linux-kernel - Re: [PATCH AUTOSEL for 4.14 015/161] printk: Add console owner and waiter logic to load balance console writes

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Message-ID: <6425991f-7d7f-b1f9-ba37-3212a01ad6cf@mageia.org>
Date:   Thu, 19 Apr 2018 18:04:26 +0300
From:   Thomas Backlund <tmb@...eia.org>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Thomas Backlund <tmb@...eia.org>
CC:     Sasha Levin <Alexander.Levin@...rosoft.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Petr Mladek <pmladek@...e.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Peter Zijlstra <peterz@...radead.org>, Jan Kara <jack@...e.cz>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Byungchul Park <byungchul.park@....com>,
        Tejun Heo <tj@...nel.org>, Pavel Machek <pavel@....cz>
Subject: Re: [PATCH AUTOSEL for 4.14 015/161] printk: Add console owner and
 waiter logic to load balance console writes

Den 19.04.2018 kl. 16:59, skrev Greg KH:
> On Thu, Apr 19, 2018 at 02:41:33PM +0300, Thomas Backlund wrote:
>> Den 16-04-2018 kl. 19:19, skrev Sasha Levin:
>>> On Mon, Apr 16, 2018 at 12:12:24PM -0400, Steven Rostedt wrote:
>>>> On Mon, 16 Apr 2018 16:02:03 +0000
>>>> Sasha Levin <Alexander.Levin@...rosoft.com> wrote:
>>>>
>>>>> One of the things Greg is pushing strongly for is "bug compatibility":
>>>>> we want the kernel to behave the same way between mainline and stable.
>>>>> If the code is broken, it should be broken in the same way.
>>>>
>>>> Wait! What does that mean? What's the purpose of stable if it is as
>>>> broken as mainline?
>>>
>>> This just means that if there is a fix that went in mainline, and the
>>> fix is broken somehow, we'd rather take the broken fix than not.
>>>
>>> In this scenario, *something* will be broken, it's just a matter of
>>> what. We'd rather have the same thing broken between mainline and
>>> stable.
>>>
>>
>> Yeah, but _intentionally_ breaking existing setups to stay "bug compatible"
>> _is_ a _regression_ you _really_ _dont_ want in a stable
>> supported distro. Because end-users dont care about upstream breaking
>> stuff... its the distro that takes the heat for that...
>>
>> Something "already broken" is not a regression...
>>
>> As distro maintainer that means one now have to review _every_ patch that
>> carries "AUTOSEL", follow all the mail threads that comes up about it, then
>> track if it landed in -stable queue, and read every response and possible
>> objection to all patches in the -stable queue a second time around... then
>> check if it still got included in final stable point relase and then either
>> revert them in distro kernel or go track down all the follow-up fixes
>> needed...
>>
>> Just to avoid being "bug compatible with master"
> 
> I've done this "bug compatible" "breakage" more than the AUTOSEL stuff
> has in the past, so you had better also be reviewing all of my normal
> commits as well :)
> 

Yeah, I do... and same goes there ... if there is a known issue, then 
same procedure... Either revert, or try to track down fixes...


> Anyway, we are trying not to do this, but it does, and will,
> occasionally happen.  Look, we just did that for one platform for
> 4.9.94!  And the key to all of this is good testing, which we are now
> doing, and hopefully you are also doing as well.

Yeah, but having to test stuff with known breakages is no fun, so we try 
to avoid that

--
Thomas