Re: [PATCH 3/6] M68K: cpuinfo: Fix a warning for CONFIG_CPUMASK_OFFSTACK

From: WANG Xuerui
Date: Tue Jul 12 2022 - 06:15:55 EST

Hi Geert and Huacai,

On 2022/7/12 17:13, Geert Uytterhoeven wrote:
Hi Huacai,

On Tue, Jul 12, 2022 at 11:08 AM Huacai Chen <chenhuacai@xxxxxxxxx> wrote:
On Tue, Jul 12, 2022 at 5:01 PM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
On Tue, Jul 12, 2022 at 10:53 AM Huacai Chen <chenhuacai@xxxxxxxxx> wrote:
On Tue, Jul 12, 2022 at 4:33 PM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
On Tue, Jul 12, 2022 at 9:53 AM Huacai Chen <chenhuacai@xxxxxxxxxxx> wrote:
DEBUG_PER_CPU_MAPS depends on SMP, which is not supported on m68k,
and thus cannot be enabled.
This patch is derived from MIPS and LoongArch, I search all
architectures and change those that look the same as MIPS and
And the warning message below is also a copy-paste from LoongArch, sorry.

Since M68K doesn't support SMP, then this patch seems to make no
difference, but does it make sense to keep consistency across all
Yes, having consistency is good. But that should be mentioned in the
patch description, instead of a scary warning CCed to stable ;-)

BTW, you probably want to update the other copy of c_start() in
arch/m68k/kernel/setup_mm.c, too.
For no-SMP architectures, it seems c_start() in
arch/m68k/kernel/setup_mm.c is more reasonable (just use 1, neither
NR_CPUS, nor nr_cpu_ids)?
The advantage of using nr_cpu_ids() is that this is one place less
to update when adding SMP support later...

Hmm, so I've been watching m68k development lately (although not as closely as I'd like to, due to lack of vintage hardware at hand), given the current amazing  momentum all the hobbyists/developers have been contributing to, SMP is well within reach...

But judging from the intent of this patch series (fixing WARNs on certain configs), and that the triggering condition is currently impossible on m68k (and other non-SMP) platforms, I think cleanups for such arches could come as a separate patch series later. I think the m68k refactoring is reasonable after all, due to my observation above, but for the other non-SMP arches we may want to wait for the respective maintainers' opinions.