[PATCH v6 2/2] sched/rt: Trying to push current task when target disable migrating

Schspa Shi
2022-07-12T15:13:03Z

When the task to push disable migration, retry to push the current
running task on this CPU away, instead doing nothing for this migrate
disabled task.

Signed-off-by: Schspa Shi <schspa@gmail.com>
---
kernel/sched/core.c | 13 ++++++++++++-
kernel/sched/rt.c | 6 ++++++
2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index da0bf6fe9ecdc..af90cc558b8ea 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2509,8 +2509,19 @@ int push_cpu_stop(void *arg)
if (p->sched_class->find_lock_rq)
lowest_rq = p->sched_class->find_lock_rq(p, rq);

- if (!lowest_rq)
+ if (!lowest_rq) {
+ /*
+ * The find_lock_rq function above could have released the rq
+ * lock and allow p to schedule and be preempted again, and
+ * that lowest_rq could be NULL because p now has the
+ * migrate_disable flag set and not because it could not find
+ * the lowest rq. So we must check task migration flag again.
+ */
+ if (unlikely(is_migration_disabled(p)))
+ p->migration_flags |= MDF_PUSH;
+
goto out_unlock;
+ }

// XXX validate p is still the highest prio task
if (task_rq(p) == rq) {
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 7bd3e6ecbe45e..e2d7b085a93d9 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2136,6 +2136,12 @@ static int push_rt_task(struct rq *rq, bool pull)
*/
task = pick_next_pushable_task(rq);
if (task == next_task) {
+ /*
+ * If next task has now disabled migrating, see if we
+ * can push the current task.
+ */
+ if (unlikely(is_migration_disabled(task)))
+ goto retry;
/*
* The task hasn't migrated, and is still the next
* eligible task, but we failed to find a run-queue
--
2.37.0