maple_tree: make maple state reusable after mas_empty_area()

Make mas->min and mas->max point to a node range instead of a leaf entry
range.  This allows mas to still be usable after mas_empty_area() returns.
Users would get unexpected results from other operations on the maple
state after calling the affected function.

For example, x86 MAP_32BIT mmap() acts as if there is no suitable gap when
there should be one.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 54a611b ("Maple Tree: add new data structure")
Signed-off-by: Peng Zhang <[email protected]>
Reported-by: "Edgecombe, Rick P" <[email protected]>
Reported-by: Tad <[email protected]>
Reported-by: Michael Keyes <[email protected]>
  Link: https://lore.kernel.org/linux-mm/[email protected]/
  Link: https://lore.kernel.org/linux-mm/[email protected]/
Reviewed-by: Liam R. Howlett <[email protected]>
Tested-by: Rick Edgecombe <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Peng Zhang

lib/maple_tree.c

@@ -5317,15 +5317,9 @@ int mas_empty_area(struct ma_state *mas, unsigned long min,
 
 	mt = mte_node_type(mas->node);
 	pivots = ma_pivots(mas_mn(mas), mt);
-	if (offset)
-		mas->min = pivots[offset - 1] + 1;
-
-	if (offset < mt_pivots[mt])
-		mas->max = pivots[offset];
-
-	if (mas->index < mas->min)
-		mas->index = mas->min;
-
+	min = mas_safe_min(mas, pivots, offset);
+	if (mas->index < min)
+		mas->index = min;
 	mas->last = mas->index + size - 1;
 	return 0;
 }