Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Schspa Shi <schspa@gmail.com>
To:     mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com,
        vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
        rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
        bristot@redhat.com, vschneid@redhat.com
Cc:     linux-kernel@vger.kernel.org, zhaohui.shi@horizon.ai,
        Schspa Shi <schspa@gmail.com>
Subject: [PATCH v6 2/2] sched/rt: Trying to push current task when target disable migrating
Date:   Tue, 12 Jul 2022 23:05:06 +0800
Message-Id: <20220712150506.632304-2-schspa@gmail.com>
In-Reply-To: <20220712150506.632304-1-schspa@gmail.com>
References: <20220712150506.632304-1-schspa@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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