1 files changed, 112 insertions, 0 deletions
diff --git a/debian/patches-rt/sched-migrate_enable-Use-stop_one_cpu_nowait.patch b/debian/patches-rt/sched-migrate_enable-Use-stop_one_cpu_nowait.patch
new file mode 100644
index 000000000..e75d0e306
--- /dev/null
+++ b/debian/patches-rt/sched-migrate_enable-Use-stop_one_cpu_nowait.patch
@@ -0,0 +1,112 @@
+From: Scott Wood <swood@redhat.com>
+Date: Sat, 12 Oct 2019 01:52:14 -0500
+Subject: [PATCH] sched: migrate_enable: Use stop_one_cpu_nowait()
+Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.4/older/patches-5.4.3-rt1.tar.xz
+
+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@redhat.com>
+[bigeasy: spin until the request has been processed]
+Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+---
+ include/linux/stop_machine.h |    2 ++
+ kernel/sched/core.c          |   27 +++++++++++++++++----------
+ kernel/stop_machine.c        |    7 +++++--
+ 3 files changed, 24 insertions(+), 12 deletions(-)
+
+--- 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);
+--- a/kernel/sched/core.c
++++ b/kernel/sched/core.c
+@@ -1536,6 +1536,7 @@ static struct rq *move_queued_task(struc
+ struct migration_arg {
+ 	struct task_struct *task;
+ 	int dest_cpu;
++	bool done;
+ };
+ 
+ /*
+@@ -1571,6 +1572,11 @@ 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
+@@ -1593,9 +1599,9 @@ 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);
+@@ -8144,7 +8150,8 @@ void migrate_enable(void)
+ 
+ 	WARN_ON(smp_processor_id() != cpu);
+ 	if (!is_cpu_allowed(p, cpu)) {
+-		struct migration_arg arg = { p };
++		struct migration_arg arg = { .task = p };
++		struct cpu_stop_work work;
+ 		struct rq_flags rf;
+ 
+ 		rq = task_rq_lock(p, &rf);
+@@ -8152,13 +8159,13 @@ void migrate_enable(void)
+ 		arg.dest_cpu = select_fallback_rq(cpu, p);
+ 		task_rq_unlock(rq, p, &rf);
+ 
+-		preempt_enable();
+-
+-		sleeping_lock_inc();
+-		stop_one_cpu(task_cpu(p), migration_cpu_stop, &arg);
+-		sleeping_lock_dec();
+-		return;
+-
++		stop_one_cpu_nowait(task_cpu(p), migration_cpu_stop,
++				    &arg, &work);
++		__schedule(true);
++		if (!work.disabled) {
++			while (!arg.done)
++				cpu_relax();
++		}
+ 	}
+ 
+ out:
+--- a/kernel/stop_machine.c
++++ b/kernel/stop_machine.c
+@@ -86,8 +86,11 @@ static bool cpu_stop_queue_work(unsigned
+ 	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);