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Date:   Thu, 19 Apr 2018 17:57:25 +0200
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Thomas Backlund <tmb@mageia.org>
Cc:     Jan Kara <jack@suse.cz>,
        Sasha Levin <Alexander.Levin@microsoft.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Petr Mladek <pmladek@suse.com>,
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        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Cong Wang <xiyou.wangcong@gmail.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@kernel.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Peter Zijlstra <peterz@infradead.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        Byungchul Park <byungchul.park@lge.com>,
        Tejun Heo <tj@kernel.org>, Pavel Machek <pavel@ucw.cz>
Subject: Re: [PATCH AUTOSEL for 4.14 015/161] printk: Add console owner and
 waiter logic to load balance console writes
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On Thu, Apr 19, 2018 at 06:16:26PM +0300, Thomas Backlund wrote:
> Den 19.04.2018 kl. 17:22, skrev Greg KH:
> > On Thu, Apr 19, 2018 at 04:05:45PM +0200, Jan Kara wrote:
> > > On Thu 19-04-18 15:59:43, Greg KH wrote:
> > > > 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@microsoft.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.
> > > 
> > > Sure, that's understood. So this was just misunderstanding. Sasha's
> > > original comment really sounded like "bug compatibility" with current
> > > master is desirable and that made me go "Are you serious?" as well...
> > 
> > As I said before in this thread, yes, sometimes I do this on purpose.
> > 
> 
> And I guess this is the one that gets people the feeling that
> "stable is not as stable as it used to be" ...

It's always been this way, it's just that no one noticed :)

> > As an specific example, see a recent bluetooth patch that caused a
> > regression on some chromebook devices.  The chromeos developers
> > rightfully complainied, and I left the commit in there to provide the
> > needed "leverage" on the upstream developers to fix this properly.
> > Otherwise if I had reverted the stable patch, when people move to a
> > newer kernel version, things break, and no one remembers why.
> 
> I do understand what you are trying to do...
> 
> But from my distro hat on I have to treat things differently (and I dont
> think I'm alone doing it this way...)
> 
> Known breakages gets reverted even before it hits QA, so endusers wont see
> the issue at all...
> 
> So the only ones to see the issue are those building with latest upstream
> without own patches applied...
> 
> > 
> > I also wrote a long response as to _why_ I do this, and even though it
> > does happen, why it still is worth taking the stable updates.  Please
> > see the archives for the full details.  I don't want to duplicate this
> > again here.
> 
> And we do use latest stable (with some delay as I dont want to overload QA &
> endusers with a new kernel every week :))

You need to automate your QA :)

> We just revert known broken (or add known fixes) before releasing them to
> our users

That's great, and is what you should be doing, nothing wrong there.

thanks,

greg k-h