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

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Date:   Thu, 22 Jul 2021 13:05:59 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Marco Elver <elver@...gle.com>, 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 09:01:34PM +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
> 
> 

Hi Thomas,

Did this ever get sent along as a formal patch? I just ran into another
issue that seems to be similar to the one Arnd sent the initial patch in
this thread for and it is resolved by this change.

Cheers,
Nathan