list_del_rcu — deletes entry from list without re-initialization
void list_del_rcu (struct list_head * entry);
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, it means that we can not poison the forward pointers that 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_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.
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.