linux-kernel - Re: [PATCH 1/2] futex: mark futex_detect

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Date:   Mon, 14 Dec 2020 11:22:05 +0100
From:   Marco Elver <elver@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Russell King <linux@...linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Darren Hart <dvhart@...radead.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Elena Reshetova <elena.reshetova@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] futex: mark futex_detect_cmpxchg() as 'noinline'

On Sat, Dec 12, 2020 at 09:01PM +0100, Thomas Gleixner wrote:
> On Sat, Dec 12 2020 at 13:26, Marco Elver wrote:
> > On Thu, Mar 07, 2019 at 10:14AM +0100, Arnd Bergmann wrote:
> >> -static void __init futex_detect_cmpxchg(void)
> >> +static noinline void futex_detect_cmpxchg(void)
> >>  {
> >>  #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
> >>  	u32 curval;
> >
> > What ever happened to this patch?
> 
> It obviously fell through the cracks. 
> 
> > I'm seeing this again with the attached config + next-20201211 (for
> > testing https://bugs.llvm.org/show_bug.cgi?id=48492). Had to apply this
> > patch to build the kernel.
> 
> What really bothers me is to remove the __init from a function which is
> clearly only used during init. And looking deeper it's simply a hack.
> 
> This function is only needed when an architecture has to runtime
> discover whether the CPU supports it or not. ARM has unconditional
> support for this, so the obvious thing to do is the below.
> 
> Thanks,
> 
>         tglx
> ---
>  arch/arm/Kconfig |    1 +
>  1 file changed, 1 insertion(+)
> 
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -86,6 +86,7 @@ config ARM
>  	select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
>  	select HAVE_FUNCTION_GRAPH_TRACER if !THUMB2_KERNEL && !CC_IS_CLANG
>  	select HAVE_FUNCTION_TRACER if !XIP_KERNEL
> +	select HAVE_FUTEX_CMPXCHG if FUTEX
>  	select HAVE_GCC_PLUGINS
>  	select HAVE_HW_BREAKPOINT if PERF_EVENTS && (CPU_V6 || CPU_V6K || CPU_V7)
>  	select HAVE_IDE if PCI || ISA || PCMCIA
> 
> 

This works, too. Thank you!

	Tested-by: Marco Elver <elver@...gle.com>

Thanks,
-- Marco