- * The list may not be empty when list_empty_rcu checks it, but it may be when
- * list_first_entry_rcu rereads the ->next pointer.
- *
- * Rereading the ->next pointer is not a problem for list_empty() and
- * list_first_entry() because they would be protected by a lock that blocks
- * writers.
+ * The list might be non-empty when list_empty_rcu() checks it, but it
+ * might have become empty by the time that list_first_entry_rcu() rereads
+ * the ->next pointer, which would result in a SEGV.
+ *
+ * When not using RCU, it is OK for list_first_entry() to re-read that
+ * pointer because both functions should be protected by some lock that
+ * blocks writers.
+ *
+ * When using RCU, list_empty() uses READ_ONCE() to fetch the
+ * RCU-protected ->next pointer and then compares it to the address of the
+ * list head. However, it neither dereferences this pointer nor provides
+ * this pointer to its caller. Thus, READ_ONCE() suffices (that is,
+ * rcu_dereference() is not needed), which means that list_empty() can be
+ * used anywhere you would want to use list_empty_rcu(). Just don't
+ * expect anything useful to happen if you do a subsequent lockless
+ * call to list_first_entry_rcu()!!!