diff --git a/Documentation/admin-guide/sysctl/net.rst b/Documentation/admin-guide/sysctl/net.rst
index c10530624f1e..3b2ad61995d4 100644
--- a/Documentation/admin-guide/sysctl/net.rst
+++ b/Documentation/admin-guide/sysctl/net.rst
@@ -594,6 +594,9 @@ Values:
 	  their sockets will only be able to connect within their own
 	  namespace.
 
+The first write to ``child_ns_mode`` locks its value. Subsequent writes of the
+same value succeed, but writing a different value returns ``-EBUSY``.
+
 Changing ``child_ns_mode`` only affects namespaces created after the change;
 it does not modify the current namespace or any existing children.