snip

.

.

.

  
+#ifdef CONFIG_PROC_FS
+static inline void pidns_proc_lock(struct pid_namespace *pid_ns)
+{
+	down_write(&pid_ns->rw_proc_mounts);
+}
+
+static inline void pidns_proc_unlock(struct pid_namespace *pid_ns)
+{
+	up_write(&pid_ns->rw_proc_mounts);
+}
+
+static inline void pidns_proc_lock_shared(struct pid_namespace *pid_ns)
+{
+	down_read(&pid_ns->rw_proc_mounts);
+}
+
+static inline void pidns_proc_unlock_shared(struct pid_namespace *pid_ns)
+{
+	up_read(&pid_ns->rw_proc_mounts);
+}
+#else /* !CONFIG_PROC_FS */
+

Apologies for my newbie question. I couldn't help but notice all these 
function calls are assuming that the parameter struct pid_namespace 
*pid_ns will never be NULL.  Is that a good assumption?

I don't have the background in this code to answer on my own, but I 
thought I'd raise the question.

Thanks,
Jay