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From: Steven Rostedt <rostedt@goodmis.org>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Dipankar Sarma <dipankar@in.ibm.com>,
	linux-kernel@vger.kernel.org
Subject: Re: INFO: possible circular locking dependency detected
Date: Thu, 14 Jul 2011 12:58:27 -0400	[thread overview]
Message-ID: <1310662707.27864.38.camel@gandalf.stny.rr.com> (raw)
In-Reply-To: <20110714144946.GA3354@swordfish.minsk.epam.com>

On Thu, 2011-07-14 at 17:49 +0300, Sergey Senozhatsky wrote:
> [ 4172.371363] Chain exists of:
> [ 4172.371363]   rcu_node_level_0 --> sync_rcu_preempt_exp_wq.lock --> &p->pi_lock
> [ 4172.371370] 
> [ 4172.371371]  Possible unsafe locking scenario:
> [ 4172.371372] 
> [ 4172.371374]        CPU0                    CPU1
> [ 4172.371375]        ----                    ----
> [ 4172.371377]   lock(&p->pi_lock);
> [ 4172.371380]                                lock(sync_rcu_preempt_exp_wq.lock);
> [ 4172.371384]                                lock(&p->pi_lock);
> [ 4172.371387]   lock(rcu_node_level_0);
> [ 4172.371390] 
> [ 4172.371390]  *** DEADLOCK *** 

Here's what I found:

Note: rcu_node_level_0 == rnp->lock from rcu_init_one()

	static char *buf[] = { "rcu_node_level_0",
			       "rcu_node_level_1",
			       "rcu_node_level_2",
			       "rcu_node_level_3" };  /* Match MAX_RCU_LVLS */

	[..]
			raw_spin_lock_init(&rnp->lock);
			lockdep_set_class_and_name(&rnp->lock,
						   &rcu_node_class[i], buf[i]);


We have this call chain:

rcu_report_exp_rnp() {
	raw_spin_lock_irqsave(&rnp->lock, flags);
		wake_up(&sync_rcu_preempt_exp_wq);

		__wake_up() {
			/* q == sync_rcu_preempt_exp_wq */
			spin_lock_irqsave(&q->lock, flags);
				try_to_wake_up() {
					raw_spin_lock_irqsave(&p->pi_lock, flags);

Which gives us the noted lock chain:


rcu_node_level_0 --> sync_rcu_preempt_exp_wq.lock --> &p->pi_lock


But then we have:

try_to_wake_up() {
	raw_spin_lock_irqsave(&p->pi_lock, flags);
	select_task_rq_fair() {
		rcu_read_unlock() {
			rcu_read_unlock_special() {
				raw_spin_lock(&rnp->lock);


Now we have the call chain of &p->pi_lock -> rcu_node_level_O

But to call this we have:

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);

Thus the question is, how did we get rcu_read_unlock_special set here?

-- Steve



  parent reply	other threads:[~2011-07-14 16:58 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 [this message]
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
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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