Subject: [PATCH v2 05/33] maple_tree: Fix write memory barrier of nodes once dead for RCU mode

From: Suren Baghdasaryan <[email-masked]>
Date: Fri, 27 Jan 2023 11:40:42 -0800

From: "Liam R. Howlett" <[email-masked]>

During the development of the maple tree, the strategy of freeing
multiple nodes changed and, in the process, the pivots were reused to
store pointers to dead nodes.  To ensure the readers see accurate
pivots, the writers need to mark the nodes as dead and call smp_wmb() to
ensure any readers can identify the node as dead before using the pivot
values.

There were two places where the old method of marking the node as dead
without smp_wmb() were being used, which resulted in RCU readers seeing
the wrong pivot value before seeing the node was dead.  Fix this race
condition by using mte_set_node_dead() which has the smp_wmb() call to
ensure the race is closed.

Add a WARN_ON() to the ma_free_rcu() call to ensure all nodes being
freed are marked as dead to ensure there are no other call paths besides
the two updated paths.

This is necessary for the RCU mode of the maple tree.

Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Liam R. Howlett <[email-masked]>
Signed-off-by: Suren Baghdasaryan <[email-masked]>
---
 lib/maple_tree.c                 |  7 +++++--
 tools/testing/radix-tree/maple.c | 16 ++++++++++++++++
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 75cce2d4d5da..49e399e8afaa 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -178,7 +178,7 @@ static void mt_free_rcu(struct rcu_head *head)
  */
 static void ma_free_rcu(struct maple_node *node)
 {
-	node->parent = ma_parent_ptr(node);
+	WARN_ON(node->parent != ma_parent_ptr(node));
 	call_rcu(&node->rcu, mt_free_rcu);
 }
 
@@ -1771,8 +1771,10 @@ static inline void mas_replace(struct ma_state *mas, bool advanced)
 		rcu_assign_pointer(slots[offset], mas->node);
 	}
 
-	if (!advanced)
+	if (!advanced) {
+		mte_set_node_dead(old_enode);
 		mas_free(mas, old_enode);
+	}
 }
 
 /*
@@ -4211,6 +4213,7 @@ static inline bool mas_wr_node_store(struct ma_wr_state *wr_mas)
 done:
 	mas_leaf_set_meta(mas, newnode, dst_pivots, maple_leaf_64, new_end);
 	if (in_rcu) {
+		mte_set_node_dead(mas->node);
 		mas->node = mt_mk_node(newnode, wr_mas->type);
 		mas_replace(mas, false);
 	} else {
diff --git a/tools/testing/radix-tree/maple.c b/tools/testing/radix-tree/maple.c
index 958ee9bdb316..4c89ff333f6f 100644
--- a/tools/testing/radix-tree/maple.c
+++ b/tools/testing/radix-tree/maple.c
@@ -108,6 +108,7 @@ static noinline void check_new_node(struct maple_tree *mt)
 	MT_BUG_ON(mt, mn->slot[1] != NULL);
 	MT_BUG_ON(mt, mas_allocated(&mas) != 0);
 
+	mn->parent = ma_parent_ptr(mn);
 	ma_free_rcu(mn);
 	mas.node = MAS_START;
 	mas_nomem(&mas, GFP_KERNEL);
@@ -160,6 +161,7 @@ static noinline void check_new_node(struct maple_tree *mt)
 		MT_BUG_ON(mt, mas_allocated(&mas) != i);
 		MT_BUG_ON(mt, !mn);
 		MT_BUG_ON(mt, not_empty(mn));
+		mn->parent = ma_parent_ptr(mn);
 		ma_free_rcu(mn);
 	}
 
@@ -192,6 +194,7 @@ static noinline void check_new_node(struct maple_tree *mt)
 		MT_BUG_ON(mt, not_empty(mn));
 		MT_BUG_ON(mt, mas_allocated(&mas) != i - 1);
 		MT_BUG_ON(mt, !mn);
+		mn->parent = ma_parent_ptr(mn);
 		ma_free_rcu(mn);
 	}
 
