linux-kernel - Re: [PATCH v4 3/5] acpi_processor: do not mark present at boot but not onlined CPU as onlined

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Date:	Wed, 30 Apr 2014 15:25:51 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	Igor Mammedov <imammedo@...hat.com>
Cc:	linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, x86@...nel.org, bp@...e.de,
	paul.gortmaker@...driver.com, JBeulich@...e.com, prarit@...hat.com,
	drjones@...hat.com, riel@...hat.com, gong.chen@...ux.intel.com,
	andi@...stfloor.org, lenb@...nel.org, rjw@...ysocki.net,
	linux-acpi@...r.kernel.org
Subject: Re: [PATCH v4 3/5] acpi_processor: do not mark present at boot but
 not onlined CPU as onlined

On Mon, 2014-04-14 at 17:11 +0200, Igor Mammedov wrote:
> acpi_processor_add() assumes that present at boot CPUs
> are always onlined, it is not so if a CPU failed to become
> onlined. As result acpi_processor_add() will mark such CPU
> device as onlined in sysfs and following attempts to
> online/offline it using /sys/device/system/cpu/cpuX/online
> attribute will fail.
> 
> Do not poke into device internals in acpi_processor_add()
> and touch "struct device { .offline }" attribute, since
> for CPUs onlined at boot it's set by:
>   topology_init() -> arch_register_cpu() -> register_cpu()
> before ACPI device tree is parsed, and for hotplugged
> CPUs it's set when userspace onlines CPU via sysfs.
> 
> Signed-off-by: Igor Mammedov <imammedo@...hat.com>
> ---
> v2:
>  - fix regression in v1 leading to NULL pointer dereference
>    on CPU unplug, do not remove "pr->dev = dev;"
> ---
>  drivers/acpi/acpi_processor.c |    1 -
>  1 files changed, 0 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> index c29c2c3..42d66f8 100644
> --- a/drivers/acpi/acpi_processor.c
> +++ b/drivers/acpi/acpi_processor.c
> @@ -404,7 +404,6 @@ static int acpi_processor_add(struct acpi_device *device,
>  		goto err;
>  
>  	pr->dev = dev;
> -	dev->offline = pr->flags.need_hotplug_init;

IIRC, this change was necessary to handle the case when maxcpus=X is
specified at boot.  In this case, excessive CPU's dev->offline needs to
be set to 1.  Can you verify this?

Thanks,
-Toshi

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