From: Scott Wood <swood@redhat.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org,
"Paul E . McKenney" <paulmck@linux.ibm.com>,
Joel Fernandes <joel@joelfernandes.org>,
Thomas Gleixner <tglx@linutronix.de>,
Steven Rostedt <rostedt@goodmis.org>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Clark Williams <williams@redhat.com>
Subject: Re: [PATCH RT v3 3/5] sched: migrate_dis/enable: Use rt_invol_sleep
Date: Tue, 24 Sep 2019 08:53:43 -0500 [thread overview]
Message-ID: <55dc19fcc44b2e658b71f68206306c8310335564.camel@redhat.com> (raw)
In-Reply-To: <20190924112155.rxeyksetgqmer3pg@linutronix.de>
On Tue, 2019-09-24 at 13:21 +0200, Sebastian Andrzej Siewior wrote:
> 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.
As I pointed out in the "[PATCH RT 6/8] sched: migrate_enable: Set state to
TASK_RUNNING" discussion, we can get here inside the rtmutex code (e.g. from
debug_rt_mutex_print_deadlock) where saved_state is already holding
something -- plus, the waker won't have WF_LOCK_SLEEPER and therefore
saved_state will get cleared anyway.
-Scott
next prev parent reply other threads:[~2019-09-24 13:54 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-11 16:57 [PATCH RT v3 0/5] RCU fixes Scott Wood
2019-09-11 16:57 ` [PATCH RT v3 1/5] rcu: Acquire RCU lock when disabling BHs Scott Wood
2019-09-12 22:09 ` Joel Fernandes
2019-09-17 7:44 ` Sebastian Andrzej Siewior
2019-09-17 14:06 ` Scott Wood
2019-09-17 14:42 ` Sebastian Andrzej Siewior
2019-09-17 16:12 ` Scott Wood
2019-09-23 16:41 ` Sebastian Andrzej Siewior
2019-09-11 16:57 ` [PATCH RT v3 2/5] sched: Rename sleeping_lock to rt_invol_sleep Scott Wood
2019-09-17 7:52 ` Sebastian Andrzej Siewior
2019-09-11 16:57 ` [PATCH RT v3 3/5] sched: migrate_dis/enable: Use rt_invol_sleep Scott Wood
2019-09-17 7:59 ` Sebastian Andrzej Siewior
2019-09-17 14:06 ` Scott Wood
2019-09-23 16:59 ` Scott Wood
2019-09-23 17:52 ` Sebastian Andrzej Siewior
2019-09-24 11:21 ` Sebastian Andrzej Siewior
2019-09-24 13:53 ` Scott Wood [this message]
2019-09-24 15:25 ` Sebastian Andrzej Siewior
2019-09-24 15:47 ` Scott Wood
2019-09-24 16:05 ` Sebastian Andrzej Siewior
2019-09-24 16:35 ` Scott Wood
2019-10-04 16:45 ` Sebastian Andrzej Siewior
2019-09-11 16:57 ` [PATCH RT v3 4/5] rcu: Disable use_softirq on PREEMPT_RT Scott Wood
2019-09-12 21:38 ` Joel Fernandes
2019-09-12 22:19 ` Joel Fernandes
2019-09-17 9:31 ` Sebastian Andrzej Siewior
2019-09-17 14:08 ` Scott Wood
2019-09-11 16:57 ` [PATCH RT v3 5/5] rcutorture: Avoid problematic critical section nesting on RT Scott Wood
2019-09-12 22:17 ` Joel Fernandes
2019-09-16 16:55 ` Scott Wood
2019-09-17 10:07 ` Sebastian Andrzej Siewior
2019-09-17 14:36 ` Scott Wood
2019-09-17 14:50 ` Sebastian Andrzej Siewior
2019-09-17 16:32 ` Scott Wood
2019-09-23 16:25 ` Sebastian Andrzej Siewior
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