[PATCH v2] powerpc/imc: Dont create debugfs files for cpu-less nodes

[Anju T Sudhakar]

Hi Qian,

On 7/16/19 12:11 AM, Qian Cai wrote:
> On Thu, 2019-07-11 at 14:53 +1000, Michael Ellerman wrote:
>> Hi Maddy,
>>
>> Madhavan Srinivasan <maddy at linux.vnet.ibm.com> writes:
>>> diff --git a/arch/powerpc/platforms/powernv/opal-imc.c
>>> b/arch/powerpc/platforms/powernv/opal-imc.c
>>> index 186109bdd41b..e04b20625cb9 100644
>>> --- a/arch/powerpc/platforms/powernv/opal-imc.c
>>> +++ b/arch/powerpc/platforms/powernv/opal-imc.c
>>> @@ -69,20 +69,20 @@ static void export_imc_mode_and_cmd(struct device_node
>>> *node,
>>>   	if (of_property_read_u32(node, "cb_offset", &cb_offset))
>>>   		cb_offset = IMC_CNTL_BLK_OFFSET;
>>>   
>>> -	for_each_node(nid) {
>>> -		loc = (u64)(pmu_ptr->mem_info[chip].vbase) + cb_offset;
>>> +	while (ptr->vbase != NULL) {
>> This means you'll bail out as soon as you find a node with no vbase, but
>> it's possible we could have a CPU-less node intermingled with other
>> nodes.
>>
>> So I think you want to keep the for loop, but continue if you see a NULL
>> vbase?
> Not sure if this will also takes care of some of those messages during the boot
> on today's linux-next even without this patch.
>
>
> [   18.077780][    T1] debugfs: Directory 'imc' with parent 'powerpc' already
> present!
>
>

This is introduced by a recent commit: c33d442328f55 (debugfs: make 
error message a bit more verbose).

So basically, the debugfs imc_* file is created per node, and is created 
by the first nest unit which is

being registered. For the subsequent nest units, debugfs_create_dir() 
will just return since the imc_* file already

exist.

The commit "c33d442328f55 (debugfs: make error message a bit more 
verbose)", prints

a message if the debugfs file already exists in debugfs_create_dir(). 
That is why we are encountering these

messages now.


This patch (i.e, powerpc/imc: Dont create debugfs files for cpu-less 
nodes) will address the initial issue, i.e

"numa crash while reading imc_* debugfs files for cpu less nodes", and 
will not address these debugfs messages.


But yeah this is a good catch. We can have some checks to avoid these 
debugfs messages.


Hi Michael,

Do we need to have a separate patch to address these debugfs messages, 
or can we address the same

in the next version of this patch itself?


Thanks,

Anju