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

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Message-ID: <20121003200314.GR2527@linux.vnet.ibm.com>
Date:	Wed, 3 Oct 2012 13:03:14 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Kees Cook <keescook@...omium.org>
Cc:	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>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH] make CONFIG_EXPERIMENTAL invisible and default

On Wed, Oct 03, 2012 at 11:43:32AM -0700, Kees Cook wrote:
> On Wed, Oct 3, 2012 at 9:47 AM, Paul E. McKenney
> <paulmck@...ux.vnet.ibm.com> wrote:
> > On Wed, Oct 03, 2012 at 09:17:02AM -0700, Greg Kroah-Hartman wrote:
> >> On Wed, Oct 03, 2012 at 06:25:38AM -0700, Paul E. McKenney wrote:
> >> > On Tue, Oct 02, 2012 at 12:50:42PM -0700, Kees Cook wrote:
> >> > > This config item has not carried much meaning for a while now and is
> >> > > almost always enabled by default. As agreed during the Linux kernel
> >> > > summit, it should be removed. As a first step, remove it from being
> >> > > listed, and default it to on. Once it has been removed from all
> >> > > subsystem Kconfigs, it will be dropped entirely.
> >> > >
> >> > > CC: Greg KH <gregkh@...uxfoundation.org>
> >> > > CC: "Eric W. Biederman" <ebiederm@...ssion.com>
> >> > > CC: Serge Hallyn <serge.hallyn@...onical.com>
> >> > > CC: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> >> > > CC: Andrew Morton <akpm@...ux-foundation.org>
> >> > > CC: Frederic Weisbecker <fweisbec@...il.com>
> >> > > Signed-off-by: Kees Cook <keescook@...omium.org>
> >> > > ---
> >> > >
> >> > > This is the first of a series of 202 patches removing EXPERIMENTAL from
> >> > > all the Kconfigs in the tree. Should I send them all to lkml (with all
> >> > > the associated CCs), or do people want to cherry-pick changes from my
> >> > > tree? I don't want to needlessly flood the list.
> >> > >
> >> > > http://git.kernel.org/?p=linux/kernel/git/kees/linux.git;a=shortlog;h=refs/heads/experimental
> >> > >
> >> > > I figure this patch can stand alone to at least make EXPERIMENTAL go
> >> > > away from the menus, and give us a taste of what the removal would do
> >> > > to builds.
> >> >
> >> > OK, I will bite...  How should I flag an option that is initially only
> >> > intended for those willing to take some level of risk?
> >>
> >> In the text say "You really don't want to enable this option, use at
> >> your own risk!"  Or something like that :)
> >
> > OK, so the only real hope for experimental features is to refrain from
> > creating a config option for them, so that people wishing to use them
> > must modify the code?  Or is the philosophy that we keep things out of
> > tree until we are comfortable with distros turning them on?
> 
> I would expect a simple addition of "this is dangerous/buggy" to the
> description and "default n" is likely the way to go for that kind of
> thing. I think the history of CONFIG_EXPERIMENTAL has proven there
> isn't a sensible way to create a global flag for this kind of thing.
> To paraphrase Serge: my experimental options are not your experimental
> options.

That has not proven sufficient for me in the past, RCU_FAST_NO_HZ
being a case in point.

> For example, some of the things that already had the experimental
> config removed, they left the "(EXPERIMENTAL)" in their config title.

Or I could just make it splat at boot time.  ;-)

							Thanx, Paul

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