linux-kernel - Re: [PATCH tip/core/rcu 08/14] rcu: Remove return value from rcu_assign

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Message-ID: <20120615205355.GL31184@leaf>
Date:	Fri, 15 Jun 2012 13:53:55 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	fweisbec@...il.com, patches@...aro.org
Subject: Re: [PATCH tip/core/rcu 08/14] rcu: Remove return value from
 rcu_assign_pointer()

On Fri, Jun 15, 2012 at 01:13:09PM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paulmck@...ux.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@...icios.com>
> Reported-by: Josh Triplett <josh@...htriplett.org>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

Reviewed-by: Josh Triplett <josh@...htriplett.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
> 
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