Re: [PATCH] block/bfq: fix ifdef for CONFIG_BFQ_GROUP_IOSCHED=y

From: Paolo Valente <paolo.valente@linaro.org>
To: "Holger Hoffstätte" <holger@applied-asynchrony.com>
Cc: Jens Axboe <axboe@kernel.dk>,
	Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] block/bfq: fix ifdef for CONFIG_BFQ_GROUP_IOSCHED=y
Date: Mon, 1 Apr 2019 09:34:30 +0200	[thread overview]
Message-ID: <319AA9FF-48BD-40D9-A272-17C6BAFE917F@linaro.org> (raw)
In-Reply-To: <3c87a84f-9fb2-2407-a5a3-723b314d8e58@applied-asynchrony.com>

> Il giorno 29 mar 2019, alle ore 17:44, Holger Hoffstätte <holger@applied-asynchrony.com> ha scritto:
> 
> On 3/29/19 5:15 PM, Jens Axboe wrote:
>>>>> Good catch! I run without group scheduling and therefore didn't notice these
>>>>> stray defines earlier. For 5.1 it should merge cleanly; adding this on top of
>>>>> the pending 5.2 BFQ patches required a small context fixup in hunk #1 due to
>>>>> "block, bfq: do not idle for lowest-weight queues".
>>>> 
>>>> I'm hesitant to apply this, since the group scheduling stuff has obviously never
>>>> been tested.
>>> 
>>> This is simply a regression in 5.1 caused by 73d58118498b - nothing else,
>>> and as such this fix needs to go into 5.1 as well. I'm sure Paolo will agree.
>>> What you so ominously  call "the group scheduling stuff" has been there and
>>> shipping in mainline since day 1 of the BFQ merge, and it works fine in 5.0.
>> If that's the case (I didn't check how far back it went), then yes, it should
>> of course go into 5.1.
> 
> Yay.
> 
>> The ominous nature of my reply I'll chalk up to your interpretation
> 
> Fair enough ;)
> 
> A more interesting question is why upstream uses undefined defines
> for patches. That's a first-rate self-grenade if I've ever seen one,
> and obviously something that is easily missed. Paolo?
> 

Paolo feels a little bit ashamed for this mistake :)

This horrible typo may also be the cause of the crashes recently
reported on this list.  I've just asked to try this fix:
https://lore.kernel.org/linux-block/626EAE58-63C1-4ABA-9040-9D9A61F74A0D@linaro.org/T/

And yes, I agree that this fix should be applied to 5.1.  Thank you
Konstantin for spotting and removing this bomb.

Thanks,
Paolo

> -h