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From: Steven Rostedt <>
To: Peter Zijlstra <>
Cc: Fengguang Wu <>,
	Thomas Gleixner <>,
	john stultz <>, Ingo Molnar <>,
	LKML <>,
	"Paul E. McKenney" <>
Subject: Re: lockdep WARNING for run_timer_softirq()
Date: Wed, 05 Sep 2012 15:23:48 -0400	[thread overview]
Message-ID: <1346873028.27919.70.camel@gandalf.local.home> (raw)
In-Reply-To: <1346865555.2600.38.camel@twins>

On Wed, 2012-09-05 at 19:19 +0200, Peter Zijlstra wrote:
> On Wed, 2012-09-05 at 13:14 -0400, Steven Rostedt wrote:
> > 
> > This looks very familiar to Fengguang's previous bug report. I can't
> > seem to find it on Probably because of the two attachments
> > (dmesg and config) caused lkml to nuke it.
> > 
> > I'll forward it to you. 
> Yuck that looks like fun too.. doesn't look like the if() thing though.

I'm able to trigger a similar bug too. And this is what I've found.



the __local_bh_enable() is being traced, which means we call the
ftrace_ops_list_func() (which is called instead of the direct function
in some configs). This does a:

	op = rcu_dereference_raw(ftrace_ops_list);

where rcu_dereference_raw() eventually calls rcu_read_lock_held() which
calls lock_is_held(), and this does the consistency checks, where
lockdep thinks we are no longer in the softirq, but we haven't gotten to
the point in __local_bh_enable() where the preempt_count is decremented
to state this.

But this doesn't look the same as the branch tracer. I'll continue
looking into that one.

-- Steve

      reply	other threads:[~2012-09-05 19:23 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-08-31  7:21 lockdep WARNING for run_timer_softirq() Fengguang Wu
2012-08-31  7:32 ` Fengguang Wu
2012-09-05 11:47 ` Peter Zijlstra
2012-09-05 14:20   ` Steven Rostedt
2012-09-05 17:09     ` Peter Zijlstra
2012-09-05 17:14       ` Steven Rostedt
2012-09-05 17:19         ` Peter Zijlstra
2012-09-05 19:23           ` Steven Rostedt [this message]

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