@@ -210,6 +213,7 @@ static noinline void check_new_node(struct maple_tree *mt)
 			mn = mas_pop_node(&mas);
 			MT_BUG_ON(mt, not_empty(mn));
 			MT_BUG_ON(mt, mas_allocated(&mas) != j - 1);
+			mn->parent = ma_parent_ptr(mn);
 			ma_free_rcu(mn);
 		}
 		MT_BUG_ON(mt, mas_allocated(&mas) != 0);
@@ -233,6 +237,7 @@ static noinline void check_new_node(struct maple_tree *mt)
 			MT_BUG_ON(mt, mas_allocated(&mas) != i - j);
 			mn = mas_pop_node(&mas);
 			MT_BUG_ON(mt, not_empty(mn));
+			mn->parent = ma_parent_ptr(mn);
 			ma_free_rcu(mn);
 			MT_BUG_ON(mt, mas_allocated(&mas) != i - j - 1);
 		}
@@ -269,6 +274,7 @@ static noinline void check_new_node(struct maple_tree *mt)
 			mn = mas_pop_node(&mas); /* get the next node. */
 			MT_BUG_ON(mt, mn == NULL);
 			MT_BUG_ON(mt, not_empty(mn));
+			mn->parent = ma_parent_ptr(mn);
 			ma_free_rcu(mn);
 		}
 		MT_BUG_ON(mt, mas_allocated(&mas) != 0);
@@ -294,6 +300,7 @@ static noinline void check_new_node(struct maple_tree *mt)
 			mn = mas_pop_node(&mas2); /* get the next node. */
 			MT_BUG_ON(mt, mn == NULL);
 			MT_BUG_ON(mt, not_empty(mn));
+			mn->parent = ma_parent_ptr(mn);
 			ma_free_rcu(mn);
 		}
 		MT_BUG_ON(mt, mas_allocated(&mas2) != 0);
@@ -334,10 +341,12 @@ static noinline void check_new_node(struct maple_tree *mt)
 	MT_BUG_ON(mt, mas_allocated(&mas) != MAPLE_ALLOC_SLOTS + 2);
 	mn = mas_pop_node(&mas);
 	MT_BUG_ON(mt, not_empty(mn));
+	mn->parent = ma_parent_ptr(mn);
 	ma_free_rcu(mn);
 	for (i = 1; i <= MAPLE_ALLOC_SLOTS + 1; i++) {
 		mn = mas_pop_node(&mas);
 		MT_BUG_ON(mt, not_empty(mn));
+		mn->parent = ma_parent_ptr(mn);
 		ma_free_rcu(mn);
 	}
 	MT_BUG_ON(mt, mas_allocated(&mas) != 0);
@@ -375,6 +384,7 @@ static noinline void check_new_node(struct maple_tree *mt)
 		mas_node_count(&mas, i); /* Request */
 		mas_nomem(&mas, GFP_KERNEL); /* Fill request */
 		mn = mas_pop_node(&mas); /* get the next node. */
+		mn->parent = ma_parent_ptr(mn);
 		ma_free_rcu(mn);
 		mas_destroy(&mas);
 
@@ -382,10 +392,13 @@ static noinline void check_new_node(struct maple_tree *mt)
 		mas_node_count(&mas, i); /* Request */
 		mas_nomem(&mas, GFP_KERNEL); /* Fill request */
 		mn = mas_pop_node(&mas); /* get the next node. */
+		mn->parent = ma_parent_ptr(mn);
 		ma_free_rcu(mn);
 		mn = mas_pop_node(&mas); /* get the next node. */
+		mn->parent = ma_parent_ptr(mn);
 		ma_free_rcu(mn);
 		mn = mas_pop_node(&mas); /* get the next node. */
+		mn->parent = ma_parent_ptr(mn);
 		ma_free_rcu(mn);
 		mas_destroy(&mas);
 	}
@@ -35369,6 +35382,7 @@ static noinline void check_prealloc(struct maple_tree *mt)
 	MT_BUG_ON(mt, allocated != 1 + height * 3);
 	mn = mas_pop_node(&mas);
 	MT_BUG_ON(mt, mas_allocated(&mas) != allocated - 1);
+	mn->parent = ma_parent_ptr(mn);
 	ma_free_rcu(mn);
 	MT_BUG_ON(mt, mas_preallocate(&mas, GFP_KERNEL) != 0);
 	mas_destroy(&mas);
@@ -35386,6 +35400,7 @@ static noinline void check_prealloc(struct maple_tree *mt)
 	mas_destroy(&mas);
 	allocated = mas_allocated(&mas);
 	MT_BUG_ON(mt, allocated != 0);
+	mn->parent = ma_parent_ptr(mn);
 	ma_free_rcu(mn);
 
 	MT_BUG_ON(mt, mas_preallocate(&mas, GFP_KERNEL) != 0);
@@ -35756,6 +35771,7 @@ void farmer_tests(void)
 	tree.ma_root = mt_mk_node(node, maple_leaf_64);
 	mt_dump(&tree);
 
+	node->parent = ma_parent_ptr(node);
 	ma_free_rcu(node);
 
 	/* Check things that will make lockdep angry */
-- 
2.39.1