From: Peter Zijlstra <peterz@infradead.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
linux-rt-users <linux-rt-users@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
John Kacur <jkacur@redhat.com>,
LKML <linux-kernel@vger.kernel.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Sasha Levin <sasha.levin@oracle.com>
Subject: Re: [PATCH 3.14-rt] sched/numa: Fix task_numa_free() lockdep splat
Date: Tue, 27 May 2014 20:25:41 +0200 [thread overview]
Message-ID: <20140527182541.GH11096@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20140527141836.4f466086@gandalf.local.home>
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On Tue, May 27, 2014 at 02:18:36PM -0400, Steven Rostedt wrote:
> [ moving this to LKML from linux-rt-users, as that's where it should be ]
>
> On Sat, 17 May 2014 05:36:59 +0200
> Mike Galbraith <umgwanakikbuti@gmail.com> wrote:
>
> > 3.14-rt being build with a non-rt config is unlikely, but..
> >
> > >From 60e69eed85bb7b5198ef70643b5895c26ad76ef7 Mon Sep 17 00:00:00 2001
> > From: Mike Galbraith <bitbucket@online.de>
> > Date: Mon, 7 Apr 2014 10:55:15 +0200
> > Subject: [PATCH] sched/numa: Fix task_numa_free() lockdep splat
> >
> > Sasha reported that lockdep claims that the following commit:
> > made numa_group.lock interrupt unsafe:
> >
> > 156654f491dd ("sched/numa: Move task_numa_free() to __put_task_struct()")
> >
> > While I don't see how that could be, given the commit in question moved
> > task_numa_free() from one irq enabled region to another, the below does
> > make both gripes and lockups upon gripe with numa=fake=4 go away.
>
> It wasn't the irqs that was causing the lockdep splat, but the
> softirqs. You moved it into __put_task_struct() which is called as a
> rcu callback that gets called from soft irqs. So yes, you need to
> prevent softirqs from happening whenever you take the lock.
> spin_lock_irq() is a bigger hammer than needed. The patch below should
> be good enough.
>
> I kept the double_lock_irq() as there is no double_lock_bh(). Should we
> bother to make one?
Nope, its really IRQs.
do_exit()
exit_itimers()
itimer_delete()
spin_lock_irqsave(&timer->it_lock, &flags);
timer_delete_hook(timer);
kc->timer_del(timer) := posix_cpu_timer_del()
put_task_struct()
__put_task_struct()
task_numa_free()
spin_lock(&grp->lock);
Which nests the grp->lock inside the timer->it_lock, and where the
timer->it_lock is IRQ-safe, the grp->lock is not.
This allows for IRQ deadlocks.
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next prev parent reply other threads:[~2014-05-27 18:25 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-09 18:12 [ANNOUNCE] 3.14.3-rt5 Sebastian Andrzej Siewior
2014-05-09 22:54 ` Pavel Vasilyev
2014-05-13 15:33 ` Sebastian Andrzej Siewior
2014-05-10 4:15 ` Mike Galbraith
2014-05-13 15:40 ` Sebastian Andrzej Siewior
2014-05-14 3:10 ` Mike Galbraith
2014-05-16 13:53 ` [patch] rt/sched: fix resursion when CONTEXT_TRACKING and PREEMPT_LAZY are enabled Mike Galbraith
2014-05-25 8:16 ` [patch v2] " Mike Galbraith
2014-05-13 13:30 ` [ANNOUNCE] 3.14.3-rt5 Juri Lelli
2015-02-16 11:29 ` Sebastian Andrzej Siewior
2015-02-16 12:34 ` Juri Lelli
[not found] ` <1400297819.9493.11.camel@marge.simpson.net>
2014-05-27 18:18 ` [PATCH 3.14-rt] sched/numa: Fix task_numa_free() lockdep splat Steven Rostedt
2014-05-27 18:25 ` Peter Zijlstra [this message]
2014-05-27 18:52 ` Steven Rostedt
2014-05-27 18:53 ` Steven Rostedt
2014-06-05 14:33 ` [tip:sched/urgent] sched/numa: Fix use of spin_{un}lock_irq() when interrupts are disabled tip-bot for Steven Rostedt
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