linux-kernel - Re: [PATCH RESEND 1/1] lib/Kconfig: remove DEBUG_PER_CPU_MAPS dependency for CPUMASK

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Message-ID: <cbb6b94e-3b9d-c7b6-a10e-6203a3a8b3f3@oracle.com>
Date:   Tue, 12 Apr 2022 19:34:35 -0700
From:   Libo Chen <libo.chen@...cle.com>
To:     Randy Dunlap <rdunlap@...radead.org>, gregkh@...uxfoundation.org,
        masahiroy@...nel.org, tglx@...utronix.de, peterz@...radead.org,
        mingo@...nel.org, vbabka@...e.cz, akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH RESEND 1/1] lib/Kconfig: remove DEBUG_PER_CPU_MAPS
 dependency for CPUMASK_OFFSTACK



On 4/12/22 19:13, Randy Dunlap wrote:
> Hi,
>
> On 4/12/22 18:35, Libo Chen wrote:
>> Hi Randy,
>>
>> On 4/12/22 17:18, Randy Dunlap wrote:
>>> Hi--
>>>
>>> On 4/12/22 16:15, Libo Chen wrote:
>>>> Forcing CPUMASK_OFFSTACK to be conditoned on DEBUG_PER_CPU_MAPS doesn't
>>>> make a lot of sense nowaday. Even the original patch dating back to 2008,
>>>> aab46da0520a ("cpumask: Add CONFIG_CPUMASK_OFFSTACK") didn't give any
>>>> rationale for such dependency.
>>>>
>>>> Nowhere in the code supports the presumption that DEBUG_PER_CPU_MAPS is
>>>> necessary for CONFIG_CPUMASK_OFFSTACK. Make no mistake, it's good to
>>>> have DEBUG_PER_CPU_MAPS for debugging purpose or precaution, but it's
>>>> simply not a hard requirement for CPUMASK_OFFSTACK. Moreover, x86 Kconfig
>>>> already can set CPUMASK_OFFSTACK=y without DEBUG_PER_CPU_MAPS=y.
>>>> There is no reason other architectures cannot given the fact that they
>>>> have even fewer, if any, arch-specific CONFIG_DEBUG_PER_CPU_MAPS code than
>>>> x86.
>>>>
>>>> Signed-off-by: Libo Chen <libo.chen@...cle.com>
>>>> ---
>>>>    lib/Kconfig | 2 +-
>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/lib/Kconfig b/lib/Kconfig
>>>> index 087e06b4cdfd..7209039dfb59 100644
>>>> --- a/lib/Kconfig
>>>> +++ b/lib/Kconfig
>>>> @@ -511,7 +511,7 @@ config CHECK_SIGNATURE
>>>>        bool
>>>>      config CPUMASK_OFFSTACK
>>>> -    bool "Force CPU masks off stack" if DEBUG_PER_CPU_MAPS
>>> This "if" dependency only controls whether the Kconfig symbol's prompt is
>>> displayed (presented) in kconfig tools. Removing it makes the prompt always
>>> be displayed.
>>>
>>> Any architecture could select (should be able to) CPUMASK_OFFSTACK independently
>>> of DEBUG_PER_CPU_MAPS.
>> Do you mean changing arch/xxxx/Kconfig to select CPUMASK_OFFSTACK under some config xxx? That will work but it requires code changes for each architecture.
>> But if you are talking about setting CONFIG_CPUMASK_OFFSTACK=y without CONFIG_DEBUG_PER_CPU_MAPS directly in config file, I have tried, it doesn't work.
> I'm just talking about the Kconfig change below.  Not talking about whatever else
> it might require per architecture.
>
> But you say you have tried that and it doesn't work. What part of it doesn't work?
> The Kconfig part or some code execution?
oh the Kconfig part. For example, make olddefconfig on a config file 
with CPUMASK_OFFSTACK=y only turns off CPUMASK_OFFSTACK unless I 
explicitly set DEBUG_PER_CPU_MAPS=y

Libo
> I'll test the Kconfig part of it later (in a few hours).
>
>> Libo
>>> Is there another problem here?
>>>
>>>> +    bool "Force CPU masks off stack"
>>>>        help
>>>>          Use dynamic allocation for cpumask_var_t, instead of putting
>>>>          them on the stack.  This is a bit more expensive, but avoids