Re: [PATCH] posix-timers: omit posix_cpu_timers_init_group when CONFIG_POSIX_TIMERS is disabled

[Thomas Gleixner <tglx@linutronix.de>]

On Sat, Jun 07 2025 at 19:41, Liya Huang wrote:
>     When POSIX timers are disabled (CONFIG_POSIX_TIMERS=n), the helper
>     function posix_cpu_timers_init_group() is effectively a no-op—but it
>     still consumes valuable code space. To avoid generating an empty stub,
>     we should conditionally compile this function out entirely when POSIX
>     timers support is turned off.

I have no idea what you are trying to say here. See below.

> This logic was originally introduced in commit b18b6a9cef7f ("timers:
>     Omit POSIX timer stuff from task_struct when disabled"), but was
>     dropped in commit 244d49e30653 ("posix-cpu-timers: Move state tracking
>      to struct posix_cputimers")

Can you please format your change logs properly as everybody else
does? These indents provide zero value.

> ---
> Signed-off-by: Liya Huang <1425075683@qq.com>
> ---
>  kernel/fork.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 168681fc4b25a9fddcb90ce155c027551455f4ee..9632e863c17b44424fadc40b2445034ec5cd20d6 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1883,6 +1883,7 @@ void __cleanup_sighand(struct sighand_struct *sighand)
>  	}
>  }
>  
> +#ifdef CONFIG_POSIX_TIMERS
>  /*
>   * Initialize POSIX timer handling for a thread group.
>   */
> @@ -1894,6 +1895,9 @@ static void posix_cpu_timers_init_group(struct signal_struct *sig)
>  	cpu_limit = READ_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
>  	posix_cputimers_group_init(pct, cpu_limit);
>  }
> +#else
> +static inline void posix_cpu_timers_init_group(struct signal_struct *sig) { }
> +#endif

If CONFIG_POSIX_TIMERS=n then posix_cputimers_group_init() is an empty
inline function and the compiler optimizes posix_cpu_timers_init_group()
away completely. If it does not, then the compiler wants to be fixed.

And no, we are not adding ugly ifdeffery just because.

Thanks,

        tglx