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

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Message-ID: <55312B38.8050701@fb.com>
Date:	Fri, 17 Apr 2015 09:48:08 -0600
From:	Jens Axboe <axboe@...com>
To:	Dave Jones <davej@...emonkey.org.uk>,
	<torvalds@...uxfoundation.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] Followup single fix for block IO core pull

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

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