Re: [PATCH v3 3/5] asm-generic: barrier: Add smp_cond_load_acquire_timewait()

[Catalin Marinas <catalin.marinas@arm.com>]

On Thu, Jun 26, 2025 at 09:48:03PM -0700, Ankur Arora wrote:
> diff --git a/arch/arm64/include/asm/rqspinlock.h b/arch/arm64/include/asm/rqspinlock.h
> index 9ea0a74e5892..f1b6a428013e 100644
> --- a/arch/arm64/include/asm/rqspinlock.h
> +++ b/arch/arm64/include/asm/rqspinlock.h
> @@ -86,7 +86,7 @@
>  
>  #endif
>  
> -#define res_smp_cond_load_acquire(v, c) smp_cond_load_acquire_timewait(v, c, 0, 1)
> +#define res_smp_cond_load_acquire(v, c) smp_cond_load_acquire_timewait(v, c, 0ULL, 1ULL, 0)
>  
>  #include <asm-generic/rqspinlock.h>
>  
> diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
> index 8299c57d1110..dd7c9ca2dff3 100644
> --- a/include/asm-generic/barrier.h
> +++ b/include/asm-generic/barrier.h
> @@ -388,6 +388,28 @@ static inline u64 ___smp_cond_spinwait(u64 now, u64 prev, u64 end,
>  	(typeof(*ptr))_val;						\
>  })
>  
> +/**
> + * smp_cond_load_acquire_timewait() - (Spin) wait for cond with ACQUIRE ordering
> + * until a timeout expires.
> + *
> + * Arguments: same as smp_cond_load_relaxed_timeout().
> + *
> + * Equivalent to using smp_cond_load_acquire() on the condition variable with
> + * a timeout.
> + */
> +#ifndef smp_cond_load_acquire_timewait
> +#define smp_cond_load_acquire_timewait(ptr, cond_expr,			\
> +				       time_expr, time_end,		\
> +				       slack) ({			\
> +	__unqual_scalar_typeof(*ptr) _val;				\
> +	_val = smp_cond_load_relaxed_timewait(ptr, cond_expr,		\
> +					      time_expr, time_end,	\
> +					      slack);			\
> +	/* Depends on the control dependency of the wait above. */	\
> +	smp_acquire__after_ctrl_dep();					\
> +	(typeof(*ptr))_val;						\
> +})
> +#endif

Using #ifndef in the generic file is the correct thing to do, it allows
architectures to redefine it. Why we have a similar #ifndef in the arm64
rqspinlock.h, no idea, none of the arm64 maintainers acked that patch
(shouldn't have gone in really, we were still discussing the
implementation at the time; I also think it's slightly wrong).

Your change above to rqspinlock.h makes this even more confusing when
you look at the overall result with all the patches applied. We end up
with the same macro in asm/rqspinlock.h but with different number of
arguments.

I'd start with ripping out the current arm64 implementation, add a
generic implementation to barrier.h and then override it in the arch
code.

-- 
Catalin