Re: [PATCH v06 3/5] migration/memory: Add hotplug READD_MULTIPLE

[Michael Bringmann <mwb@linux.vnet.ibm.com>]

On 10/16/2018 07:48 PM, Michael Ellerman wrote:
> Michael Bringmann <mwb@linux.vnet.ibm.com> writes:
>> On 10/16/2018 02:57 PM, Tyrel Datwyler wrote:
>>> On 10/15/2018 05:39 PM, Michael Ellerman wrote:
>>>> Michael Bringmann <mwb@linux.vnet.ibm.com> writes:
>>>>> diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c
>>>>> index 2b796da..9c76345 100644
>>>>> --- a/arch/powerpc/platforms/pseries/hotplug-memory.c
>>>>> +++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
>>>>> @@ -541,6 +549,23 @@ static int dlpar_memory_readd_by_index(u32 drc_index)
>>>>>  	return rc;
>>>>>  }
>>>>>
>>>>> +static int dlpar_memory_readd_multiple(void)
>>>>> +{
>>>>> +	struct drmem_lmb *lmb;
>>>>> +	int rc;
>>>>> +
>>>>> +	pr_info("Attempting to update multiple LMBs\n");
>>>>> +
>>>>> +	for_each_drmem_lmb(lmb) {
>>>>> +		if (drmem_lmb_update(lmb)) {
>>>>> +			rc = dlpar_memory_readd_helper(lmb);
>>>>> +			drmem_remove_lmb_update(lmb);
>>>>> +		}
>>>>> +	}
>>>>> +
>>>>> +	return rc;
>>>>> +}
>>>>
>>>> This leaves rc potentially uninitialised.
>>>>
>>>> What should the result be in that case, -EINVAL ?
>>>
>>> On another note if there are multiple LMBs to update the value of rc only reflects the final dlpar_memory_readd_helper() call.
>>
>> Correct.  But that is what happens when we compress common code
>> between two disparate uses i.e. updating memory association after
>> a migration event with no reporting mechanism other than the console
>> log, vs re-adding a single LMB by index for the purposes of DLPAR / drmgr.
>>
>> I could discard the return value from dlpar_memory_readd_helper entirely
>> in this function and just return 0, but in my experience, once errors start
>> to occur in memory dlpar ops, they tend to keep on occurring, so I was
>> returning the last one.  We could also make the code smart enough to
>> capture and return the first/last non-zero return code.  I didn't believe
>> that the frequency of errors for this operation warranted the overhead.
> 
> The actual error value is probably not very relevant.
> 
> But dropping errors entirely is almost always a bad idea.
> 
> So I think you should at least return an error if any error occurred,
> that way at least an error will be returned up to the caller(s).
> 
> Something like:
> 
> 	int rc;
> 
> 	rc = 0;
> 	for_each_drmem_lmb(lmb) {
> 		if (drmem_lmb_update(lmb)) {
> 			rc |= dlpar_memory_readd_helper(lmb);
> 			drmem_remove_lmb_update(lmb);
> 		}
> 	}
> 
> 	if (rc)
> 		return -EIO;

Okay.

> 
> cheers
> 

Thanks.

-- 
Michael W. Bringmann
Linux Technology Center
IBM Corporation
Tie-Line  363-5196
External: (512) 286-5196
Cell:       (512) 466-0650
mwb@linux.vnet.ibm.com