linux-kernel - Re: [PATCH RT v3 3/5] sched: migrate_dis/enable: Use rt_invol

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Date:   Tue, 24 Sep 2019 13:21:55 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Scott Wood <swood@...hat.com>
Cc:     linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Paul E . McKenney" <paulmck@...ux.ibm.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Clark Williams <williams@...hat.com>
Subject: Re: [PATCH RT v3 3/5] sched: migrate_dis/enable: Use rt_invol_sleep

On 2019-09-23 19:52:33 [+0200], To Scott Wood wrote:

I made dis:

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 885a195dfbe02..25afa2bb1a2cf 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -308,7 +308,9 @@ void pin_current_cpu(void)
 	preempt_lazy_enable();
 	preempt_enable();
 
+	sleeping_lock_inc();
 	__read_rt_lock(cpuhp_pin);
+	sleeping_lock_dec();
 
 	preempt_disable();
 	preempt_lazy_disable();
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e1bdd7f9be054..63a6420d01053 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7388,6 +7388,7 @@ void migrate_enable(void)
 
 		WARN_ON(smp_processor_id() != task_cpu(p));
 		if (!cpumask_test_cpu(task_cpu(p), &p->cpus_mask)) {
+			struct task_struct *self = current;
 			const struct cpumask *cpu_valid_mask = cpu_active_mask;
 			struct migration_arg arg;
 			unsigned int dest_cpu;
@@ -7405,7 +7406,21 @@ void migrate_enable(void)
 			unpin_current_cpu();
 			preempt_lazy_enable();
 			preempt_enable();
+			rt_invol_sleep_inc();
+
+			raw_spin_lock_irq(&self->pi_lock);
+			self->saved_state = self->state;
+			__set_current_state_no_track(TASK_RUNNING);
+			raw_spin_unlock_irq(&self->pi_lock);
+
 			stop_one_cpu(task_cpu(p), migration_cpu_stop, &arg);
+
+			raw_spin_lock_irq(&self->pi_lock);
+			__set_current_state_no_track(self->saved_state);
+			self->saved_state = TASK_RUNNING;
+			raw_spin_unlock_irq(&self->pi_lock);
+
+			rt_invol_sleep_dec();
 			return;
 		}
 	}

I think we need to preserve the current state, otherwise we will lose
anything != TASK_RUNNING here. So the spin_lock() would preserve it
while waiting but the migrate_enable() will lose it if it needs to
change the CPU at the end.
I will try to prepare all commits for the next release before I release
so you can have a look first and yell if needed.

> > -Scott
 
Sebastian