Re: bug in tag handling in blk-mq?

[Jens Axboe]

On 5/9/18 10:57 AM, Mike Galbraith wrote:
> On Wed, 2018-05-09 at 09:18 -0600, Jens Axboe wrote:
>> On 5/8/18 10:11 PM, Mike Galbraith wrote:
>>> On Tue, 2018-05-08 at 19:09 -0600, Jens Axboe wrote:
>>>>
>>>> Alright, I managed to reproduce it. What I think is happening is that
>>>> BFQ is limiting the inflight case to something less than the wake
>>>> batch for sbitmap, which can lead to stalls. I don't have time to test
>>>> this tonight, but perhaps you can give it a go when you are back at it.
>>>> If not, I'll try tomorrow morning.
>>>>
>>>> If this is the issue, I can turn it into a real patch. This is just to
>>>> confirm that the issue goes away with the below.
>>>
>>> Confirmed.  Impressive high speed bug stomping.
>>
>> Well, that's good news. Can I get you to try this patch?
> 
> Sure thing.  The original hang (minus provocation patch) being
> annoyingly non-deterministic, this will (hopefully) take a while.

You can verify with the provocation patch as well first, if you wish.
Just need to hand-apply since it'll conflict with this patch in
bfq. But it's a trivial resolve.

-- 
Jens Axboe