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Subject[PATCH v3 15/33] radix-tree: Move rcu_head into a union with private_list
Date
From: Matthew Wilcox <willy@infradead.org>

I want to be able to reference node->parent after freeing node.
Currently node->parent is in a union with rcu_head, so it is overwritten
when the node is put on the RCU list. We know that private_list is not
referenced after the node is freed, so it is safe for these two members
to share space.

Signed-off-by: Matthew Wilcox <willy@infradead.org>
---
include/linux/radix-tree.h | 14 ++++----------
lib/radix-tree.c | 1 +
2 files changed, 5 insertions(+), 10 deletions(-)

diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index 7444860..d04073a 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -85,18 +85,12 @@ struct radix_tree_node {
unsigned char offset; /* Slot offset in parent */
unsigned char count; /* Total entry count */
unsigned char exceptional; /* Exceptional entry count */
+ struct radix_tree_node *parent; /* Used when ascending tree */
+ void *private_data; /* For tree user */
union {
- struct {
- /* Used when ascending tree */
- struct radix_tree_node *parent;
- /* For tree user */
- void *private_data;
- };
- /* Used when freeing node */
- struct rcu_head rcu_head;
+ struct list_head private_list; /* For tree user */
+ struct rcu_head rcu_head; /* Used when freeing node */
};
- /* For tree user */
- struct list_head private_list;
void __rcu *slots[RADIX_TREE_MAP_SIZE];
unsigned long tags[RADIX_TREE_MAX_TAGS][RADIX_TREE_TAG_LONGS];
};
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index b329056..3f49417 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -324,6 +324,7 @@ static void radix_tree_node_rcu_free(struct rcu_head *head)
tag_clear(node, i, 0);

node->slots[0] = NULL;
+ INIT_LIST_HEAD(&node->private_list);

kmem_cache_free(radix_tree_node_cachep, node);
}
--
2.10.2
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