linux-kernel - Re: [PATCH 2/5] alpha: Modify the definition logic of WEAK_PER

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Message-ID: <496a782f-25f8-44c5-88dd-d2c56a585898@linux.dev>
Date: Thu, 12 Jun 2025 20:06:25 +0800
From: Hao Ge <hao.ge@...ux.dev>
To: Heiko Carstens <hca@...ux.ibm.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Suren Baghdasaryan <surenb@...gle.com>
Cc: David Hildenbrand <david@...hat.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka
 <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
 Richard Henderson <richard.henderson@...aro.org>,
 Matt Turner <mattst88@...il.com>, Dennis Zhou <dennis@...nel.org>,
 Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>,
 Vasily Gorbik <gor@...ux.ibm.com>, Alexander Gordeev
 <agordeev@...ux.ibm.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>,
 Kent Overstreet <kent.overstreet@...ux.dev>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, linux-alpha@...r.kernel.org,
 linux-s390@...r.kernel.org, Hao Ge <gehao@...inos.cn>
Subject: Re: [PATCH 2/5] alpha: Modify the definition logic of WEAK_PER_CPU

On 2025/6/12 19:22, Heiko Carstens wrote:
> On Thu, Jun 12, 2025 at 04:27:27PM +0800, Hao Ge wrote:
>> From: Hao Ge <gehao@...inos.cn>
>>
>> As stated in the first patch of this patch series,
>> we make ARCH_NEEDS_WEAK_PER_CPU a Kconfig option,
>> and replace all instances of ARCH_NEEDS_WEAK_PER_CPU
>> in the kernel code with MODULE_NEEDS_WEAK_PER_CPU,
>> gated by #ifdef CONFIG_ARCH_NEEDS_WEAK_PER_CPU.
>>
>> We'll make corresponding changes for the alpha
>> architecture.
>>
>> Suggested-by: Suren Baghdasaryan <surenb@...gle.com>
>> Signed-off-by: Hao Ge <gehao@...inos.cn>
>> ---
>>   arch/alpha/Kconfig              | 1 +
>>   arch/alpha/include/asm/percpu.h | 4 ++--
>>   2 files changed, 3 insertions(+), 2 deletions(-)
> ...
>
>> +	select ARCH_NEEDS_WEAK_PER_CPU
>>   	select ARCH_NO_PREEMPT
>>   	select ARCH_NO_SG_CHAIN
>>   	select ARCH_USE_CMPXCHG_LOCKREF
>> diff --git a/arch/alpha/include/asm/percpu.h b/arch/alpha/include/asm/percpu.h
>> index 6923249f2d49..5d8b75ec3bf2 100644
>> --- a/arch/alpha/include/asm/percpu.h
>> +++ b/arch/alpha/include/asm/percpu.h
>> @@ -10,8 +10,8 @@
>>    *
>>    * Always use weak definitions for percpu variables in modules.
>>    */
>> -#if defined(MODULE) && defined(CONFIG_SMP)
>> -#define ARCH_NEEDS_WEAK_PER_CPU
>> +#if defined(MODULE) && defined(CONFIG_SMP) && defined(CONFIG_ARCH_NEEDS_WEAK_PER_CPU)
>> +#define MODULE_NEEDS_WEAK_PER_CPU

Hi Heiko

Thank you for taking the time to review these patches.

> CONFIG_ARCH_NEEDS_WEAK_PER_CPU is always set with the above select.
> So there is no point in adding this to the check.
Yes, that's exactly the case.
> Furthermore this removes ARCH_NEEDS_WEAK_PER_CPU and defines
> MODULE_NEEDS_WEAK_PER_CPU while the common code conversion happens
> only with patch 4. Or in other words: if patches are split like this
> things break.
>
> Same is true for patch 3. Just merging patches 2-4 would be the
> easiest solution to this problem.

I think this should be CC'd to the stable branch.

I'm wondering if these need to be integrated into a single patch.

I'm not sure. What do you think?

Hi Andrew and Suren

How do you see this? Any suggestions?

Thanks
Best Regards
Hao