maple_tree: fix mas_empty_area_rev() lower bound validation

mas_empty_area_rev() was not correctly validating the start of a gap
against the lower limit.  This could lead to the range starting lower than
the requested minimum.

Fix the issue by better validating a gap once one is found.

This commit also adds tests to the maple tree test suite for this issue
and tests the mas_empty_area() function for similar bound checking.

Link: https://lkml.kernel.org/r/20230111200136.1851322-1-Liam.Howlett@oracle.com
Link: https://bugzilla.kernel.org/show_bug.cgi?id=216911
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reported-by: <amanieu@gmail.com>
  Link: https://lore.kernel.org/linux-mm/0b9f5425-08d4-8013-aa4c-e620c3b10bb2@leemhuis.info/
Tested-by: Holger Hoffsttte <holger@applied-asynchrony.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 89 insertions, 0 deletions

diff --git a/lib/test_maple_tree.c b/lib/test_maple_tree.c
index 497fc93ccf9e..ec847bf4dcb4 100644
--- a/lib/test_maple_tree.c
+++ b/lib/test_maple_tree.c
@@ -2517,6 +2517,91 @@ static noinline void check_bnode_min_spanning(struct maple_tree *mt)
 	mt_set_non_kernel(0);
 }
 
+static noinline void check_empty_area_window(struct maple_tree *mt)
+{
+	unsigned long i, nr_entries = 20;
+	MA_STATE(mas, mt, 0, 0);
+
+	for (i = 1; i <= nr_entries; i++)
+		mtree_store_range(mt, i*10, i*10 + 9,
+				  xa_mk_value(i), GFP_KERNEL);
+
+	/* Create another hole besides the one at 0 */
+	mtree_store_range(mt, 160, 169, NULL, GFP_KERNEL);
+
+	/* Check lower bounds that don't fit */
+	rcu_read_lock();
+	MT_BUG_ON(mt, mas_empty_area_rev(&mas, 5, 90, 10) != -EBUSY);
+
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area_rev(&mas, 6, 90, 5) != -EBUSY);
+
+	/* Check lower bound that does fit */
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area_rev(&mas, 5, 90, 5) != 0);
+	MT_BUG_ON(mt, mas.index != 5);
+	MT_BUG_ON(mt, mas.last != 9);
+	rcu_read_unlock();
+
+	/* Check one gap that doesn't fit and one that does */
+	rcu_read_lock();
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area_rev(&mas, 5, 217, 9) != 0);
+	MT_BUG_ON(mt, mas.index != 161);
+	MT_BUG_ON(mt, mas.last != 169);
+
+	/* Check one gap that does fit above the min */
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area_rev(&mas, 100, 218, 3) != 0);
+	MT_BUG_ON(mt, mas.index != 216);
+	MT_BUG_ON(mt, mas.last != 218);
+
+	/* Check size that doesn't fit any gap */
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area_rev(&mas, 100, 218, 16) != -EBUSY);
+
+	/*
+	 * Check size that doesn't fit the lower end of the window but
+	 * does fit the gap
+	 */
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area_rev(&mas, 167, 200, 4) != -EBUSY);
+
+	/*
+	 * Check size that doesn't fit the upper end of the window but
+	 * does fit the gap
+	 */
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area_rev(&mas, 100, 162, 4) != -EBUSY);
+
+	/* Check mas_empty_area forward */
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area(&mas, 0, 100, 9) != 0);
+	MT_BUG_ON(mt, mas.index != 0);
+	MT_BUG_ON(mt, mas.last != 8);
+
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area(&mas, 0, 100, 4) != 0);
+	MT_BUG_ON(mt, mas.index != 0);
+	MT_BUG_ON(mt, mas.last != 3);
+
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area(&mas, 0, 100, 11) != -EBUSY);
+
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area(&mas, 5, 100, 6) != -EBUSY);
+
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area(&mas, 0, 8, 10) != -EBUSY);
+
+	mas_reset(&mas);
+	mas_empty_area(&mas, 100, 165, 3);
+
+	mas_reset(&mas);
+	MT_BUG_ON(mt, mas_empty_area(&mas, 100, 163, 6) != -EBUSY);
+	rcu_read_unlock();
+}
+
 static DEFINE_MTREE(tree);
 static int maple_tree_seed(void)
 {
@@ -2765,6 +2850,10 @@ static int maple_tree_seed(void)
 	check_bnode_min_spanning(&tree);
 	mtree_destroy(&tree);
 
+	mt_init_flags(&tree, MT_FLAGS_ALLOC_RANGE);
+	check_empty_area_window(&tree);
+	mtree_destroy(&tree);
+
 #if defined(BENCH)
 skip:
 #endif