task/cgroup: correct a regression in cpuset management

The addition of the default slurm cg with the cpuset subsystem was
incomplete preventing from having a working solution. The contents
of cpuset.cpus and cpuset.mems were not replicated from the parent
resulting in "No space left on device" errors when trying to add
tasks to the step cg.

src/plugins/task/cgroup/task_cgroup_cpuset.c

@@ -168,6 +168,7 @@ extern int task_cgroup_cpuset_create(slurmd_job_t *job)
 	size_t cpus_size;
 
 	char* slurm_cgpath ;
+	xcgroup_t slurm_cg;
 
 	/* create slurm root cg in this cg namespace */
 	slurm_cgpath = task_cgroup_create_slurm_cg(&cpuset_ns);
@@ -175,6 +176,25 @@ extern int task_cgroup_cpuset_create(slurmd_job_t *job)
 		return SLURM_ERROR;
 	}
 
+	/* check that this cgroup has cpus allowed or initialize them */
+	if (xcgroup_load(&cpuset_ns,&slurm_cg,slurm_cgpath)
+	    != XCGROUP_SUCCESS) {
+		error("task/cgroup: unable to load slurm cpuset xcgroup");
+		xfree(slurm_cgpath);
+		return SLURM_ERROR;
+	}
+	rc = xcgroup_get_param(&slurm_cg,"cpuset.cpus",&cpus,&cpus_size);
+	if (rc != XCGROUP_SUCCESS || cpus_size == 1) {
+		/* initialize the cpusets as it was inexistant */
+		if (_xcgroup_cpuset_init(&slurm_cg) !=
+		    XCGROUP_SUCCESS) {
+			xfree(slurm_cgpath);
+			xcgroup_destroy(&slurm_cg);
+			return SLURM_ERROR;
+		}
+	}
+	xfree(cpus);
+
 	/* build user cgroup relative path if not set (should not be) */
 	if (*user_cgroup_path == '\0') {
 		if (snprintf(user_cgroup_path, PATH_MAX,