linux-kernel - [PATCH RT 18/23] sched: migrate_enable: Use stop_one_cpu

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Date:   Thu, 27 Feb 2020 08:33:29 -0600
From:   zanussi@...nel.org
To:     LKML <linux-kernel@...r.kernel.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Carsten Emde <C.Emde@...dl.org>,
        John Kacur <jkacur@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Daniel Wagner <wagi@...om.org>,
        Tom Zanussi <zanussi@...nel.org>
Subject: [PATCH RT 18/23] sched: migrate_enable: Use stop_one_cpu_nowait()

From: Scott Wood <swood@...hat.com>

v4.14.170-rt75-rc2 stable review patch.
If anyone has any objections, please let me know.

-----------


[ Upstream commit 6b39a1fa8c53cae08dc03afdae193b7d3a78a173 ]

migrate_enable() can be called with current->state != TASK_RUNNING.
Avoid clobbering the existing state by using stop_one_cpu_nowait().
Since we're stopping the current cpu, we know that we won't get
past __schedule() until migration_cpu_stop() has run (at least up to
the point of migrating us to another cpu).

Signed-off-by: Scott Wood <swood@...hat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Tom Zanussi <zanussi@...nel.org>

 Conflicts:
	kernel/sched/core.c
---
 include/linux/stop_machine.h |  2 ++
 kernel/sched/core.c          | 23 +++++++++++++----------
 kernel/stop_machine.c        |  7 +++++--
 3 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/include/linux/stop_machine.h b/include/linux/stop_machine.h
index 6d3635c86dbe..82fc686ddd9e 100644
--- a/include/linux/stop_machine.h
+++ b/include/linux/stop_machine.h
@@ -26,6 +26,8 @@ struct cpu_stop_work {
 	cpu_stop_fn_t		fn;
 	void			*arg;
 	struct cpu_stop_done	*done;
+	/* Did not run due to disabled stopper; for nowait debug checks */
+	bool			disabled;
 };
 
 int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 6066dc7bd7b2..ceddb1e27caf 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1025,6 +1025,7 @@ static struct rq *move_queued_task(struct rq *rq, struct rq_flags *rf,
 struct migration_arg {
 	struct task_struct *task;
 	int dest_cpu;
+	bool done;
 };
 
 /*
@@ -1060,6 +1061,11 @@ static int migration_cpu_stop(void *data)
 	struct task_struct *p = arg->task;
 	struct rq *rq = this_rq();
 	struct rq_flags rf;
+	int dest_cpu = arg->dest_cpu;
+
+	/* We don't look at arg after this point. */
+	smp_mb();
+	arg->done = true;
 
 	/*
 	 * The original target CPU might have gone down and we might
@@ -1082,9 +1088,9 @@ static int migration_cpu_stop(void *data)
 	 */
 	if (task_rq(p) == rq) {
 		if (task_on_rq_queued(p))
-			rq = __migrate_task(rq, &rf, p, arg->dest_cpu);
+			rq = __migrate_task(rq, &rf, p, dest_cpu);
 		else
-			p->wake_cpu = arg->dest_cpu;
+			p->wake_cpu = dest_cpu;
 	}
 	rq_unlock(rq, &rf);
 	raw_spin_unlock(&p->pi_lock);
@@ -6995,6 +7001,7 @@ void migrate_enable(void)
 	WARN_ON(smp_processor_id() != cpu);
 	if (!is_cpu_allowed(p, cpu)) {
 		struct migration_arg arg = { p };
+		struct cpu_stop_work work;
 		struct rq_flags rf;
 
 		rq = task_rq_lock(p, &rf);
@@ -7002,15 +7009,11 @@ void migrate_enable(void)
 		arg.dest_cpu = select_fallback_rq(cpu, p);
 		task_rq_unlock(rq, p, &rf);
 
-		preempt_lazy_enable();
-		preempt_enable();
-
-		sleeping_lock_inc();
-		stop_one_cpu(task_cpu(p), migration_cpu_stop, &arg);
-		sleeping_lock_dec();
+		stop_one_cpu_nowait(task_cpu(p), migration_cpu_stop,
+				    &arg, &work);
 		tlb_migrate_finish(p->mm);
-
-		return;
+		__schedule(true);
+		WARN_ON_ONCE(!arg.done && !work.disabled);
 	}
 
 out:
diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 56f2f2e01229..0e2fc590ba88 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -86,8 +86,11 @@ static bool cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
 	enabled = stopper->enabled;
 	if (enabled)
 		__cpu_stop_queue_work(stopper, work, &wakeq);
-	else if (work->done)
-		cpu_stop_signal_done(work->done);
+	else {
+		work->disabled = true;
+		if (work->done)
+			cpu_stop_signal_done(work->done);
+	}
 	raw_spin_unlock_irqrestore(&stopper->lock, flags);
 
 	wake_up_q(&wakeq);
-- 
2.14.1