Re: [PATCH] locking/atomic: sh: Use generic_cmpxchg_local for arch_cmpxchg_local()

[John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>]

On Wed, 2023-10-25 at 11:30 +0100, Mark Rutland wrote:
> On Wed, Oct 25, 2023 at 08:42:55AM +0900, Masami Hiramatsu wrote:
> > On Tue, 24 Oct 2023 16:08:12 +0100
> > Mark Rutland <mark.rutland@arm.com> wrote:
> > 
> > > On Tue, Oct 24, 2023 at 11:52:54PM +0900, Masami Hiramatsu (Google) wrote:
> > > > From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > > > 
> > > > Use generic_cmpxchg_local() for arch_cmpxchg_local() implementation
> > > > in SH architecture because it does not implement arch_cmpxchg_local().
> > > 
> > > I do not think this is correct.
> > > 
> > > The implementation in <asm-generic/cmpxchg-local.h> is UP-only (and it only
> > > disables interrupts), whereas arch/sh can be built SMP. We should probably add
> > > some guards into <asm-generic/cmpxchg-local.h> for that as we have in
> > > <asm-generic/cmpxchg.h>.
> > 
> > Isn't cmpxchg_local for the data which only needs to ensure to do cmpxchg
> > on local CPU?
> > So I think it doesn't care about the other CPUs (IOW, it should not touched by
> > other CPUs), so it only considers UP case. E.g. on x86, arch_cmpxchg_local() is
> > defined as raw "cmpxchg" without lock prefix.
> > 
> > #define __cmpxchg_local(ptr, old, new, size)                            \
> >         __raw_cmpxchg((ptr), (old), (new), (size), "")
> > 
> 
> Yes, you're right; sorry for the noise.
> 
> For your original patch:
> 
> Acked-by: Mark Rutland <mark.rutland@arm.com>
> 

Geert, what's your opinion on this?

Adrian

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