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: <20180419135943.GC16862@kroah.com>
Date:   Thu, 19 Apr 2018 15:59:43 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     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

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 :)

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.

thanks,

greg k-h