dm thin: fix memory leak in process_prepared_mapping error paths

Fix memory leak in process_prepared_mapping by always freeing
the dm_thin_new_mapping structs from the mapping_pool mempool on
the error paths.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-thin.c

@@ -870,7 +870,7 @@ static void process_prepared_mapping(struct dm_thin_new_mapping *m)
 
 	if (m->err) {
 		cell_error(m->cell);
-		return;
+		goto out;
 	}
 
 	/*
@@ -882,7 +882,7 @@ static void process_prepared_mapping(struct dm_thin_new_mapping *m)
 	if (r) {
 		DMERR("dm_thin_insert_block() failed");
 		cell_error(m->cell);
-		return;
+		goto out;
 	}
 
 	/*
@@ -897,6 +897,7 @@ static void process_prepared_mapping(struct dm_thin_new_mapping *m)
 	} else
 		cell_defer(tc, m->cell, m->data_block);
 
+out:
 	list_del(&m->list);
 	mempool_free(m, tc->pool->mapping_pool);
 }