Re: [PATCH tip/core/rcu 08/14] rcu: Remove return value from rcu_assign_pointer()

Josh Triplett
2012-06-15T20:54:10Z

On Fri, Jun 15, 2012 at 01:13:09PM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
>
> The return value from rcu_assign_pointer() is not used, and using it
> would be quite ugly, for example:
>
> q = rcu_assign_pointer(global_p, p);
>
> To prevent this sort of ugliness from spreading, this commit wraps
> rcu_assign_pointer() in a do-while loop.
>
> Reported-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Reported-by: Josh Triplett <josh@joshtriplett.org>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Reviewed-by: Josh Triplett <josh@joshtriplett.org>

> include/linux/rcupdate.h | 6 +++---
> 1 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index f2cca02..2f6ec55 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -514,10 +514,10 @@ static inline void rcu_preempt_sleep_check(void)
> (_________p1); \
> })
> #define __rcu_assign_pointer(p, v, space) \
> - ({ \
> + do { \
> smp_wmb(); \
> (p) = (typeof(*v) __force space *)(v); \
> - })
> + } while (0)
>
>
> /**
> @@ -852,7 +852,7 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
> *
> * Assigns the specified value to the specified RCU-protected
> * pointer, ensuring that any concurrent RCU readers will see
> - * any prior initialization. Returns the value assigned.
> + * any prior initialization.
> *
> * Inserts memory barriers on architectures that require them
> * (which is most of them), and also prevents the compiler from
> --
> 1.7.8
>