Man page 9 : seq_hlist_next_rcu

seq_hlist_next_rcu - move to the next position of the hlist protected by RCU

struct hlist_node * seq_hlist_next_rcu(void *  v , struct hlist_head *  head , loff_t *  ppos );

v
    the current iterator

head
    the head of the hlist

ppos
    the current position

Called at seq_file->op->next.

This list-traversal primitive may safely run concurrently with the _rcu list-mutation primitives such as hlist_add_head_rcu as long as the traversal is guarded by rcu_read_lock.