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

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Date:   Tue, 12 Jul 2022 23:05:06 +0800
From:   Schspa Shi <schspa@...il.com>
To:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com
Cc:     linux-kernel@...r.kernel.org, zhaohui.shi@...izon.ai,
        Schspa Shi <schspa@...il.com>
Subject: [PATCH v6 2/2] sched/rt: Trying to push current task when target disable migrating

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@...il.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