From 02b99b38f3d96c77cf0a368d99952aa372dfe58a Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sat, 9 Nov 2019 10:45:47 -0800 Subject: rcu: Add a hlist_nulls_unhashed_lockless() function This commit adds an hlist_nulls_unhashed_lockless() to allow lockless checking for whether or note an hlist_nulls_node is hashed or not. While in the area, this commit also adds a docbook comment to the existing hlist_nulls_unhashed() function. Signed-off-by: Paul E. McKenney --- include/linux/list_nulls.h | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) (limited to 'include/linux/list_nulls.h') diff --git a/include/linux/list_nulls.h b/include/linux/list_nulls.h index 1ecd35664e0d..fa6e8471bd22 100644 --- a/include/linux/list_nulls.h +++ b/include/linux/list_nulls.h @@ -56,11 +56,33 @@ static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr) return ((unsigned long)ptr) >> 1; } +/** + * hlist_nulls_unhashed - Has node been removed and reinitialized? + * @h: Node to be checked + * + * Not that not all removal functions will leave a node in unhashed state. + * For example, hlist_del_init_rcu() leaves the node in unhashed state, + * but hlist_nulls_del() does not. + */ static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h) { return !h->pprev; } +/** + * hlist_nulls_unhashed_lockless - Has node been removed and reinitialized? + * @h: Node to be checked + * + * Not that not all removal functions will leave a node in unhashed state. + * For example, hlist_del_init_rcu() leaves the node in unhashed state, + * but hlist_nulls_del() does not. Unlike hlist_nulls_unhashed(), this + * function may be used locklessly. + */ +static inline int hlist_nulls_unhashed_lockless(const struct hlist_nulls_node *h) +{ + return !READ_ONCE(h->pprev); +} + static inline int hlist_nulls_empty(const struct hlist_nulls_head *h) { return is_a_nulls(READ_ONCE(h->first)); -- cgit