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From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Ed Tomlinson <edt@aei.ca>,
	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 11:33:19 -0700	[thread overview]
Message-ID: <20110715183319.GG2327@linux.vnet.ibm.com> (raw)
In-Reply-To: <1310751751.27864.74.camel@gandalf.stny.rr.com>

On Fri, Jul 15, 2011 at 01:42:31PM -0400, Steven Rostedt wrote:
> On Fri, 2011-07-15 at 10:24 -0700, Paul E. McKenney wrote:
> 
> > But the rcu_read_unlock() called from within the irq handler would
> > take a second snapshot of ->special.  It could then enter
> > rcu_read_unlock_special().
> 
> You agree that an interrupt preempting the rcu_read_unlock() is causing
> the issues correct? But it is also contained within rcu_read_unlock().
> That is, we just don't want interrupts or softirqs from calling the
> special function when it preempted rcu_read_unlock().
> 
> How about this patch? (again totally untested and not even compiled)

I really dislike the added overhead, especially the implied
preempt_disable() and preempt_enable() calls.  I am actually trying to
-reduce- its overhead, for example, by removing the function call...

But as a short-term hack-around, it could be OK.  It does seem to
cover all the possible conditions, at least all the ones I can see at
the moment.

Longer term, enclosing the rq/pi lock critical sections with
rcu_read_lock() and rcu_read_unlock() seems more reasonable.

Hmmm...  Does just setting CONFIG_IRQ_FORCED_THREADING suffice to test
this stuff?  Or is "threadirqs" also required on the kernel command line?

							Thanx, Paul

> -- Steve
> 
> diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
> index 7784bd2..0bdf0ea 100644
> --- a/kernel/rcupdate.c
> +++ b/kernel/rcupdate.c
> @@ -46,6 +46,8 @@
>  #include <linux/module.h>
>  #include <linux/hardirq.h>
> 
> +DEFINE_PER_CPU(int, in_rcu_read_unlock);
> +
>  #ifdef CONFIG_DEBUG_LOCK_ALLOC
>  static struct lock_class_key rcu_lock_key;
>  struct lockdep_map rcu_lock_map =
> diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
> index 14dc7dd..a4adbb7 100644
> --- a/kernel/rcutree_plugin.h
> +++ b/kernel/rcutree_plugin.h
> @@ -375,6 +375,8 @@ static void rcu_read_unlock_special(struct task_struct *t)
>  	}
>  }
> 
> +DECLARE_PER_CPU(int, in_rcu_read_unlock);
> +
>  /*
>   * Tree-preemptible RCU implementation for rcu_read_unlock().
>   * Decrement ->rcu_read_lock_nesting.  If the result is zero (outermost
> @@ -386,12 +388,16 @@ void __rcu_read_unlock(void)
>  {
>  	struct task_struct *t = current;
> 
> +	get_cpu_var(in_rcu_read_unlock)++;
>  	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 &&
> +	    __get_cpu_var(in_rcu_read_unlock) == 1 &&
>  	    unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
>  		rcu_read_unlock_special(t);
> +	__get_cpu_var(in_rcu_read_unlock)--;
> +	put_cpu_var(in_rcu_read_unlock);
>  #ifdef CONFIG_PROVE_LOCKING
>  	WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0);
>  #endif /* #ifdef CONFIG_PROVE_LOCKING */
> 
> 
> --
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  reply	other threads:[~2011-07-15 18:34 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
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 [this message]
  -- 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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