[PATCH v2] acpi: Fix CPU hot removal problem

[PATCH v2] acpi: Fix CPU hot removal problem

[canquan.shen]

We run Linux as a guest in Xen environment. When used 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: Canquan Shen <shencanquan@huawei.com>
---
  drivers/acpi/processor_driver.c |    5 +++++
  1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/drivers/acpi/processor_driver.c 
b/drivers/acpi/processor_driver.c
index a1c564f..114592f 100644
--- a/drivers/acpi/processor_driver.c
+++ b/drivers/acpi/processor_driver.c
@@ -678,7 +678,11 @@ static void 
acpi_processor_hotplug_notify(acpi_handle handle,
              return;
          }

+        if (acpi_bus_trim(device, 1)) {
+            printk(KERN_ERR PREFIX
+                    "Removing device failed\n");
+            return;
+        }
          break;
      default:
          ACPI_DEBUG_PRINT((ACPI_DB_INFO,
-- 
1.7.6

Re: [PATCH v2] acpi: Fix CPU hot removal problem

[canquan.shen]

On 2011/9/8 10:39, canquan.shen wrote:
> We run Linux as a guest in Xen environment. When used 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: Canquan Shen <shencanquan@huawei.com>
> ---
> drivers/acpi/processor_driver.c | 5 +++++
> 1 files changed, 5 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/acpi/processor_driver.c
> b/drivers/acpi/processor_driver.c
> index a1c564f..114592f 100644
> --- a/drivers/acpi/processor_driver.c
> +++ b/drivers/acpi/processor_driver.c
> @@ -678,7 +678,11 @@ static void
> acpi_processor_hotplug_notify(acpi_handle handle,
> return;
> }
>
> + if (acpi_bus_trim(device, 1)) {
> + printk(KERN_ERR PREFIX
> + "Removing device failed\n");
> + return;
> + }
> break;
> default:
> ACPI_DEBUG_PRINT((ACPI_DB_INFO,

Hi Len,
     I just see your email in linux-kernel maillist and known that your 
kernel.org email is kaput, so I resend this email to your intel email 
address.

Thanks,
- Canquan Shen

Re: [PATCH v2] acpi: Fix CPU hot removal problem

[Bjorn Helgaas]

On Mon, Sep 12, 2011 at 11:58 PM, canquan.shen <shencanquan@huawei.com> wrote:
> On 2011/9/8 10:39, canquan.shen wrote:
>>
>> We run Linux as a guest in Xen environment. When used 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: Canquan Shen <shencanquan@huawei.com>
>> ---
>> drivers/acpi/processor_driver.c | 5 +++++
>> 1 files changed, 5 insertions(+), 0 deletions(-)
>>
>> diff --git a/drivers/acpi/processor_driver.c
>> b/drivers/acpi/processor_driver.c
>> index a1c564f..114592f 100644
>> --- a/drivers/acpi/processor_driver.c
>> +++ b/drivers/acpi/processor_driver.c
>> @@ -678,7 +678,11 @@ static void
>> acpi_processor_hotplug_notify(acpi_handle handle,
>> return;
>> }
>>
>> + if (acpi_bus_trim(device, 1)) {
>> + printk(KERN_ERR PREFIX
>> + "Removing device failed\n");
>> + return;
>> + }
>> break;
>> default:
>> ACPI_DEBUG_PRINT((ACPI_DB_INFO,

I think this patch is OK.  One nit is that kernel printks should never
be constant strings.  There's almost always more information that's
useful in debugging.  This error should at least tell us which driver
is involved, and preferably which specific device (though we have to
be careful in case the device struct is freed by acpi_bus_trim()).

Bjorn