From: Xuanqiang Luo Add two functions to atomically replace RCU-protected hlist_nulls entries. Signed-off-by: Xuanqiang Luo --- include/linux/rculist_nulls.h | 61 +++++++++++++++++++++++++++++++++++ 1 file changed, 61 insertions(+) diff --git a/include/linux/rculist_nulls.h b/include/linux/rculist_nulls.h index 89186c499dd4..8ed604f65a3e 100644 --- a/include/linux/rculist_nulls.h +++ b/include/linux/rculist_nulls.h @@ -152,6 +152,67 @@ 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)) { + __hlist_nulls_replace_rcu(old, new); + WRITE_ONCE(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. -- 2.25.1