Provide a helper to traverse an RCU-protected doubly linked list in the reverse order. Also add a corresponding helper to delete entries from the linked list, which takes care to see that we don't poison either of the pointers (->prev and ->next), since it is legal to run an rcu list-traversal operation (in either forward/reverse direction) concurrently.
Signed-off-by: Srivatsa S. Bhat <[email protected]> --- include/linux/rculist.h | 46 ++++++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 46 insertions(+), 0 deletions(-) diff --git a/include/linux/rculist.h b/include/linux/rculist.h index e0f0fab..6f22a13 100644 --- a/include/linux/rculist.h +++ b/include/linux/rculist.h @@ -118,6 +118,36 @@ static inline void list_del_rcu(struct list_head *entry) } /** + * list_del_bidir_rcu - deletes entry from list without re-initialization. + * Useful when one wants to perform bidirectional traversal of the list. + * + * @entry: the element to delete from the list. + * + * Note: list_empty() on entry does not return true after this, + * the entry is in an undefined state. It is useful for RCU based + * lockfree traversal. + * + * In particular, since we should be able to traverse this list in both + * directions, it means that we can not poison either of the pointers + * (->prev and ->next) because they may still be used for walking the list. + * + * The caller must take whatever precautions are necessary (such as holding + * appropriate locks) to avoid racing with another list-mutation primitive, + * such as list_del_bidir_rcu() or list_add_rcu(), running on this same list. + * However, it is perfectly legal to run concurrently with the _rcu + * list-traversal primitives, such as list_for_each_entry_rcu() or + * list_for_each_entry_reverse_rcu(). + * + * Note that the caller is not permitted to immediately free the newly deleted + * entry. Instead, either synchronize_rcu() or call_rcu() must be used to + * defer freeing until an RCU grace period has elapsed. + */ +static inline void list_del_bidir_rcu(struct list_head *entry) +{ + __list_del_entry(entry); +} + +/** * hlist_del_init_rcu - deletes entry from hash list with re-initialization * @n: the element to delete from the hash list. * @@ -286,6 +316,22 @@ static inline void list_splice_init_rcu(struct list_head *list, &pos->member != (head); \ pos = list_entry_rcu(pos->member.next, typeof(*pos), member)) +/** + * list_for_each_entry_reverse_rcu - iterate backwards over rcu list of given + * type + * + * @pos: the type * to use as a loop cursor. + * @head: the head for your list. + * @member: the name of the list_struct within the struct. + * + * This list-traversal primitive may safely run concurrently with + * the _rcu list-mutation primitives such as list_add_rcu() + * as long as the traversal is guarded by rcu_read_lock(). + */ +#define list_for_each_entry_reverse_rcu(pos, head, member) \ + for (pos = list_entry_rcu((head)->prev, typeof(*pos), member); \ + &pos->member != (head); \ + pos = list_entry_rcu(pos->member.prev, typeof(*pos), member)) /** * list_for_each_continue_rcu -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
