Re: Another (ESP?) scsi blk-mq problem on sparc64

[Jens Axboe <axboe@kernel.dk>]

On 11/24/2014 10:31 AM, Paul E. McKenney wrote:
> On Mon, Nov 24, 2014 at 10:16:15AM -0700, Jens Axboe wrote:
>> On 11/24/2014 09:22 AM, Paul E. McKenney wrote:
>>> On Mon, Nov 24, 2014 at 08:35:46AM -0700, Jens Axboe wrote:
>>>> On 11/24/2014 01:21 AM, Christoph Hellwig wrote:
>>>>> On Fri, Nov 21, 2014 at 02:56:00PM -0500, David Miller wrote:
>>>>>> I would suggest looking into the possibility that we allocate the memory
>>>>>> using the count of valid cpus, rather than the largest cpu number.
>>>>>>
>>>>>> That's a common error that runs into problems with discontiguous
>>>>>> cpu numbering like Sparc sometimes has.
>>>>>
>>>>> Yes, that does look like the case.  Do you have a good trick on how
>>>>> to allocate a map for the highest possible cpu number without first
>>>>> iterating the cpu map?  I couldn't find something that looks like a
>>>>> highest_possible_cpu() helper.
>>>>
>>>> Honestly I think that num_posible_cpus() should return the max of
>>>> number of CPUs (weigt), and the highest numbered CPU. It's a pain in
>>>> the butt to handle this otherwise.
>>>
>>> Hear, hear!!!  That would make my life easier, and would make this sort
>>> of problem much less likely to occur!
>>
>> How about this one?
>
> Works for me!

Thanks! I'll add an appropriate comment and send it out for review.

> (Just for the record, as far as I know, this doesn't matter for RCU,
> which already uses nr_cpu_ids.)

Was that done after hitting something like this?

Meelis, can you check if it fixes your issue?


-- 
Jens Axboe