linux-kernel - Re: [PATCH v2] m68k: Define NR

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Message-ID: <2ffaf46e-2ed4-49c1-ba0d-82e69b54773a@roeck-us.net>
Date: Tue, 24 Sep 2024 07:09:37 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org,
 David Hildenbrand <david@...hat.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2] m68k: Define NR_CPUS

On 9/24/24 00:47, Geert Uytterhoeven wrote:
> Hi Günter,
> 
> Thanks for your patch!
> 
> On Tue, Sep 24, 2024 at 1:56 AM Guenter Roeck <linux@...ck-us.net> wrote:
>> SPLIT_PTE_PTLOCKS depends on "NR_CPUS >= 4". Unfortunately, that evaluates
>> to true if there is no NR_CPUS configuration option. This results in
>> CONFIG_SPLIT_PTE_PTLOCKS=y for mac_defconfig. This in turn causes the m68k
>> "q800" and "virt" machines to crash in qemu if debugging options are
>> enabled.
>>
>> Making CONFIG_SPLIT_PTE_PTLOCKS dependent on the existence of NR_CPUS
>> does not work since a dependency on the existence of a numeric Kconfig
>> entry always evaluates to false. Example:
>>
>> config HAVE_NO_NR_CPUS
>>         def_bool y
>>         depends on !NR_CPUS
>>
>> After adding this to a Kconfig file, "make defconfig" includes:
>> $ grep NR_CPUS .config
>> CONFIG_NR_CPUS=64
>> CONFIG_HAVE_NO_NR_CPUS=y
>>
>> Define NR_CPUS for m68k instead to solve the problem.
>>
>> Fixes: 394290cba966 ("mm: turn USE_SPLIT_PTE_PTLOCKS / USE_SPLIT_PTE_PTLOCKS into Kconfig options")
>> Cc: David Hildenbrand <david@...hat.com>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
>> Acked-by: David Hildenbrand <david@...hat.com>
> 
> I think it's a bit premature to add David's tag, as v2 is completely
> different from v1.
> 

Ups, sorry, that was an unintentional carryover. Anyway, looks like it
may need v3 anyway.

Guenter