Subject: Re: [PATCH] net: dst_release() cleanup

From: Stephen Hemminger <[email-masked]>
Date: Mon, 7 Dec 2009 09:17:46 -0800

On Sat, 05 Dec 2009 13:02:13 +0100
Eric Dumazet <[email-masked]> wrote:

> atomic_dec_return() is a full memory barrier, we can omit
> the smp_mb__before_atomic_dec() call.
> 
> Signed-off-by: Eric Dumazet <[email-masked]>
> ---
>  net/core/dst.c |    9 ++-------
>  1 file changed, 2 insertions(+), 7 deletions(-)
> 
> diff --git a/net/core/dst.c b/net/core/dst.c
> index 57bc4d5..cdec1d1 100644
> --- a/net/core/dst.c
> +++ b/net/core/dst.c
> @@ -262,13 +262,8 @@ again:
>  
>  void dst_release(struct dst_entry *dst)
>  {
> -	if (dst) {
> -               int newrefcnt;
> -
> -		smp_mb__before_atomic_dec();
> -               newrefcnt = atomic_dec_return(&dst->__refcnt);
> -               WARN_ON(newrefcnt < 0);
> -	}
> +	if (dst)
> +		WARN_ON(atomic_dec_return(&dst->__refcnt) < 0);
>  }
>  EXPORT_SYMBOL(dst_release);

I don't like to put actual necessary code in WARN or BUG macro
args because some embedded type developer is likely to build
with

#define WARN_ON(x)

to get rid of all warnings.