to
> produce a build failure similar to this:
> 
>     In file included from ./include/uapi/linux/posix_types.h:5,
>                      from ./include/uapi/linux/types.h:14,
>                      from ./include/linux/types.h:6,
>                      from ./include/linux/limits.h:6,
>                      from ./include/linux/kernel.h:7,
>                      from ./include/linux/sched/mm.h:5,
>                      from kernel/cpu.c:6:
>     kernel/cpu.c: In function 'random_and_perf_prepare_fusion':
>     ./include/linux/stddef.h:8:14: error: called object is not a function or function pointer
>      #define NULL ((void *)0)
>                   ^
>     ./include/linux/perf_event.h:1607:29: note: in expansion of macro 'NULL'
>      #define perf_event_init_cpu NULL
>                                  ^~~~
>     kernel/cpu.c:1686:2: note: in expansion of macro 'perf_event_init_cpu'
>       perf_event_init_cpu(cpu);
>       ^~~~~~~~~~~~~~~~~~~

What is the actual problem reported here? Did you see all the other NULL
assignments in cpuhp_hp_states ?

> 
> Fixes: 00e16c3d68fc ("perf/core: Convert to hotplug state machine")
> Reported-by: Anand Gore <anand.gore@xxxxxxxxxxxx>
> Signed-off-by: Florian Fainelli <f.fainelli@xxxxxxxxx>
> ---
>  include/linux/perf_event.h | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 0031f7b4d9ab..592040e2398c 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -1678,8 +1678,15 @@ static struct device_attribute format_attr_##_name = __ATTR_RO(_name)
>  int perf_event_init_cpu(unsigned int cpu);
>  int perf_event_exit_cpu(unsigned int cpu);
>  #else
> -#define perf_event_init_cpu	NULL
> -#define perf_event_exit_cpu	NULL
> +static inline int perf_event_init_cpu(unsigned int cpu)
> +{
> +	return 0;
> +}
> +
> +static inline int perf_event_exit_cpu(unsigned int cpu)
> +{
> +	return 0;
> +}
>  #endif
>  
>  extern void __weak arch_perf_update_userpage(struct perf_event *event,
> -- 
> 2.25.1
>