sched: Introduce dl_task_check_affinity() to check proposed affinity

In preparation for restricting the affinity of a task during execve()
on arm64, introduce a new dl_task_check_affinity() helper function to
give an indication as to whether the restricted mask is admissible for
a deadline task.

Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Link: https://lore.kernel.org/r/20210730112443.23245-10-will@kernel.org

1 files changed, 29 insertions, 17 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 6ee197049c9c..a22cc3c156ce 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7756,6 +7756,32 @@ out_unlock:
 	return retval;
 }
 
+#ifdef CONFIG_SMP
+int dl_task_check_affinity(struct task_struct *p, const struct cpumask *mask)
+{
+	int ret = 0;
+
+	/*
+	 * If the task isn't a deadline task or admission control is
+	 * disabled then we don't care about affinity changes.
+	 */
+	if (!task_has_dl_policy(p) || !dl_bandwidth_enabled())
+		return 0;
+
+	/*
+	 * Since bandwidth control happens on root_domain basis,
+	 * if admission test is enabled, we only admit -deadline
+	 * tasks allowed to run on all the CPUs in the task's
+	 * root_domain.
+	 */
+	rcu_read_lock();
+	if (!cpumask_subset(task_rq(p)->rd->span, mask))
+		ret = -EBUSY;
+	rcu_read_unlock();
+	return ret;
+}
+#endif
+
 static int
 __sched_setaffinity(struct task_struct *p, const struct cpumask *mask)
 {
@@ -7773,23 +7799,9 @@ __sched_setaffinity(struct task_struct *p, const struct cpumask *mask)
 	cpuset_cpus_allowed(p, cpus_allowed);
 	cpumask_and(new_mask, mask, cpus_allowed);
 
-	/*
-	 * Since bandwidth control happens on root_domain basis,
-	 * if admission test is enabled, we only admit -deadline
-	 * tasks allowed to run on all the CPUs in the task's
-	 * root_domain.
-	 */
-#ifdef CONFIG_SMP
-	if (task_has_dl_policy(p) && dl_bandwidth_enabled()) {
-		rcu_read_lock();
-		if (!cpumask_subset(task_rq(p)->rd->span, new_mask)) {
-			retval = -EBUSY;
-			rcu_read_unlock();
-			goto out_free_new_mask;
-		}
-		rcu_read_unlock();
-	}
-#endif
+	retval = dl_task_check_affinity(p, new_mask);
+	if (retval)
+		goto out_free_new_mask;
 again:
 	retval = __set_cpus_allowed_ptr(p, new_mask, SCA_CHECK | SCA_USER);
 	if (retval)