On Fri, Sep 28, 2018 at 7:53 AM Martin Schwidefsky <schwidefsky@xxxxxxxxxx> wrote: > > On Fri, 28 Sep 2018 07:11:44 -0700 > Andy Lutomirski <luto@xxxxxxxxxxxxxx> 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? > > No, I don't remember. To use a valid kernel pointer with KERNEL_DS and > then test for == 0 (vs -ENOSYS) imho should work. > There may be a much nicer solution. Unless I missed something, only mips and xtensa even have the possibility of cmpxchg being missing. We could just make those arches supply a futex-detecting helper.
