Re: [PATCH v7 5/6] MCS Lock: allow architectures to hook in tocontended paths

[Peter Zijlstra]

On Thu, Jan 16, 2014 at 04:08:31PM -0800, Tim Chen wrote:
> +#ifndef arch_mcs_spin_lock_contended
> +/*
> + * Using smp_load_acquire() provides a memory barrier that ensures
> + * subsequent operations happen after the lock is acquired.
> + */
> +#define arch_mcs_spin_lock_contended(l)					\
> +	while (!(smp_load_acquire(l))) {				\
> +		arch_mutex_cpu_relax();					\
> +	}
> +#endif

I think that wants to be:

#define arch_mcs_spin_lock_contended(l)				\
do {								\
	while (!smp_load_acquire(l))				\
		arch_mutex_cpu_relax();				\
} while (0)

So that we properly eat the ';' in: arch_mcs_spin_lock_contended(l);.

> +#ifndef arch_mcs_spin_unlock_contended
> +/*
> + * smp_store_release() provides a memory barrier to ensure all
> + * operations in the critical section has been completed before
> + * unlocking.
> + */
> +#define arch_mcs_spin_unlock_contended(l)				\
> +	smp_store_release((l), 1)
>  #endif
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