Re: [RFC PATCH] locking/percpu-rwsem: use this_cpu_{inc|dec}() for read_count

[peterz]

On Fri, Sep 18, 2020 at 12:01:12PM +0200, peterz@xxxxxxxxxxxxx wrote:
> @@ -198,7 +198,9 @@ EXPORT_SYMBOL_GPL(__percpu_down_read);
>   */
>  static bool readers_active_check(struct percpu_rw_semaphore *sem)
>  {
> -	if (per_cpu_sum(*sem->read_count) != 0)
> +	u64 sum = per_cpu_sum(*(u64 *)sem->read_count);
> +
> +	if (sum + (sum >> 32))

That obviously wants to be:

	if ((u32)(sum + (sum >> 32)))

>  		return false;
>  
>  	/*