On Mon, Nov 04, 2013 at 10:36:17PM +0200, Michael S. Tsirkin wrote:
> srcu read lock/unlock include a full memory barrier
> but that's an implementation detail.
> Add an API for make memory fencing explicit for
> users that need this barrier, to make sure we
> can change it as needed without breaking all users.
>
> Acked-by: "Paul E. McKenney" <paul...@linux.vnet.ibm.com>
> Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
Reviewed-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> ---
> include/linux/srcu.h | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/include/linux/srcu.h b/include/linux/srcu.h
> index c114614..9b058ee 100644
> --- a/include/linux/srcu.h
> +++ b/include/linux/srcu.h
> @@ -237,4 +237,18 @@ static inline void srcu_read_unlock(struct srcu_struct
> *sp, int idx)
> __srcu_read_unlock(sp, idx);
> }
>
> +/**
> + * smp_mb__after_srcu_read_unlock - ensure full ordering after
> srcu_read_unlock
> + *
> + * Converts the preceding srcu_read_unlock into a two-way memory barrier.
> + *
> + * Call this after srcu_read_unlock, to guarantee that all memory operations
> + * that occur after smp_mb__after_srcu_read_unlock will appear to happen
> after
> + * the preceding srcu_read_unlock.
> + */
> +static inline void smp_mb__after_srcu_read_unlock(void)
> +{
> + /* __srcu_read_unlock has smp_mb() internally so nothing to do here. */
> +}
> +
> #endif
> --
> MST
>
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