netdev - Re: [PATCH RFC net-next 01/14] rculist_bl: add hlist_bl_for_each_entry_continue

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Date: Tue, 15 Aug 2023 11:39:43 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Julian Anastasov <ja@....bg>
Cc: Simon Horman <horms@...ge.net.au>, lvs-devel@...r.kernel.org,
	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
	rcu@...r.kernel.org, Dust Li <dust.li@...ux.alibaba.com>,
	Jiejian Wu <jiejian@...ux.alibaba.com>,
	Jiri Wiesner <jwiesner@...e.de>
Subject: Re: [PATCH RFC net-next 01/14] rculist_bl: add
 hlist_bl_for_each_entry_continue_rcu

On Tue, Aug 15, 2023 at 08:30:18PM +0300, Julian Anastasov wrote:
> Add hlist_bl_for_each_entry_continue_rcu and hlist_bl_next_rcu
> 
> Signed-off-by: Julian Anastasov <ja@....bg>
> ---
>  include/linux/rculist_bl.h | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/include/linux/rculist_bl.h b/include/linux/rculist_bl.h
> index 0b952d06eb0b..93a757793d83 100644
> --- a/include/linux/rculist_bl.h
> +++ b/include/linux/rculist_bl.h
> @@ -24,6 +24,10 @@ static inline struct hlist_bl_node *hlist_bl_first_rcu(struct hlist_bl_head *h)
>  		((unsigned long)rcu_dereference_check(h->first, hlist_bl_is_locked(h)) & ~LIST_BL_LOCKMASK);
>  }
>  
> +/* return the next element in an RCU protected list */
> +#define hlist_bl_next_rcu(node)	\
> +	(*((struct hlist_bl_node __rcu **)(&(node)->next)))
> +
>  /**
>   * hlist_bl_del_rcu - deletes entry from hash list without re-initialization
>   * @n: the element to delete from the hash list.
> @@ -98,4 +102,17 @@ static inline void hlist_bl_add_head_rcu(struct hlist_bl_node *n,
>  		({ tpos = hlist_bl_entry(pos, typeof(*tpos), member); 1; }); \
>  		pos = rcu_dereference_raw(pos->next))
>  
> +/**
> + * hlist_bl_for_each_entry_continue_rcu - iterate over a list continuing after
> + *   current point

Please add a comment to the effect that the element continued from
must have been either: (1) Iterated to within the same RCU read-side
critical section or (2) Nailed down using some lock, reference count,
or whatever suffices to keep the continued-from element from being freed
in the meantime.

							Thanx, Paul

> + * @tpos:	the type * to use as a loop cursor.
> + * @pos:	the &struct hlist_bl_node to use as a loop cursor.
> + * @member:	the name of the hlist_bl_node within the struct.
> + */
> +#define hlist_bl_for_each_entry_continue_rcu(tpos, pos, member)		\
> +	for (pos = rcu_dereference_raw(hlist_bl_next_rcu(&(tpos)->member)); \
> +	     pos &&							\
> +	     ({ tpos = hlist_bl_entry(pos, typeof(*tpos), member); 1; }); \
> +	     pos = rcu_dereference_raw(hlist_bl_next_rcu(pos)))
> +
>  #endif
> -- 
> 2.41.0
> 
>