On Fri, 28 Sep 2018, Andy Lutomirski wrote: > > On Sep 28, 2018, at 1:42 AM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > > > >> On Fri, 28 Sep 2018, Martin Schwidefsky wrote: > >> On Fri, 28 Sep 2018 09:12:10 +0200 > >> Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: > >>> I don't know if that has happened, and whether it would work on s390 now. > >> > >> commit 03b8c7b623c80af264c4c8d6111e5c6289933666 > >> Author: Heiko Carstens <heiko.carstens@xxxxxxxxxx> > >> Date: Sun Mar 2 13:09:47 2014 +0100 > >> > >> futex: Allow architectures to skip futex_atomic_cmpxchg_inatomic() test > >> > >> If an architecture has futex_atomic_cmpxchg_inatomic() implemented and there > >> is no runtime check necessary, allow to skip the test within futex_init(). > >> > >> This allows to get rid of some code which would always give the same result, > >> and also allows the compiler to optimize a couple of if statements away. > >> > >> Signed-off-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx> > >> Cc: Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx> > >> Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> > >> Link: http://lkml.kernel.org/r/20140302120947.GA3641@osiris > >> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > >> > >> > >> Heiko created the CONFIG_HAVE_FUTEX_CMPXCHG to get around this issue. > >> We just skip the runtime check as well as arc, m68k and sh. Not sure > >> about xtensa, the set it config option only for !MMU. > > > > Duh. grep would have told me. -ENOTENOUGHCOFFEE > > > > > There’s another way to skin this cat: keep KERNEL_DS but pass a valid > pointer. I don’t suppose you remember why you didn’t do that? IIRC, there was an issue with extra checks in some architectures when you handed in a kernel address spitting warnings or such. That's probably gone by now, but I can't tell for sure. At least the requirement to do runtime detection for x86 is gone. Don't know if any other architecture still has it. Thanks, tglx
