linux-kernel - [PATCH v8 2/2] sched/rt: Trying to push current task when target disable migrating

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Date:   Mon, 29 Aug 2022 01:03:03 +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 v8 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.

CC: Valentin Schneider <vschneid@...hat.com>
Signed-off-by: Schspa Shi <schspa@...il.com>
Reviewed-by: Steven Rostedt (Google) <rostedt@...dmis.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>
---
 kernel/sched/core.c     | 13 ++++++++++++-
 kernel/sched/deadline.c |  9 +++++++++
 kernel/sched/rt.c       |  8 ++++++++
 3 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ee28253c9ac0c..056b336c29e70 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2503,8 +2503,19 @@ 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/deadline.c b/kernel/sched/deadline.c
index e7eea6cde5cb9..c8055b978dbc3 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -2340,6 +2340,15 @@ static int push_dl_task(struct rq *rq)
 		 */
 		task = pick_next_pushable_dl_task(rq);
 		if (task == next_task) {
+			/*
+			 * If next task has now disabled migrating, see if we
+			 * can do resched_curr().
+			 */
+			if (unlikely(is_migration_disabled(task))) {
+				put_task_struct(next_task);
+				goto retry;
+			}
+
 			/*
 			 * The task is still there. We don't try
 			 * again, some other CPU will pull it when ready.
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 57e8cd5c9c267..381ec05eb2701 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2139,6 +2139,14 @@ 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))) {
+				put_task_struct(next_task);
+				goto retry;
+			}
 			/*
 			 * The task hasn't migrated, and is still the next
 			 * eligible task, but we failed to find a run-queue
-- 
2.37.2