[bug report] maple_tree: add MAS_UNDERFLOW and MAS_OVERFLOW states

[Dan Carpenter]

Hello Liam R. Howlett,

The patch 234d37113ef0: "maple_tree: add MAS_UNDERFLOW and
MAS_OVERFLOW states" from Sep 21, 2023 (linux-next), leads to the
following Smatch static checker warning:

	lib/maple_tree.c:4653 mas_next_slot()
	warn: ignoring unreachable code.

lib/maple_tree.c
    4603 static void *mas_next_slot(struct ma_state *mas, unsigned long max, bool empty,
    4604                            bool set_overflow)
    4605 {
    4606         void __rcu **slots;
    4607         unsigned long *pivots;
    4608         unsigned long pivot;
    4609         enum maple_type type;
    4610         struct maple_node *node;
    4611         unsigned char data_end;
    4612         unsigned long save_point = mas->last;
    4613         void *entry;
    4614 
    4615 retry:
    4616         node = mas_mn(mas);
    4617         type = mte_node_type(mas->node);
    4618         pivots = ma_pivots(node, type);
    4619         data_end = ma_data_end(node, type, pivots, mas->max);
    4620         if (unlikely(mas_rewalk_if_dead(mas, node, save_point)))
    4621                 goto retry;
    4622 
    4623         if (mas->max >= max) {
    4624                 if (likely(mas->offset < data_end))
    4625                         pivot = pivots[mas->offset];
    4626                 else
    4627                         goto overflow;
    4628 
    4629                 if (unlikely(mas_rewalk_if_dead(mas, node, save_point)))
    4630                         goto retry;
    4631 
    4632                 if (pivot >= max)
    4633                         goto overflow;
    4634         }
    4635 
    4636         if (likely(mas->offset < data_end)) {
    4637                 mas->index = pivots[mas->offset] + 1;
    4638 again:
    4639                 mas->offset++;
    4640                 if (likely(mas->offset < data_end))
    4641                         mas->last = pivots[mas->offset];
    4642                 else
    4643                         mas->last = mas->max;
    4644         } else  {
    4645                 if (mas_next_node(mas, node, max)) {
    4646                         mas_rewalk(mas, save_point);
    4647                         goto retry;
    4648                 }
    4649 
    4650                 if (WARN_ON_ONCE(mas_is_none(mas))) {
    4651                         mas->node = MAS_OVERFLOW;

Should this set ->node even if set_overflow is false?

    4652                         return NULL;
--> 4653                         goto overflow;

Unreachable

    4654                 }
    4655 
    4656                 mas->offset = 0;
    4657                 mas->index = mas->min;
    4658                 node = mas_mn(mas);
    4659                 type = mte_node_type(mas->node);
    4660                 pivots = ma_pivots(node, type);
    4661                 mas->last = pivots[0];
    4662         }
    4663 
    4664         slots = ma_slots(node, type);
    4665         entry = mt_slot(mas->tree, slots, mas->offset);
    4666         if (unlikely(mas_rewalk_if_dead(mas, node, save_point)))
    4667                 goto retry;
    4668 
    4669         if (entry)
    4670                 return entry;
    4671 
    4672         if (!empty) {
    4673                 if (mas->last >= max)
    4674                         goto overflow;
    4675 
    4676                 mas->index = mas->last + 1;
    4677                 /* Node cannot end on NULL, so it's safe to short-cut here */
    4678                 goto again;
    4679         }
    4680 
    4681         return entry;
    4682 
    4683 overflow:
    4684         if (set_overflow)
    4685                 mas->node = MAS_OVERFLOW;
    4686         return NULL;
    4687 }

regards,
dan carpenter