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-rw-r--r--fs/btrfs/delayed-inode.c45
1 files changed, 34 insertions, 11 deletions
diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
index 5d73f79ded8b..056276101c63 100644
--- a/fs/btrfs/delayed-inode.c
+++ b/fs/btrfs/delayed-inode.c
@@ -87,6 +87,7 @@ static struct btrfs_delayed_node *btrfs_get_delayed_node(
spin_lock(&root->inode_lock);
node = radix_tree_lookup(&root->delayed_nodes_tree, ino);
+
if (node) {
if (btrfs_inode->delayed_node) {
refcount_inc(&node->refs); /* can be accessed */
@@ -94,9 +95,30 @@ static struct btrfs_delayed_node *btrfs_get_delayed_node(
spin_unlock(&root->inode_lock);
return node;
}
- btrfs_inode->delayed_node = node;
- /* can be accessed and cached in the inode */
- refcount_add(2, &node->refs);
+
+ /*
+ * It's possible that we're racing into the middle of removing
+ * this node from the radix tree. In this case, the refcount
+ * was zero and it should never go back to one. Just return
+ * NULL like it was never in the radix at all; our release
+ * function is in the process of removing it.
+ *
+ * Some implementations of refcount_inc refuse to bump the
+ * refcount once it has hit zero. If we don't do this dance
+ * here, refcount_inc() may decide to just WARN_ONCE() instead
+ * of actually bumping the refcount.
+ *
+ * If this node is properly in the radix, we want to bump the
+ * refcount twice, once for the inode and once for this get
+ * operation.
+ */
+ if (refcount_inc_not_zero(&node->refs)) {
+ refcount_inc(&node->refs);
+ btrfs_inode->delayed_node = node;
+ } else {
+ node = NULL;
+ }
+
spin_unlock(&root->inode_lock);
return node;
}
@@ -254,17 +276,18 @@ static void __btrfs_release_delayed_node(
mutex_unlock(&delayed_node->mutex);
if (refcount_dec_and_test(&delayed_node->refs)) {
- bool free = false;
struct btrfs_root *root = delayed_node->root;
+
spin_lock(&root->inode_lock);
- if (refcount_read(&delayed_node->refs) == 0) {
- radix_tree_delete(&root->delayed_nodes_tree,
- delayed_node->inode_id);
- free = true;
- }
+ /*
+ * Once our refcount goes to zero, nobody is allowed to bump it
+ * back up. We can delete it now.
+ */
+ ASSERT(refcount_read(&delayed_node->refs) == 0);
+ radix_tree_delete(&root->delayed_nodes_tree,
+ delayed_node->inode_id);
spin_unlock(&root->inode_lock);
- if (free)
- kmem_cache_free(delayed_node_cache, delayed_node);
+ kmem_cache_free(delayed_node_cache, delayed_node);
}
}