linux-kernel - Re: [PATCH v3] acpi: Fix CPU hot removal problem

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Date:	Wed, 14 Sep 2011 08:14:04 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	"canquan.shen" <shencanquan@...wei.com>
Cc:	len.brown@...el.com,
	"shemminger@...tta.com" <shemminger@...tta.com>,
	"yakui.zhao@...el.com" <yakui.zhao@...el.com>,
	"xiaowei.yang@...wei.com" <xiaowei.yang@...wei.com>,
	hanweidong <hanweidong@...wei.com>, linqiangmin@...wei.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v3] acpi: Fix CPU hot removal problem

On Tue, Sep 13, 2011 at 8:18 PM, canquan.shen <shencanquan@...wei.com> wrote:
> We run linux as a guest in Xen environment. When we used the xen tools
> (xm vcpu-set <n>) to hot add and remove vcpu to and from the guest, we
> encountered the failure on vcpu removal. We found the reason is that it
> didn't go to really remove cpu in the cpu removal code path.
>
> This patch adds acpi_bus_trim in acpi_process_hotplug_notify to fix this
> issue. With this patch, it works fine for us.
>
> Signed-off-by: Shen canquan <shencanquan@...wei.com>
> ---
>  drivers/acpi/processor_driver.c |    7 +++++++
>  1 files changed, 7 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/acpi/processor_driver.c
> b/drivers/acpi/processor_driver.c
> index a4e0f1b..0856ef8 100644
> --- a/drivers/acpi/processor_driver.c
> +++ b/drivers/acpi/processor_driver.c
> @@ -677,6 +677,13 @@ static void acpi_processor_hotplug_notify(acpi_handle
> handle,
>                                    "Driver data is NULL, dropping EJECT\n");
>                        return;
>                }
> +               ACPI_DEBUG_PRINT((ACPI_DB_INFO,
> +                       "Hot-removing processor device %s\n",
> +                       dev_name(&device->dev)));
> +               if (acpi_bus_trim(device, 1)) {
> +                       printk(KERN_ERR "ACPI: Removing device failed!\n");

We can do better than that.  Nobody ever looks at ACPI_DEBUG_PRINT info.

    u32 id;
    ...
    id = pr->id;
    if (acpi_bus_trim(device, 1))
        printk(KERN_ERR PREFIX "Failed to remove CPU %d\n", id);

(No "return" needed here.  In fact, the "return" at the bottom of
acpi_processor_hotplug_notify() is also superfluous.  You could remove
it at the same time.)
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