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

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

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.

> 
> -Tyrel

Michael


-- 
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