From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Joe Korty <joe.korty@concurrent-rt.com>
Cc: Julia Cartwright <julia@ni.com>,
tglx@linutronix.de, rostedt@goodmis.org,
linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH RT] sched/migrate_disable: fallback to preempt_disable() instead barrier()
Date: Thu, 5 Jul 2018 17:50:34 +0200 [thread overview]
Message-ID: <20180705155034.s6q2lsqc3o7srzwp@linutronix.de> (raw)
In-Reply-To: <20180704173519.GA24614@zipoli.concurrent-rt.com>
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
next prev parent reply other threads:[~2018-07-05 15:50 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 ` Sebastian Andrzej Siewior [this message]
2018-07-05 16:18 ` [PATCH RT] sched/migrate_disable: fallback to preempt_disable() instead barrier() joe.korty
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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