* Description: Returns the cpumask_var_t cpus_allowed of the cpuset
* attached to the specified @tsk. Guaranteed to return some non-empty
* subset of cpu_online_mask, even if this means going outside the
- * tasks cpuset.
+ * tasks cpuset, except when the task is in the top cpuset.
**/
void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
{
unsigned long flags;
+ struct cpuset *cs;
spin_lock_irqsave(&callback_lock, flags);
- guarantee_online_cpus(tsk, pmask);
+ rcu_read_lock();
+
+ cs = task_cs(tsk);
+ if (cs != &top_cpuset)
+ guarantee_online_cpus(tsk, pmask);
+ /*
+ * Tasks in the top cpuset won't get update to their cpumasks
+ * when a hotplug online/offline event happens. So we include all
+ * offline cpus in the allowed cpu list.
+ */
+ if ((cs == &top_cpuset) || cpumask_empty(pmask)) {
+ const struct cpumask *possible_mask = task_cpu_possible_mask(tsk);
+
+ /*
+ * We first exclude cpus allocated to partitions. If there is no
+ * allowable online cpu left, we fall back to all possible cpus.
+ */
+ cpumask_andnot(pmask, possible_mask, top_cpuset.subparts_cpus);
+ if (!cpumask_intersects(pmask, cpu_online_mask))
+ cpumask_copy(pmask, possible_mask);
+ }
+
+ rcu_read_unlock();
spin_unlock_irqrestore(&callback_lock, flags);
}