[PATCH libdrm] atomic: fix atomic_add_unless() fallback's return value

[Eric Engestrom]

On Thursday, 2017-03-16 00:08:59 +0000, Eric Engestrom wrote:
> According to the kernel documentation:
>   Returns non-zero if @v was not @u, and zero otherwise.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100077
> Fixes: 63fc571863aa64683400 ("atomic: add atomic_add_unless()")
> Signed-off-by: David Shao <davshao at gmail.com>
> Reviewed-by: Eric Engestrom <eric at engestrom.ch>
> Signed-off-by: Eric Engestrom <eric at engestrom.ch>

That last s-o-b was added automatically, by mistake. I'll remove it when
pushing this.

This patch seems trivial to verify, can someone confirm this is right?

/me is about ~94% sure, but doesn't know much about atomic ops and their
return value convention.

I checked the kernel and it does what libdrm does after this patch, so
either one should be fixed; I'm assuming kernel is right and libdrm
needs fixing, hence this patch.

Cheers,
  Eric

> ---
>  xf86atomic.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/xf86atomic.h b/xf86atomic.h
> index 922b37da..ecb1ba86 100644
> --- a/xf86atomic.h
> +++ b/xf86atomic.h
> @@ -111,7 +111,7 @@ static inline int atomic_add_unless(atomic_t *v, int add, int unless)
>  	c = atomic_read(v);
>  	while (c != unless && (old = atomic_cmpxchg(v, c, c + add)) != c)
>  		c = old;
> -	return c == unless;
> +	return c != unless;
>  }
>  
>  #endif
> -- 
> Cheers,
>   Eric
>