Re: [PATCH v6] mm/percpu: Conditionally define _shared_alloc_tag via CONFIG_ARCH_MODULE_NEEDS_WEAK_PER_CPU

[Mike Rapoport <rppt@kernel.org>]

On Wed, Jun 18, 2025 at 09:58:09AM +0800, Hao Ge wrote:
> From: Hao Ge <gehao@kylinos.cn>
> 
> Recently discovered this entry while checking kallsyms on ARM64:
> ffff800083e509c0 D _shared_alloc_tag
> 
> If ARCH_NEEDS_WEAK_PER_CPU is not defined(it is only defined for
> s390 and alpha architectures), there's no need to statically define
> the percpu variable _shared_alloc_tag.
> 
> Therefore, we need to implement isolation for this purpose.
> 
> When building the core kernel code for s390 or alpha architectures,
> ARCH_NEEDS_WEAK_PER_CPU remains undefined (as it is gated
> by #if defined(MODULE)). However, when building modules for these
> architectures, the macro is explicitly defined.
> 
> Therefore, we remove all instances of ARCH_NEEDS_WEAK_PER_CPU from
> the code and introduced CONFIG_ARCH_MODULE_NEEDS_WEAK_PER_CPU to
> replace the relevant logic. We can now conditionally define the perpcu
> variable _shared_alloc_tag based on CONFIG_ARCH_MODULE_NEEDS_WEAK_PER_CPU.
> This allows architectures (such as s390/alpha) that require weak
> definitions for percpu variables in modules to include the definition,
> while others can omit it via compile-time exclusion.
> 
> Suggested-by: Suren Baghdasaryan <surenb@google.com>
> Acked-by: Alexander Gordeev <agordeev@linux.ibm.com> # s390
> Signed-off-by: Hao Ge <gehao@kylinos.cn>

Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

-- 
Sincerely yours,
Mike.