linux-kernel - Re: [PATCH RFC v3 18/21] ACPI: processor: Only call arch_unregister_cpu() if HOTPLUG

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Date: Mon, 18 Dec 2023 12:58:07 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc: linux-pm@...r.kernel.org, loongarch@...ts.linux.dev,
	linux-acpi@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-riscv@...ts.infradead.org, kvmarm@...ts.linux.dev,
	x86@...nel.org, acpica-devel@...ts.linuxfoundation.org,
	linux-csky@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-ia64@...r.kernel.org, linux-parisc@...r.kernel.org,
	Salil Mehta <salil.mehta@...wei.com>,
	Jean-Philippe Brucker <jean-philippe@...aro.org>,
	jianyong.wu@....com, justin.he@....com,
	James Morse <james.morse@....com>
Subject: Re: [PATCH RFC v3 18/21] ACPI: processor: Only call
 arch_unregister_cpu() if HOTPLUG_CPU is selected

On Fri, Dec 15, 2023 at 04:50:09PM +0000, Jonathan Cameron wrote:
> On Wed, 13 Dec 2023 12:50:43 +0000
> Russell King (Oracle) <rmk+kernel@...linux.org.uk> wrote:
> 
> > From: James Morse <james.morse@....com>
> > 
> > The kbuild robot points out that configurations without HOTPLUG_CPU
> > selected can try to build acpi_processor_post_eject() without success
> > as arch_unregister_cpu() is not defined.
> > 
> > Check this explicitly. This will be merged into:
> > | ACPI: Add post_eject to struct acpi_scan_handler for cpu hotplug
> > for any subsequent posting.
> > 
> > Reported-by: kbuild test robot <lkp@...el.com>
> > Signed-off-by: James Morse <james.morse@....com>
> > Tested-by: Miguel Luis <miguel.luis@...cle.com>
> > Tested-by: Vishnu Pajjuri <vishnu@...amperecomputing.com>
> > Tested-by: Jianyong Wu <jianyong.wu@....com>
> > ---
> > This should probably be squashed into an earlier patch.
> 
> Agreed. If not
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>

I'm not convinced that "ACPI: Add post_eject to struct acpi_scan_handler
for cpu hotplug" is the correct commit to squash this into.

As far as acpi_processor.c is concerned, This commit merely renames
acpi_processor_remove() to be acpi_processor_post_eject(). The function
references arch_unregister_cpu() before and after this change, and its
build is dependent on CONFIG_ACPI_HOTPLUG_PRESENT_CPU being defined.

Commit "ACPI: convert acpi_processor_post_eject() to use IS_ENABLED()"
removed the ifdef CONFIG_ACPI_HOTPLUG_PRESENT_CPU surrounding
acpi_processor_post_eject, and that symbol depends on
CONFIG_HOTPLUG_CPU, so I think this commit is also fine.

Commit "ACPI: Check _STA present bit before making CPUs not present"
rewrites the function - the original body gets called
acpi_processor_make_not_present() and a new acpi_processor_post_eject()
is created. At this point, it doesn't reference arch_unregister_cpu().

Commit "ACPI: add support to register CPUs based on the _STA enabled
bit" adds a reference to arch_unregister_cpu() in this new
acpi_processor_post_eject() - so I think this is the correct commit
this change should be merged into.

-- 
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