Fix error of __list_find

The node on the linked list should follow the ordering by its key.
However, the function list_insert doesn't actually do this because
of the wrong implementation of __list_find.

There are three main fixes in this patch. First,
once we should do synchronization, we have to iterate the list
again but not return from the function. Second, the while loop should
iterate until the last node but not the second last one. Finally,
under the normal situation that the tail node with key UINTPTR_MAX should
not be deleted (unless the end of the program), some codes are never executed
which can be removed.

Author: RinHizakura

hp_list/main.c

@@ -230,14 +230,13 @@ static bool __list_find(list_t *list,
     if (atomic_load(prev) != get_unmarked(curr))
         goto try_again;
     while (true) {
-        if (!get_unmarked_node(curr))
-            return false;
         next = (list_node_t *) atomic_load(&get_unmarked_node(curr)->next);
         (void) list_hp_protect_ptr(list->hp, HP_NEXT, get_unmarked(next));
+        /* On a CAS failure, the search function, "__list_find", will simply have to
+           go backwards in the list until an unmarked element is found from which
+           the search in increasing key order can be started. */
         if (atomic_load(&get_unmarked_node(curr)->next) != (uintptr_t) next)
-            break;
-        if (get_unmarked(next) == atomic_load((atomic_uintptr_t *) &list->tail))
-            break;
+            goto try_again;
         if (atomic_load(prev) != get_unmarked(curr))
             goto try_again;
         if (get_unmarked_node(next) == next) {
@@ -259,11 +258,6 @@ static bool __list_find(list_t *list,
         curr = next;
         (void) list_hp_protect_release(list->hp, HP_CURR, get_unmarked(next));
     }
-    *par_curr = curr;
-    *par_prev = prev;
-    *par_next = next;
-
-    return false;
 }
 
 bool list_insert(list_t *list, list_key_t key)