linux-kernel - Re: [PATCH bpf-next 1/4] fprobe: use rhashtable

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Message-ID: <aId3ZSnlZRzoDUHC@krava>
Date: Mon, 28 Jul 2025 15:13:09 +0200
From: Jiri Olsa <olsajiri@...il.com>
To: Menglong Dong <menglong8.dong@...il.com>
Cc: alexei.starovoitov@...il.com, mhiramat@...nel.org, rostedt@...dmis.org,
	mathieu.desnoyers@...icios.com, hca@...ux.ibm.com,
	revest@...omium.org, linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next 1/4] fprobe: use rhashtable

On Mon, Jul 28, 2025 at 12:12:48PM +0800, Menglong Dong wrote:

SNIP

> +static const struct rhashtable_params fprobe_rht_params = {
> +	.head_offset		= offsetof(struct fprobe_hlist_node, hlist),
> +	.key_offset		= offsetof(struct fprobe_hlist_node, addr),
> +	.key_len		= sizeof_field(struct fprobe_hlist_node, addr),
> +	.hashfn			= fprobe_node_hashfn,
> +	.obj_hashfn		= fprobe_node_obj_hashfn,
> +	.obj_cmpfn		= fprobe_node_cmp,
> +	.automatic_shrinking	= true,
> +};
>  
>  /* Node insertion and deletion requires the fprobe_mutex */
>  static void insert_fprobe_node(struct fprobe_hlist_node *node)
>  {
> -	unsigned long ip = node->addr;
> -	struct fprobe_hlist_node *next;
> -	struct hlist_head *head;
> -
>  	lockdep_assert_held(&fprobe_mutex);
>  
> -	next = find_first_fprobe_node(ip);
> -	if (next) {
> -		hlist_add_before_rcu(&node->hlist, &next->hlist);
> -		return;
> -	}
> -	head = &fprobe_ip_table[hash_ptr((void *)ip, FPROBE_IP_HASH_BITS)];
> -	hlist_add_head_rcu(&node->hlist, head);
> +	rhashtable_insert_fast(&fprobe_ip_table, &node->hlist,
> +			       fprobe_rht_params);

onw that rhashtable_insert_fast can fail, I think insert_fprobe_node
needs to be able to fail as well

>  }
>  
>  /* Return true if there are synonims */
> @@ -92,9 +93,11 @@ static bool delete_fprobe_node(struct fprobe_hlist_node *node)
>  	/* Avoid double deleting */
>  	if (READ_ONCE(node->fp) != NULL) {
>  		WRITE_ONCE(node->fp, NULL);
> -		hlist_del_rcu(&node->hlist);
> +		rhashtable_remove_fast(&fprobe_ip_table, &node->hlist,
> +				       fprobe_rht_params);

I guess this one can't fail in here.. ?

jirka

>  	}
> -	return !!find_first_fprobe_node(node->addr);
> +	return !!rhashtable_lookup_fast(&fprobe_ip_table, &node->addr,
> +					fprobe_rht_params);
>  }
>  

SNIP