Re: [RFC PATCH] MIPS: cmpxchg64() and HAVE_VIRT_CPU_ACCOUNTING_GEN don't work for 32-bit SMP

[James Hogan <james.hogan@mips.com>]

On Wed, Oct 04, 2017 at 03:46:14AM +0100, Ben Hutchings wrote:
> __cmpxchg64_local_generic() is atomic only w.r.t tasks and interrupts
> on the same CPU (that's what the 'local' means).  We can't use it to
> implement cmpxchg64() in SMP configurations.
> 
> So, for 32-bit SMP configurations:
> 
> - Don't define cmpxchg64()
> - Don't enable HAVE_VIRT_CPU_ACCOUNTING_GEN, which requires it
> 
> Fixes: e2093c7b03c1 ("MIPS: Fall back to generic implementation of ...")
> Fixes: bb877e96bea1 ("MIPS: Add support for full dynticks CPU time accounting")
> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

Thanks, looks reasonable to me

Applied

Cheers
James

> ---
>  arch/mips/Kconfig               | 2 +-
>  arch/mips/include/asm/cmpxchg.h | 2 ++
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> index cb7fcc4216fd..1e23f8455b7d 100644
> --- a/arch/mips/Kconfig
> +++ b/arch/mips/Kconfig
> @@ -64,7 +64,7 @@ config MIPS
>  	select HAVE_PERF_EVENTS
>  	select HAVE_REGS_AND_STACK_ACCESS_API
>  	select HAVE_SYSCALL_TRACEPOINTS
> -	select HAVE_VIRT_CPU_ACCOUNTING_GEN
> +	select HAVE_VIRT_CPU_ACCOUNTING_GEN if 64BIT || !SMP
>  	select IRQ_FORCED_THREADING
>  	select MODULES_USE_ELF_RELA if MODULES && 64BIT
>  	select MODULES_USE_ELF_REL if MODULES
> diff --git a/arch/mips/include/asm/cmpxchg.h b/arch/mips/include/asm/cmpxchg.h
> index 903f3bf48419..ae2b4583b486 100644
> --- a/arch/mips/include/asm/cmpxchg.h
> +++ b/arch/mips/include/asm/cmpxchg.h
> @@ -202,8 +202,10 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
>  #else
>  #include <asm-generic/cmpxchg-local.h>
>  #define cmpxchg64_local(ptr, o, n) __cmpxchg64_local_generic((ptr), (o), (n))
> +#ifndef CONFIG_SMP
>  #define cmpxchg64(ptr, o, n) cmpxchg64_local((ptr), (o), (n))
>  #endif
> +#endif
>  
>  #undef __scbeqz
>