On 2/19/19 2:03 PM, Tyrel Datwyler wrote:
> On 02/19/2019 07:46 AM, Michael Bringmann wrote:
>> powerpc/pseries: Fix dn reference error in dlpar_cpu_remove_by_index()
>>
>> A reference to the device node of the CPU to be removed is released
>> upon successful removal of the associated CPU device. If the call
>> to remove the CPU device fails, dlpar_cpu_remove_by_index() still
>> frees the reference and this leads to miscomparisons and/or
>> addressing errors later on.
>>
>> This problem may be observed when trying to DLPAR 'hot-remove' a CPU
>> from a system that has only a single CPU. The operation will fail
>> because there is no other CPU to which the kernel operations may be
>> migrated, but the refcount will still be decremented.
>>
>> Signed-off-by: Michael Bringmann
>>
>>
>> diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c
>> b/arch/powerpc/platforms/pseries/hotplug-cpu.c
>> index 97feb6e..9537bb9 100644
>> --- a/arch/powerpc/platforms/pseries/hotplug-cpu.c
>> +++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c
>> @@ -635,7 +635,8 @@ static int dlpar_cpu_remove_by_index(u32 drc_index)
>> }
>>
>> rc = dlpar_cpu_remove(dn, drc_index);
>> -of_node_put(dn);
>> +if (!rc)
>> +of_node_put(dn);
>> return rc;
>> }
>>
>
> NACK!
>
> The logic here is wrong. Here is the full function.
>
> static int dlpar_cpu_remove_by_index(u32 drc_index)
> {
> struct device_node *dn;
> int rc;
>
> dn = cpu_drc_index_to_dn(drc_index);
> if (!dn) {
> pr_warn("Cannot find CPU (drc index %x) to remove\n",
> drc_index);
> return -ENODEV;
> }
>
> rc = dlpar_cpu_remove(dn, drc_index);
> of_node_put(dn);
> return rc;
> }
>
> The call to cpu_drc_index_to_dn() returns a device_node with the reference
> count
> incremented. So, regardless of the success or failure of the call to
> dlpar_cpu_remove() you need to release that reference.
>
> If there is a reference counting issue it is somewhere else.
Okay. Withdrawn while we look some more.
> -Tyrel
--
Michael W. Bringmann
Linux Technology Center
IBM Corporation
Tie-Line 363-5196
External: (512) 286-5196
Cell: (512) 466-0650
m...@linux.vnet.ibm.com
