netdev - Re: [PATCH net-next v1 1/3] rculist: Add __hlist_nulls_replace_rcu() and hlist_nulls_replace_init

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAAVpQUBuV9ixMheieH137YNxZsKAZhQekjudpiw-=7DsvxV7BA@mail.gmail.com>
Date: Mon, 15 Sep 2025 15:50:39 -0700
From: Kuniyuki Iwashima <kuniyu@...gle.com>
To: xuanqiang.luo@...ux.dev
Cc: edumazet@...gle.com, kerneljasonxing@...il.com, davem@...emloft.net, 
	kuba@...nel.org, netdev@...r.kernel.org, 
	Xuanqiang Luo <luoxuanqiang@...inos.cn>
Subject: Re: [PATCH net-next v1 1/3] rculist: Add __hlist_nulls_replace_rcu()
 and hlist_nulls_replace_init_rcu()

On Mon, Sep 15, 2025 at 12:04 AM <xuanqiang.luo@...ux.dev> wrote:
>
> From: Xuanqiang Luo <luoxuanqiang@...inos.cn>
>
> Add two functions to atomically replace RCU-protected hlist_nulls entries.
>
> Signed-off-by: Xuanqiang Luo <luoxuanqiang@...inos.cn>
> ---
>  include/linux/rculist_nulls.h | 62 +++++++++++++++++++++++++++++++++++
>  1 file changed, 62 insertions(+)
>
> diff --git a/include/linux/rculist_nulls.h b/include/linux/rculist_nulls.h
> index 89186c499dd4..eaa3a0d2f206 100644
> --- a/include/linux/rculist_nulls.h
> +++ b/include/linux/rculist_nulls.h
> @@ -152,6 +152,68 @@ static inline void hlist_nulls_add_fake(struct hlist_nulls_node *n)
>         n->next = (struct hlist_nulls_node *)NULLS_MARKER(NULL);
>  }
>
> +/**
> + * __hlist_nulls_replace_rcu - replace an old entry by a new one
> + * @old: the element to be replaced
> + * @new: the new element to insert
> + *
> + * Description:
> + * Replace the old entry with the new one in a RCU-protected hlist_nulls, while
> + * permitting racing traversals.
> + *
> + * The caller must take whatever precautions are necessary (such as holding
> + * appropriate locks) to avoid racing with another list-mutation primitive, such
> + * as hlist_nulls_add_head_rcu() or hlist_nulls_del_rcu(), running on this same
> + * list.  However, it is perfectly legal to run concurrently with the _rcu
> + * list-traversal primitives, such as hlist_nulls_for_each_entry_rcu().
> + */
> +static inline void __hlist_nulls_replace_rcu(struct hlist_nulls_node *old,
> +                                            struct hlist_nulls_node *new)
> +{
> +       struct hlist_nulls_node *next = old->next;
> +
> +       new->next = next;
> +       WRITE_ONCE(new->pprev, old->pprev);
> +       rcu_assign_pointer(*(struct hlist_nulls_node __rcu **)new->pprev, new);
> +       if (!is_a_nulls(next))
> +               WRITE_ONCE(new->next->pprev, &new->next);
> +}
> +
> +/**
> + * hlist_nulls_replace_init_rcu - replace an old entry by a new one and
> + * initialize the old
> + * @old: the element to be replaced
> + * @new: the new element to insert
> + *
> + * Description:
> + * Replace the old entry with the new one in a RCU-protected hlist_nulls, while
> + * permitting racing traversals, and reinitialize the old entry.
> + *
> + * Return: true if the old entry was hashed and was replaced successfully, false
> + * otherwise.
> + *
> + * Note: hlist_nulls_unhashed() on the old node returns true after this.
> + * It is useful for RCU based read lockfree traversal if the writer side must
> + * know if the list entry is still hashed or already unhashed.
> + *
> + * The caller must take whatever precautions are necessary (such as holding
> + * appropriate locks) to avoid racing with another list-mutation primitive, such
> + * as hlist_nulls_add_head_rcu() or hlist_nulls_del_rcu(), running on this same
> + * list. However, it is perfectly legal to run concurrently with the _rcu
> + * list-traversal primitives, such as hlist_nulls_for_each_entry_rcu().
> + */
> +static inline bool hlist_nulls_replace_init_rcu(struct hlist_nulls_node *old,
> +                                               struct hlist_nulls_node *new)
> +{
> +       if (!hlist_nulls_unhashed(old)) {

This is already checked by __sk_nulls_replace_node_init_rcu().


> +               __hlist_nulls_replace_rcu(old, new);
> +               old->pprev = NULL;
> +               return true;
> +       }
> +
> +       return false;
> +}
> +
>  /**
>   * hlist_nulls_for_each_entry_rcu - iterate over rcu list of given type
>   * @tpos:      the type * to use as a loop cursor.
> --
> 2.27.0
>