Re: [GIT PULL] Followup single fix for block IO core pull

Jens Axboe
2015-04-17T15:48:16Z

On 04/17/2015 09:45 AM, Jens Axboe wrote:
> On 04/17/2015 09:41 AM, Dave Jones wrote:
>> On Fri, Apr 17, 2015 at 09:12:01AM -0600, Jens Axboe wrote:
>> > Hi Linus,
>> >
>> > A commit in the previous pull request introduce a regression. So far
>> > only observed on qemu-sparc64, but it's a general bug. Please pull
>> this
>> > single fix to rectify that, thanks.
>>
>> I hit the same bug on two x86 boxes, bare-metal.
>> Reverting the commit Guenter pointed out made them boot again,
>> so definitely not sparc/qemu specific in any way.
>>
>> I suspect the only reason more people didn't see it is that not
>> everyone is running with the mq-by-default config option yet ?
>
> It is puzzling. I ran it on several boxes, both multi queue and not, and
> both single mq queues and multiple. But the code is clearly wrong. So
> yeah, it's not sparc64 specific in any way. My initial thought was that
> this was another issue related to sparse CPU ids, but that's not the
> case. It's a plain bug, unfortunately.

It's the pre morning coffee issue, looks like. All my test boxes end up
having >= map->bits_per_word CPUs, so the test cases never ran into the
round down issue.

--
Jens Axboe