On Mon, Oct 8, 2012 at 3:59 PM, Paul E. McKenney <paul...@linux.vnet.ibm.com> wrote: > On Mon, Oct 08, 2012 at 03:40:57PM -0700, Kees Cook wrote: >> On Mon, Oct 8, 2012 at 3:37 PM, Kees Cook <keesc...@chromium.org> wrote: >> > On Mon, Oct 8, 2012 at 3:29 PM, Paul E. McKenney >> > <paul...@linux.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 >> >>> <paul...@linux.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. :) > > OK, I'll bite... > > Why would kernel taint be more likely to become the new CONFIG_EXPERIMENTAL > than printk() would?
I was imagining the case where distros were still turning lots of stuff on, and they wanted a genuinely experimental thing anyway, then they'd end up with all their kernels tainted. A printk is easier to "live with", where as taint wouldn't be, I think. -Kees -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
