maple_tree: Fix mas_spanning_rebalance() on insufficient data

Mike Rapoport contacted me off-list with a regression in running criu.
Periodic tests fail with an RCU stall during execution.  Although rare,
it is possible to hit this with other uses so this patch should be
backported to fix the regression.

An insufficient node was causing an out-of-bounds access on the node in
mas_leaf_max_gap().  The cause was the faulty detection of the new node
being a root node when overwriting many entries at the end of the tree.

Fix the detection of a new root and ensure there is sufficient data
prior to entering the spanning rebalance loop.

Add a testcase to the maple tree test suite for this issue.

Cc: Andrei Vagin <avagin@gmail.com>
Cc: usama.anjum@collabora.com
Reported-by: Mike Rapoport <rppt@kernel.org>
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index df352f6ccc240979f2fb03b9f096e4afc579a8cc..fe21bf276d91ce47149fcd0d22837fa737e7474d 100644 (file)
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -2989,7 +2989,9 @@ static int mas_spanning_rebalance(struct ma_state *mas,
        mast->free = &free;
        mast->destroy = &destroy;
        l_mas.node = r_mas.node = m_mas.node = MAS_NONE;
-       if (!(mast->orig_l->min && mast->orig_r->max == ULONG_MAX) &&
+
+       /* Check if this is not root and has sufficient data.  */
+       if (((mast->orig_l->min != 0) || (mast->orig_r->max != ULONG_MAX)) &&
            unlikely(mast->bn->b_end <= mt_min_slots[mast->bn->type]))
                mast_spanning_rebalance(mast);
 

diff --git a/lib/test_maple_tree.c b/lib/test_maple_tree.c
index f425f169ef08910149b6f845d770f73118dbef30..497fc93ccf9ecf550c0904c03bf20d707022a088 100644 (file)
--- a/lib/test_maple_tree.c
+++ b/lib/test_maple_tree.c
@@ -2498,6 +2498,25 @@ static noinline void check_dup(struct maple_tree *mt)
        }
 }
 
+static noinline void check_bnode_min_spanning(struct maple_tree *mt)
+{
+       int i = 50;
+       MA_STATE(mas, mt, 0, 0);
+
+       mt_set_non_kernel(9999);
+       mas_lock(&mas);
+       do {
+               mas_set_range(&mas, i*10, i*10+9);
+               mas_store(&mas, check_bnode_min_spanning);
+       } while (i--);
+
+       mas_set_range(&mas, 240, 509);
+       mas_store(&mas, NULL);
+       mas_unlock(&mas);
+       mas_destroy(&mas);
+       mt_set_non_kernel(0);
+}
+
 static DEFINE_MTREE(tree);
 static int maple_tree_seed(void)
 {
@@ -2742,6 +2761,10 @@ static int maple_tree_seed(void)
        check_dup(&tree);
        mtree_destroy(&tree);
 
+       mt_init_flags(&tree, MT_FLAGS_ALLOC_RANGE);
+       check_bnode_min_spanning(&tree);
+       mtree_destroy(&tree);
+
 #if defined(BENCH)
 skip:
 #endif