Messages in this thread | | | Date | Wed, 25 Oct 2023 19:06:38 +0800 | Subject | Re: [PATCH] locking/atomic: sh: Use generic_cmpxchg_local for arch_cmpxchg_local() | From | "wuqiang.matt" <> |
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On 2023/10/25 09:51, wuqiang.matt wrote: > On 2023/10/25 07:42, Masami Hiramatsu (Google) 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? > > asm-generic/cmpxchg.h is only for UP, will throw an error for SMP building: > > #ifdef CONFIG_SMP > #error "Cannot use generic cmpxchg on SMP" > #endif
Sorry that I just noticed Masami's patch has asm-generic/cmpxchg-local.h included, not asm-generic/cmpxchg.h. cmpxchg.h does throw an error for SMP configs, but cmpxchg-local.h doesn't.
> SH arch seems it does have SMP systems. The arch/sh/include/asm/cmpxchg.h has > the following codes: > > #if defined(CONFIG_GUSA_RB) > #include <asm/cmpxchg-grb.h> > #elif defined(CONFIG_CPU_SH4A) > #include <asm/cmpxchg-llsc.h> > #elif defined(CONFIG_CPU_J2) && defined(CONFIG_SMP) > #include <asm/cmpxchg-cas.h> > #else > #include <asm/cmpxchg-irq.h> > #endif > >> 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), "") >> >> >> Thank you, >> >> >>> >>> I think the right thing to do here is to define arch_cmpxchg_local() in terms >>> of arch_cmpxchg(), i.e. at the bottom of arch/sh's <asm/cmpxchg.h> add: >>> >>> #define arch_cmpxchg_local arch_cmpxchg > > I agree too. Might not be performance optimized but guarantees correctness. > >>> Mark. >>> >>>> >>>> Reported-by: kernel test robot <lkp@intel.com> >>>> Closes: >>>> https://lore.kernel.org/oe-kbuild-all/202310241310.Ir5uukOG-lkp@intel.com/ >>>> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> >>>> --- >>>> arch/sh/include/asm/cmpxchg.h | 2 ++ >>>> 1 file changed, 2 insertions(+) >>>> >>>> diff --git a/arch/sh/include/asm/cmpxchg.h b/arch/sh/include/asm/cmpxchg.h >>>> index 288f6f38d98f..e920e61fb817 100644 >>>> --- a/arch/sh/include/asm/cmpxchg.h >>>> +++ b/arch/sh/include/asm/cmpxchg.h >>>> @@ -71,4 +71,6 @@ static inline unsigned long __cmpxchg(volatile void * >>>> ptr, unsigned long old, >>>> (unsigned long)_n_, sizeof(*(ptr))); \ >>>> }) >>>> +#include <asm-generic/cmpxchg-local.h> >>>> + >>>> #endif /* __ASM_SH_CMPXCHG_H */ >>>> >> >> >
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