From: Mike Galbraith <umgwanakikbuti@gmail.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
linux-rt-users@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH RT 4/6] rt/locking: Reenable migration accross schedule
Date: Sun, 20 Mar 2016 09:43:45 +0100 [thread overview]
Message-ID: <1458463425.3908.5.camel@gmail.com> (raw)
In-Reply-To: <1455318168-7125-4-git-send-email-bigeasy@linutronix.de>
On Sat, 2016-02-13 at 00:02 +0100, Sebastian Andrzej Siewior wrote:
> From: Thomas Gleixner <tglx@linutronix.de>
>
> We currently disable migration across lock acquisition. That includes the part
> where we block on the lock and schedule out. We cannot disable migration after
> taking the lock as that would cause a possible lock inversion.
>
> But we can be smart and enable migration when we block and schedule out. That
> allows the scheduler to place the task freely at least if this is the first
> migrate disable level. For nested locking this does not help at all.
I met a problem while testing shiny new hotplug machinery.
rt/locking: Fix rt_spin_lock_slowlock() vs hotplug migrate_disable() bug
migrate_disable() -> pin_current_cpu() -> hotplug_lock() leads to..
BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on));
..so let's call migrate_disable() after we acquire the lock instead.
Fixes: e24b142cfb4a rt/locking: Reenable migration accross schedule
Signed-off-by: Mike Galbraith <umgwanakikbuti@gmailo.com>
---
kernel/locking/rtmutex.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1011,7 +1011,7 @@ static void noinline __sched rt_spin_lo
struct task_struct *lock_owner, *self = current;
struct rt_mutex_waiter waiter, *top_waiter;
unsigned long flags;
- int ret;
+ bool mg_disable = false;
rt_mutex_init_waiter(&waiter, true);
@@ -1035,8 +1035,7 @@ static void noinline __sched rt_spin_lo
__set_current_state_no_track(TASK_UNINTERRUPTIBLE);
raw_spin_unlock(&self->pi_lock);
- ret = task_blocks_on_rt_mutex(lock, &waiter, self, RT_MUTEX_MIN_CHAINWALK);
- BUG_ON(ret);
+ BUG_ON(task_blocks_on_rt_mutex(lock, &waiter, self, RT_MUTEX_MIN_CHAINWALK));
for (;;) {
/* Try to acquire the lock again. */
@@ -1051,11 +1050,12 @@ static void noinline __sched rt_spin_lo
debug_rt_mutex_print_deadlock(&waiter);
if (top_waiter != &waiter || adaptive_wait(lock, lock_owner)) {
- if (mg_off)
+ if (mg_off && self->migrate_disable == 1) {
+ mg_off = false;
+ mg_disable = true;
migrate_enable();
+ }
schedule();
- if (mg_off)
- migrate_disable();
}
raw_spin_lock_irqsave(&lock->wait_lock, flags);
@@ -1088,6 +1088,9 @@ static void noinline __sched rt_spin_lo
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
+ if (mg_disable)
+ migrate_disable();
+
debug_rt_mutex_free_waiter(&waiter);
}
next prev parent reply other threads:[~2016-03-20 8:43 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-12 23:02 [PATCH RT 1/6] kernel: softirq: unlock with irqs on Sebastian Andrzej Siewior
2016-02-12 23:02 ` [PATCH RT 2/6] kernel: migrate_disable() do fastpath in atomic & irqs-off Sebastian Andrzej Siewior
2016-02-12 23:02 ` [PATCH RT 3/6] rtmutex: push down migrate_disable() into rt_spin_lock() Sebastian Andrzej Siewior
2016-02-12 23:02 ` [PATCH RT 4/6] rt/locking: Reenable migration accross schedule Sebastian Andrzej Siewior
2016-03-20 8:43 ` Mike Galbraith [this message]
2016-03-24 10:07 ` Mike Galbraith
2016-03-24 10:44 ` Thomas Gleixner
2016-03-24 11:06 ` Mike Galbraith
2016-03-25 5:38 ` Mike Galbraith
2016-03-25 8:52 ` Thomas Gleixner
2016-03-25 9:13 ` Mike Galbraith
2016-03-25 9:14 ` Mike Galbraith
2016-03-25 16:24 ` Mike Galbraith
2016-03-29 4:05 ` Mike Galbraith
2016-03-31 6:31 ` Mike Galbraith
2016-04-01 21:11 ` Sebastian Andrzej Siewior
2016-04-02 3:12 ` Mike Galbraith
2016-04-05 12:49 ` [rfc patch 0/2] Kill hotplug_lock()/hotplug_unlock() Mike Galbraith
[not found] ` <1459837988.26938.16.camel@gmail.com>
2016-04-05 12:49 ` [rfc patch 1/2] rt/locking/hotplug: " Mike Galbraith
2016-04-05 12:49 ` [rfc patch 2/2] rt/locking/hotplug: Fix rt_spin_lock_slowlock() migrate_disable() bug Mike Galbraith
2016-04-06 12:00 ` Mike Galbraith
2016-04-07 4:37 ` Mike Galbraith
2016-04-07 16:48 ` Sebastian Andrzej Siewior
2016-04-07 19:08 ` Mike Galbraith
2016-04-07 16:47 ` [PATCH RT 4/6] rt/locking: Reenable migration accross schedule Sebastian Andrzej Siewior
2016-04-07 19:04 ` Mike Galbraith
2016-04-08 10:30 ` Sebastian Andrzej Siewior
2016-04-08 12:10 ` Mike Galbraith
2016-04-08 6:35 ` Mike Galbraith
2016-04-08 13:44 ` Mike Galbraith
2016-04-08 13:58 ` Sebastian Andrzej Siewior
2016-04-08 14:16 ` Mike Galbraith
2016-04-08 14:51 ` Sebastian Andrzej Siewior
2016-04-08 16:49 ` Mike Galbraith
2016-04-18 17:15 ` Sebastian Andrzej Siewior
2016-04-18 17:55 ` Mike Galbraith
2016-04-19 7:07 ` Sebastian Andrzej Siewior
2016-04-19 8:55 ` Mike Galbraith
2016-04-19 9:02 ` Sebastian Andrzej Siewior
2016-02-12 23:02 ` [PATCH RT 5/6] kernel/stop_machine: partly revert "stop_machine: Use raw spinlocks" Sebastian Andrzej Siewior
2016-02-12 23:02 ` [PATCH RT 6/6] rcu: disable more spots of rcu_bh Sebastian Andrzej Siewior
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