[PATCH 3/3] sched/deadline: fix inter- exclusive cpusets migrations

[Juri Lelli <juri.lelli@arm.com>]

Users can perform clustered scheduling using the cpuset facility.
After an exclusive cpuset is created, task migrations happen only
between CPUs belonging to the same cpuset. Inter- cpuset migrations
can only happen when the user requires so, moving a task between
different cpusets. This behaviour is broken in SCHED_DEADLINE, as
currently spurious inter- cpuset migration may happen without
user intervention.

This patch fix the problem (and shuffles the code a bit to improve
clarity).

Signed-off-by: Juri Lelli <juri.lelli@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@gmail.com>
Cc: Dario Faggioli <raistlin@linux.it>
Cc: Michael Trimarchi <michael@amarulasolutions.com>
Cc: Fabio Checconi <fchecconi@gmail.com>
Cc: linux-kernel@vger.kernel.org
---
 kernel/sched/cpudeadline.c | 4 +---
 kernel/sched/deadline.c    | 7 +++++++
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
index bd95963..539ca3c 100644
--- a/kernel/sched/cpudeadline.c
+++ b/kernel/sched/cpudeadline.c
@@ -107,9 +107,7 @@ int cpudl_find(struct cpudl *cp, struct task_struct *p,
 	int best_cpu = -1;
 	const struct sched_dl_entity *dl_se = &p->dl;
 
-	if (later_mask && cpumask_and(later_mask, cp->free_cpus,
-			&p->cpus_allowed) && cpumask_and(later_mask,
-			later_mask, cpu_active_mask)) {
+	if (later_mask && cpumask_and(later_mask, later_mask, cp->free_cpus)) {
 		best_cpu = cpumask_any(later_mask);
 		goto out;
 	} else if (cpumask_test_cpu(cpudl_maximum(cp), &p->cpus_allowed) &&
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 56cb157..2799441 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1169,6 +1169,13 @@ static int find_later_rq(struct task_struct *task)
 	if (task->nr_cpus_allowed == 1)
 		return -1;
 
+	/*
+	 * We have to consider system topology and task affinity
+	 * first, then we can look for a suitable cpu.
+	 */
+	cpumask_copy(later_mask, task_rq(task)->rd->span);
+	cpumask_and(later_mask, later_mask, cpu_active_mask);
+	cpumask_and(later_mask, later_mask, &task->cpus_allowed);
 	best_cpu = cpudl_find(&task_rq(task)->rd->cpudl,
 			task, later_mask);
 	if (best_cpu == -1)
-- 
2.1.0