test_maple_tree: test exhausted upper limit of mtree_alloc_cyclic()

When the upper bound of the search is exhausted, the maple state may be
returned in an error state of -EBUSY.  This means maple state needs to be
reset before the second search in mas_alloc_cylic() to ensure the search
happens.  This test ensures the issue is not recreated.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Liam R. Howlett <[email protected]>
Reviewed-by: Yang Erkun <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Chuck Lever <[email protected]> says:
Signed-off-by: Andrew Morton <[email protected]>

Author: howlett

lib/test_maple_tree.c

@@ -3738,6 +3738,34 @@ static noinline void __init alloc_cyclic_testing(struct maple_tree *mt)
 	}
 
 	mtree_destroy(mt);
+
+	/*
+	 * Issue with reverse search was discovered
+	 * https://lore.kernel.org/all/[email protected]/
+	 * Exhausting the allocation area and forcing the search to wrap needs a
+	 * mas_reset() in mas_alloc_cyclic().
+	 */
+	next = 0;
+	mt_init_flags(mt, MT_FLAGS_ALLOC_RANGE);
+	for (int i = 0; i < 1023; i++) {
+		mtree_alloc_cyclic(mt, &location, mt, 2, 1024, &next, GFP_KERNEL);
+		MT_BUG_ON(mt, i != location - 2);
+		MT_BUG_ON(mt, i != next - 3);
+		MT_BUG_ON(mt, mtree_load(mt, location) != mt);
+	}
+	mtree_erase(mt, 123);
+	MT_BUG_ON(mt, mtree_load(mt, 123) != NULL);
+	mtree_alloc_cyclic(mt, &location, mt, 2, 1024, &next, GFP_KERNEL);
+	MT_BUG_ON(mt, 123 != location);
+	MT_BUG_ON(mt, 124 != next);
+	MT_BUG_ON(mt, mtree_load(mt, location) != mt);
+	mtree_erase(mt, 100);
+	mtree_alloc_cyclic(mt, &location, mt, 2, 1024, &next, GFP_KERNEL);
+	MT_BUG_ON(mt, 100 != location);
+	MT_BUG_ON(mt, 101 != next);
+	MT_BUG_ON(mt, mtree_load(mt, location) != mt);
+	mtree_destroy(mt);
+
 	/* Overflow test */
 	next = ULONG_MAX - 1;
 	ret = mtree_alloc_cyclic(mt, &location, mt, 2, ULONG_MAX, &next, GFP_KERNEL);