linux-kernel - Re: [PATCH] make CONFIG_EXPERIMENTAL invisible and default

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Message-ID: <CAGXu5jKMDzGMKv7VDFwksCJ_SOvS26-hQFt4xp5VDMoLWGj2pQ@mail.gmail.com>
Date:	Mon, 8 Oct 2012 15:40:57 -0700
From:	Kees Cook <keescook@...omium.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Dave Jones <davej@...hat.com>, Dave Airlie <airlied@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	"David S. Miller" <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] make CONFIG_EXPERIMENTAL invisible and default

On Mon, Oct 8, 2012 at 3:37 PM, Kees Cook <keescook@...omium.org> wrote:
> On Mon, Oct 8, 2012 at 3:29 PM, Paul E. McKenney
> <paulmck@...ux.vnet.ibm.com> wrote:
>> On Mon, Oct 08, 2012 at 03:07:24PM -0700, Kees Cook wrote:
>>> On Sun, Oct 7, 2012 at 6:04 PM, Paul E. McKenney
>>> <paulmck@...ux.vnet.ibm.com> wrote:
>>> > On Sun, Oct 07, 2012 at 04:18:54PM -0400, Dave Jones wrote:
>>> >> On Sun, Oct 07, 2012 at 09:30:29AM -0700, Paul E. McKenney wrote:
>>> >>
>>> >>  > > I think Kconfig is mostly what distro would like to use the thing is
>>> >>  > > the Kconfig text needs to be there upfront when its merged, not two
>>> >>  > > months later, since then it too late for a distro to notice.
>>> >>  > >
>>> >>  > > I'd bet most distros would read the warnings, but in a lot of cases
>>> >>  > > the warning don't exist until its too late.
>>> >>  >
>>> >>  > In the case of CONFIG_RCU_USER_QS you are quite right, the warning
>>> >>  > should have been there from the beginning and was not.  I suppose you
>>> >>  > could argue that the warning was not sufficiently harsh in the case of
>>> >>  > CONFIG_RCU_FAST_NO_HZ, but either way it did get ignored:
>>> >>
>>> >> Maybe if we had a universally agreed upon tag for kconfig, like
>>> >> "distro recommendation: N" that would make things obvious, and also allow
>>> >> those of us unfortunate enough to maintain distro kernels to have something
>>> >> to easily grep for.  This would also catch the case when you eventually (hopefully)
>>> >> flip from an N to a Y.
>>> >>
>>> >> There will likely still be some distros that will decide they know better
>>> >> (and I'm pretty sure eventually I'll find reason to do so myself), but it at least
>>> >> gives the feature maintainer the "I told you so" clause.
>>> >>
>>> >> Something we do quite often for our in-development kernels is enable something
>>> >> that's shiny, new and unproven, and then when we branch for a release, we turn
>>> >> it back off.  It would be great if a lot of this kind of thing could be more automated.
>>> >
>>> > One approach would be to have CONFIG_DISTRO, so that experimental
>>> > features could use "depends on !DISTRO", but also to have multiple
>>> > "BLEEDING" symbols.  For example, given a CONFIG_DISTRO_BLEEDING_HPC
>>> > and CONFIG_DISTRO_BLEEDING_RT, CONFIG_RCU_USER_QS might eventually
>>> > use the following clause:
>>> >
>>> >         depends on !DISTRO || DISTRO_BLEEDING_HPC || DISTRO_BLEEDING_RT
>>> >
>>> > A normal distro would define DISTRO, a distro looking to provide bleeding-edge
>>> > HPC or real-time features would also define DISTRO_BLEEDING_HPC or
>>> > DISTRO_BLEEDING_RT, respectively.
>>> >
>>> > Does that make sense, or am I being overly naive?
>>>
>>> I think we should avoid any global configs that disable things. We'll
>>> just end up in the same place with distros again.
>>
>> So you believe that we should taint the kernel or splat on boot to
>> warn distros off of features that might not be ready for 100 million
>> users?  Or do you have some other approach in mind?
>
> Personally, I think taint+printk seems like the right way to go.

Actually, I think printk is sufficient. I don't want kernel taint to
become the new CONFIG_EXPERIMENTAL. :)

-Kees

-- 
Kees Cook
Chrome OS Security
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