Re: [PATCH] CodeSamples/count: Use READ_ONCE/WRITE_ONCE in count_nonatomic.c

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Wed, Sep 12, 2018 at 07:53:24PM +0900, Akira Yokosawa wrote:
> >From 13fa1b9b162483df5d88b7aefe408a4e17e83338 Mon Sep 17 00:00:00 2001
> From: Akira Yokosawa <akiyks@gmail.com>
> Date: Wed, 12 Sep 2018 19:27:41 +0900
> Subject: [PATCH] CodeSamples/count: Use READ_ONCE/WRITE_ONCE in count_nonatomic.c
> 
> Without them, inlined accesses can be optimized away by "-O3".

That code was written in a far more innocent time when compilers were
far less aggressive, wasn't it?

Great catch, both on the data and on the code, thank you!  Applied and
pushed.

							Thanx, Paul

> Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
> ---
>  CodeSamples/count/count_nonatomic.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/CodeSamples/count/count_nonatomic.c b/CodeSamples/count/count_nonatomic.c
> index 90979c5..50df475 100644
> --- a/CodeSamples/count/count_nonatomic.c
> +++ b/CodeSamples/count/count_nonatomic.c
> @@ -25,12 +25,12 @@ unsigned long counter = 0;
> 
>  __inline__ void inc_count(void)
>  {
> -	counter++;
> +	WRITE_ONCE(counter, READ_ONCE(counter) + 1);
>  }
> 
>  __inline__ unsigned long read_count(void)
>  {
> -	return counter;
> +	return READ_ONCE(counter);
>  }
> 
>  __inline__ void count_init(void)
> -- 
> 2.7.4
> 
>