Re: [PATCH net-next v2] rds: synchronize info callbacks with module unload

[Paolo Abeni <pabeni@redhat.com>]

Hi,

It looks like I was too optimistic in my previous reply.

On 7/27/26 7:48 PM, Chengfeng Ye wrote:
> @@ -78,8 +80,13 @@ void rds_info_register_func(int optname, rds_info_func func)
>  	BUG_ON(optname < RDS_INFO_FIRST || optname > RDS_INFO_LAST);
>  
>  	spin_lock(&rds_info_lock);
> -	BUG_ON(rds_info_funcs[offset]);
> -	rds_info_funcs[offset] = func;
> +	/* Validate the latest published slot value. */
> +	if (WARN_ON_ONCE(smp_load_acquire(&rds_info_funcs[offset]))) {

This read is under the same lock that perform the store. It's totally
unclear why smp_load_acquire() would be needed here. Very reasonably
it's not.

> +		spin_unlock(&rds_info_lock);
> +		return;
> +	}
> +	/* Pair with lockless callback lookup. */
> +	smp_store_release(&rds_info_funcs[offset], func);
>  	spin_unlock(&rds_info_lock);
>  }
>  EXPORT_SYMBOL_GPL(rds_info_register_func);
> @@ -91,9 +98,15 @@ void rds_info_deregister_func(int optname, rds_info_func func)
>  	BUG_ON(optname < RDS_INFO_FIRST || optname > RDS_INFO_LAST);
>  
>  	spin_lock(&rds_info_lock);
> -	BUG_ON(rds_info_funcs[offset] != func);
> -	rds_info_funcs[offset] = NULL;
> +	/* Validate the latest published slot value. */
> +	if (WARN_ON_ONCE(smp_load_acquire(&rds_info_funcs[offset]) != func)) {

Same here.

/P