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SubjectRe: [PATCH tip/core/rcu 2/3] srcu: Force full grace-period ordering

* Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:

> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 357b32aaea48..5fdfe874229e 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -1175,11 +1175,11 @@ do { \
> * if the UNLOCK and LOCK are executed by the same CPU or if the
> * UNLOCK and LOCK operate on the same lock variable.
> */
> -#ifdef CONFIG_PPC
> +#ifdef CONFIG_ARCH_WEAK_RELACQ
> #define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */
> -#else /* #ifdef CONFIG_PPC */
> +#else /* #ifdef CONFIG_ARCH_WEAK_RELACQ */
> #define smp_mb__after_unlock_lock() do { } while (0)
> -#endif /* #else #ifdef CONFIG_PPC */
> +#endif /* #else #ifdef CONFIG_ARCH_WEAK_RELACQ */
>
>

So at the risk of sounding totally pedantic, why not structure it like the
existing smp_mb__before/after*() primitives in barrier.h?

That allows asm-generic/barrier.h to pick up the definition - for example in the
case of smp_acquire__after_ctrl_dep() we do:

#ifndef smp_acquire__after_ctrl_dep
#define smp_acquire__after_ctrl_dep() smp_rmb()
#endif

Which allows Tile to relax it:

arch/tile/include/asm/barrier.h:#define smp_acquire__after_ctrl_dep() barrier()

I.e. I'd move the API definition out of rcupdate.h and into barrier.h - even
though tree-RCU is the only user of this barrier type.

Thanks,

Ingo

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