linux-kernel - Re: [RFC][PATCH] rcu: Use WRITE_ONCE in RCU_INIT

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Message-ID: <20150602162544.GI5989@linux.vnet.ibm.com>
Date:	Tue, 2 Jun 2015 09:25:44 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	josh@...htriplett.org, rostedt@...dmis.org,
	mathieu.desnoyers@...icios.com, laijs@...fujitsu.com,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] rcu: Use WRITE_ONCE in RCU_INIT_POINTER

On Tue, Jun 02, 2015 at 05:26:48PM +0200, Peter Zijlstra wrote:
> 
> For the paranoid amongst us GCC would be in its right to use byte stores
> to write our NULL value, tell it not to do that.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Good point, queued for 4.3.

							Thanx, Paul

> ---
>  include/linux/rcupdate.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 33a056bb886f..e173847b6543 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -1046,7 +1046,7 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
>  #define RCU_INIT_POINTER(p, v) \
>  	do { \
>  		rcu_dereference_sparse(p, __rcu); \
> -		p = RCU_INITIALIZER(v); \
> +		WRITE_ONCE(p, RCU_INITIALIZER(v)); \
>  	} while (0)
> 
>  /**
> 

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