[bug report] maple_tree: add MAS_UNDERFLOW and MAS_OVERFLOW states

[Liam R. Howlett]

* Dan Carpenter <dan.carpenter at linaro.org> [230927 08:42]:
> 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 {
...
>     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?

Yes.  Perhaps a comment should be added to clarify.

The overflow condition is the only reason mas_next_node() will return
MAS_NONE.  The only reason to keep the mas->node active is to avoid
re-walking the tree, but in this case mas->node == MAS_NONE, so the
re-walk will occur.  Setting this to MAS_OVERFLOW will fix the
inconsistency in what the user expects to happen with the maple state in
later calls, so it is the correct thing to do here.

> 
>     4652                         return NULL;
> --> 4653                         goto overflow;
> 
> Unreachable
> 
>     4654                 }
...

Thanks for the bug report.  That goto should be removed.

Regards,
Liam