dax: make use of ->free_inode()

we might want to drop ->destroy_inode() there - it's used only for
WARN_ON() now, and AFAICS that could be moved to ->evict_inode()
if we had one...
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

drivers/dax/super.c

@@ -412,11 +412,9 @@ static struct dax_device *to_dax_dev(struct inode *inode)
 	return container_of(inode, struct dax_device, inode);
 }
 
-static void dax_i_callback(struct rcu_head *head)
+static void dax_free_inode(struct inode *inode)
 {
-	struct inode *inode = container_of(head, struct inode, i_rcu);
 	struct dax_device *dax_dev = to_dax_dev(inode);
-
 	kfree(dax_dev->host);
 	dax_dev->host = NULL;
 	if (inode->i_rdev)
@@ -427,16 +425,15 @@ static void dax_i_callback(struct rcu_head *head)
 static void dax_destroy_inode(struct inode *inode)
 {
 	struct dax_device *dax_dev = to_dax_dev(inode);
-
 	WARN_ONCE(test_bit(DAXDEV_ALIVE, &dax_dev->flags),
 			"kill_dax() must be called before final iput()\n");
-	call_rcu(&inode->i_rcu, dax_i_callback);
 }
 
 static const struct super_operations dax_sops = {
 	.statfs = simple_statfs,
 	.alloc_inode = dax_alloc_inode,
 	.destroy_inode = dax_destroy_inode,
+	.free_inode = dax_free_inode,
 	.drop_inode = generic_delete_inode,
 };