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

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Message-ID: <20121003174606.GB637@somewhere>
Date:	Wed, 3 Oct 2012 19:46:18 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Kees Cook <keescook@...omium.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 Wed, Oct 03, 2012 at 10:21:42AM -0700, Greg Kroah-Hartman wrote:
> On Wed, Oct 03, 2012 at 09:47:12AM -0700, Paul E. McKenney 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 think that should have been your philosophy for a long time, as they
> turn on everything, and I don't blame them.
> Why would we have included
> it in the kernel tree, unless we wanted people to use the option?

A solution could be to add that option under CONFIG_DEBUG_KERNEL and specify
that it must only be enabled by developers for specific reasons (overhead,
security). CONFIG_PROVE_LOCKING falls into that category, right?

We have CONFIG_RCU_USER_QS that is a specific case. It's an intermediate state
before we implement a true CONFIG_NO_HZ_FULL. But the option is useless on its
own for users. Worse, it introduces a real overhead. OTOH we want it to be upstream
to make the development of full tickless feature more incremental.

Perhaps we should put that under CONFIG_DEBUG_KERNEL.
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