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From: Ed Tomlinson <edt@aei.ca>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: paulmck@linux.vnet.ibm.com, Steven Rostedt <rostedt@goodmis.org>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Dipankar Sarma <dipankar@in.ibm.com>,
	linux-kernel@vger.kernel.org
Subject: Re: INFO: possible circular locking dependency detected
Date: Fri, 15 Jul 2011 07:35:49 -0400	[thread overview]
Message-ID: <201107150735.50478.edt@aei.ca> (raw)
In-Reply-To: <1310729362.2586.325.camel@twins>

On Friday 15 July 2011 07:29:22 Peter Zijlstra wrote:
> On Fri, 2011-07-15 at 07:05 -0400, Ed Tomlinson wrote:
> > Jul 14 23:21:18 grover kernel: [  920.659426] -> #1 (rcu_node_level_0){..-...}:
> > Jul 14 23:21:18 grover kernel: [  920.659426]        [<ffffffff8108b7e5>] lock_acquire+0x95/0x140
> > Jul 14 23:21:18 grover kernel: [  920.659426]        [<ffffffff8157808b>] _raw_spin_lock+0x3b/0x50
> > Jul 14 23:21:18 grover kernel: [  920.659426]        [<ffffffff810ba797>] __rcu_read_unlock+0x197/0x2d0
> > Jul 14 23:21:18 grover kernel: [  920.659426]        [<ffffffff8103f2f5>] select_task_rq_fair+0x585/0xa80
> > Jul 14 23:21:18 grover kernel: [  920.659426]        [<ffffffff8104633b>] try_to_wake_up+0x17b/0x360
> > Jul 14 23:21:18 grover kernel: [  920.659426]        [<ffffffff81046575>] wake_up_process+0x15/0x20
> > Jul 14 23:21:18 grover kernel: [  920.659426]        [<ffffffff810528f4>] irq_exit+0xb4/0x100
> > Jul 14 23:21:18 grover kernel: [  920.659426]        [<ffffffff8158197e>] smp_apic_timer_interrupt+0x6e/0x99
> > Jul 14 23:21:18 grover kernel: [  920.659426]        [<ffffffff81580c53>] apic_timer_interrupt+0x13/0x20
> > Jul 14 23:21:18 grover kernel: [  920.659426]        [<ffffffff810ba6e9>] __rcu_read_unlock+0xe9/0x2d0 
> > Jul 14 23:21:18 grover kernel: [  920.659426]        [<ffffffff814c20d4>] sock_def_readable+0x94/0xc0
> 
> Ed, are you perchance running with force_irqthreads?

Yes.  

I'm off to work - will test any patches when I get back in 8-10 hours.

Thanks
Ed

> Paul, what appears to be happening here is that some rcu_read_unlock()
> gets interrupted, possibly before calling rcu_read_unlock_special(),
> possibly not if the interrupt is itself the timer interrupt.
> 
> Supposing ->rcu_read_unlock_special is set before, any wakeup happening
> from an interrupt hitting __rcu_read_unlock():
> 
> void __rcu_read_unlock(void)
> {
>         struct task_struct *t = current;
>                 
>         barrier();  /* needed if we ever invoke rcu_read_unlock in rcutree.c */
>         --t->rcu_read_lock_nesting;
>         barrier();  /* decrement before load of ->rcu_read_unlock_special */
>         if (t->rcu_read_lock_nesting == 0 &&
>             unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
>                 rcu_read_unlock_special(t);
> #ifdef CONFIG_PROVE_LOCKING
>         WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0);
> #endif /* #ifdef CONFIG_PROVE_LOCKING */
> }
> 
> After --t->rcu_read_lock_nesting, but before calling
> rcu_read_unlock_special(), will trigger this lock inversion.
> 
> The alternative case, ->rcu_read_unlock_special is not set yet, it can
> be set if the interrupt hitting in that same spot above, is the timer
> interrupt, and the wakeup happens either from the softirq ran from the
> hard IRQ tail, or as I suspect here happens, the wakeup of ksoftirqd/#.

  reply	other threads:[~2011-07-15 11:35 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-07-14 14:49 Sergey Senozhatsky
2011-07-14 16:41 ` Peter Zijlstra
2011-07-14 16:57   ` Paul E. McKenney
2011-07-14 19:16     ` Sergey Senozhatsky
2011-07-14 19:15   ` Sergey Senozhatsky
2011-07-14 19:34     ` Paul E. McKenney
2011-07-14 19:38       ` Dave Jones
2011-07-14 20:33         ` Paul E. McKenney
2011-07-14 19:38       ` Sergey Senozhatsky
2011-07-14 16:58 ` Steven Rostedt
2011-07-14 17:02   ` Steven Rostedt
2011-07-14 17:05     ` Paul E. McKenney
2011-07-14 17:32       ` Steven Rostedt
2011-07-14 17:46         ` Steven Rostedt
2011-07-14 19:18           ` Paul E. McKenney
2011-07-14 19:41             ` Steven Rostedt
2011-07-14 20:33               ` Paul E. McKenney
2011-07-15 11:05             ` Ed Tomlinson
2011-07-15 11:29               ` Peter Zijlstra
2011-07-15 11:35                 ` Ed Tomlinson [this message]
2011-07-15 11:39                 ` Peter Zijlstra
2011-07-15 18:11                   ` Paul E. McKenney
2011-07-15 12:42                 ` Paul E. McKenney
2011-07-15 13:07                   ` Peter Zijlstra
2011-07-15 14:36                     ` Paul E. McKenney
2011-07-15 15:04                       ` Peter Zijlstra
2011-07-15 15:59                         ` Paul E. McKenney
2011-07-15 16:11                           ` Peter Zijlstra
2011-07-15 16:56                             ` Paul E. McKenney
2011-07-15 21:48                               ` Ed Tomlinson
2011-07-15 22:04                                 ` Paul E. McKenney
2011-07-16 19:42                                   ` Ed Tomlinson
2011-07-17  0:02                                     ` Paul E. McKenney
2011-07-17  1:56                                       ` Ed Tomlinson
2011-07-17 14:28                                         ` Paul E. McKenney
2011-07-18 15:15                                           ` Paul E. McKenney
2011-07-18  9:29                                     ` Peter Zijlstra
2011-07-18 15:29                                       ` Paul E. McKenney
2011-07-15 16:55                     ` Steven Rostedt
2011-07-15 17:03                       ` Paul E. McKenney
2011-07-15 17:16                         ` Steven Rostedt
2011-07-15 17:24                           ` Paul E. McKenney
2011-07-15 17:42                             ` Steven Rostedt
2011-07-15 18:33                               ` Paul E. McKenney
  -- strict thread matches above, loose matches on Subject: below --
2011-08-07 16:22 Justin P. Mattock
2011-08-11 20:57 ` Justin P. Mattock
2009-12-06 10:11 Richard Zidlicky
2009-10-10 23:09 John Kacur
2007-02-08 15:03 Pedro M. López
2006-10-16 14:05 alpha @ steudten Engineering
2006-10-16 14:32 ` Nick Piggin
2006-10-16 15:42   ` Randy Dunlap
2006-10-16 15:46     ` Nick Piggin
2006-10-19  6:02   ` Andrew Morton
2006-10-19  6:30     ` Nick Piggin

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