From: joe.korty@concurrent-rt.com
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Julia Cartwright <julia@ni.com>, <tglx@linutronix.de>,
<rostedt@goodmis.org>, <linux-rt-users@vger.kernel.org>,
<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH RT] sched/migrate_disable: fallback to preempt_disable() instead barrier()
Date: Thu, 5 Jul 2018 12:18:07 -0400 [thread overview]
Message-ID: <20180705161807.GA5800@zipoli.concurrent-rt.com> (raw)
In-Reply-To: <20180705155034.s6q2lsqc3o7srzwp@linutronix.de>
On Thu, Jul 05, 2018 at 05:50:34PM +0200, Sebastian Andrzej Siewior wrote:
> migrate_disable() does nothing !SMP && !RT. This is bad for two reasons:
> - The futex code relies on the fact migrate_disable() is part of spin_lock().
> There is a workaround for the !in_atomic() case in migrate_disable() which
> work-arounds the different ordering (non-atomic lock and atomic unlock).
>
> - we have a few instances where preempt_disable() is replaced with
> migrate_disable().
>
> For both cases it is bad if migrate_disable() ends up as barrier() instead of
> preempt_disable(). Let migrate_disable() fallback to preempt_disable().
>
> Cc: stable-rt@vger.kernel.org
> Reported-by: joe.korty@concurrent-rt.com
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
> include/linux/preempt.h | 4 ++--
> kernel/sched/core.c | 2 ++
> 2 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/preempt.h b/include/linux/preempt.h
> index 043e431a7e8e..d46688d521e6 100644
> --- a/include/linux/preempt.h
> +++ b/include/linux/preempt.h
> @@ -241,8 +241,8 @@ static inline int __migrate_disabled(struct task_struct *p)
> }
>
> #else
> -#define migrate_disable() barrier()
> -#define migrate_enable() barrier()
> +#define migrate_disable() preempt_disable()
> +#define migrate_enable() preempt_enable()
> static inline int __migrate_disabled(struct task_struct *p)
> {
> return 0;
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index ac3fb8495bd5..626a62218518 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -7326,6 +7326,7 @@ void migrate_disable(void)
> #endif
>
> p->migrate_disable++;
> + preempt_disable();
> }
> EXPORT_SYMBOL(migrate_disable);
>
> @@ -7349,6 +7350,7 @@ void migrate_enable(void)
>
> WARN_ON_ONCE(p->migrate_disable <= 0);
> p->migrate_disable--;
> + preempt_enable();
> }
> EXPORT_SYMBOL(migrate_enable);
> #endif
> --
> 2.18.0
Hi Sebastian,
I just verified that this fix does not work for my mix of
config options (smp && preempt && !rt).
Regards,
Joe
next prev parent reply other threads:[~2018-07-05 16:18 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-04 17:35 [PATCH RT] sample fix for splat in futex_[un]lock_pi for !rt joe.korty
2018-07-05 15:50 ` [PATCH RT] sched/migrate_disable: fallback to preempt_disable() instead barrier() Sebastian Andrzej Siewior
2018-07-05 16:18 ` joe.korty [this message]
2018-07-05 16:59 ` Sebastian Andrzej Siewior
2018-07-06 10:58 ` [PATCH RT v2] " Sebastian Andrzej Siewior
2018-07-06 19:05 ` joe.korty
2018-07-11 15:39 ` Sebastian Andrzej Siewior
2018-07-11 15:43 ` Steven Rostedt
2018-07-05 16:23 ` [PATCH RT] " Steven Rostedt
2018-07-05 16:38 ` Sebastian Andrzej Siewior
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