[PATCH v3] acpi: Fix CPU hot removal problem

[PATCH v3] acpi: Fix CPU hot removal problem

[canquan.shen]

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@huawei.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");
+			return;
+		}
  		break;
  	default:
  		ACPI_DEBUG_PRINT((ACPI_DB_INFO,
-- 
1.7.6.0

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

[Bjorn Helgaas]

On Tue, Sep 13, 2011 at 8:18 PM, canquan.shen <shencanquan@huawei.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@huawei.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.)

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

[canquan.shen]

On 2011/9/14 22:14, Bjorn Helgaas wrote:
> On Tue, Sep 13, 2011 at 8:18 PM, canquan.shen<shencanquan@huawei.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@huawei.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.)
>
> .
>

Thanks for your suggestion. I will modify it and resend the patch.

--
Canquan.shen