linux-kernel - Re: lockdep WARNING on check_critical

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Date:	Thu, 06 Sep 2012 17:56:39 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Fengguang Wu <fengguang.wu@...el.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: lockdep WARNING on check_critical_timing()

On Thu, 2012-09-06 at 14:29 -0700, Paul E. McKenney wrote:
>  
> > Didn't we talk about having the rcu_dereference_raw() not do the check?
> > The function tracer is just too invasive to add work arounds to prevent
> > lockdep from screaming about it.
> 
> Actually, rcu_dereference_raw() is already supposed to bypass the
> lockdep checks.  And the code looks to me like it does the bypass,
> OR-ing "1" into the asssertion condition.
> 
> So what am I missing here?

>From my tree, I see:

#define rcu_dereference_raw(p) rcu_dereference_check(p, 1)

#define rcu_dereference_check(p, c) \
	__rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)

Note the 'c' comes after rcu_read_lock_held()

static inline int rcu_read_lock_held(void)
{
	if (!debug_lockdep_rcu_enabled())
		return 1;
	if (rcu_is_cpu_idle())
		return 0;
	if (!rcu_lockdep_current_cpu_online())
		return 0;
	return lock_is_held(&rcu_lock_map);
}

Then when lock_is_held() is called, we get the false warning message.

-- Steve


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