Silence lxc-unshare warning when removing cgroup

src/lxc/cgroup.c

@@ -82,6 +82,13 @@ static int get_cgroup_mount(const char *subsystem, char *mnt)
 	return -1;
 }
 
+int lxc_ns_is_mounted(void)
+{
+	static char        buf[MAXPATHLEN];
+
+	return (get_cgroup_mount("ns", buf) == 0);
+}
+
 static int get_cgroup_flags(struct mntent *mntent)
 {
 	int flags = 0;

src/lxc/cgroup.h

@@ -30,4 +30,5 @@ int lxc_cgroup_create(const char *name, pid_t pid);
 int lxc_cgroup_destroy(const char *name);
 int lxc_cgroup_path_get(char **path, const char *subsystem, const char *name);
 int lxc_cgroup_nrtasks(const char *name);
+int lxc_ns_is_mounted(void);
 #endif

src/lxc/lxc_unshare.c

@@ -210,12 +210,14 @@ int main(int argc, char *argv[])
 		return -1;
 	}
 
-	if (asprintf(&pid_name, "%d", pid) == -1) {
-		ERROR("pid_name: failed to allocate memory");
-		return -1;
+	if (lxc_ns_is_mounted()) {
+		if (asprintf(&pid_name, "%d", pid) == -1) {
+			ERROR("pid_name: failed to allocate memory");
+			return -1;
+		}
+		lxc_cgroup_destroy(pid_name);
+		free(pid_name);
 	}
-	lxc_cgroup_destroy(pid_name);
-	free(pid_name);
 
 	return  lxc_error_set_and_log(pid, status);
 }