+ maple_tree-fix-write-memory-barrier-of-nodes-once-dead-for-rcu-mode.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: maple_tree: fix write memory barrier of nodes once dead for RCU mode
has been added to the -mm mm-unstable branch.  Its filename is
     maple_tree-fix-write-memory-barrier-of-nodes-once-dead-for-rcu-mode.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/maple_tree-fix-write-memory-barrier-of-nodes-once-dead-for-rcu-mode.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Subject: maple_tree: fix write memory barrier of nodes once dead for RCU mode
Date: Mon, 27 Feb 2023 09:36:04 -0800

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.

Link: https://lkml.kernel.org/r/20230227173632.3292573-6-surenb@google.com
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---


--- a/lib/maple_tree.c~maple_tree-fix-write-memory-barrier-of-nodes-once-dead-for-rcu-mode
+++ a/lib/maple_tree.c
@@ -185,7 +185,7 @@ static void mt_free_rcu(struct rcu_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);
 }
 
@@ -1778,8 +1778,10 @@ static inline void mas_replace(struct ma
 		rcu_assign_pointer(slots[offset], mas->node);
 	}
 
-	if (!advanced)
+	if (!advanced) {
+		mte_set_node_dead(old_enode);
 		mas_free(mas, old_enode);
+	}
 }
 
 /*
@@ -4218,6 +4220,7 @@ static inline bool mas_wr_node_store(str
 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 {
--- a/tools/testing/radix-tree/maple.c~maple_tree-fix-write-memory-barrier-of-nodes-once-dead-for-rcu-mode
+++ a/tools/testing/radix-tree/maple.c
@@ -108,6 +108,7 @@ static noinline void check_new_node(stru
 	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(stru
 		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(stru
 		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(stru
 			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(stru
 			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(stru
 			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(stru
 			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(stru
 	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(stru
 		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(stru
 		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(stru
 	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(stru
 	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 */
_

Patches currently in -mm which might be from Liam.Howlett@oracle.com are

mm-mprotect-fix-successful-vma_merge-of-next-in-do_mprotect_pkey.patch
maple_tree-be-more-cautious-about-dead-nodes.patch
maple_tree-detect-dead-nodes-in-mas_start.patch
maple_tree-fix-freeing-of-nodes-in-rcu-mode.patch
maple_tree-remove-extra-smp_wmb-from-mas_dead_leaves.patch
maple_tree-fix-write-memory-barrier-of-nodes-once-dead-for-rcu-mode.patch
maple_tree-add-smp_rmb-to-dead-node-detection.patch
maple_tree-add-rcu-lock-checking-to-rcu-callback-functions.patch
mm-enable-maple-tree-rcu-mode-by-default.patch