From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: LKML <linux-kernel@vger.kernel.org>
Subject: Re: [BUG] stack tracing causes: kernel/module.c:271 module_assert_mutex_or_preempt
Date: Wed, 5 Apr 2017 12:08:10 -0700 [thread overview]
Message-ID: <20170405190810.GJ1600@linux.vnet.ibm.com> (raw)
In-Reply-To: <20170405145425.357937b8@gandalf.local.home>
On Wed, Apr 05, 2017 at 02:54:25PM -0400, Steven Rostedt wrote:
> On Wed, 5 Apr 2017 10:59:25 -0700
> "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:
>
> > > Note, this has nothing to do with trace_rcu_dyntick(). It's the
> > > function tracer tracing inside RCU, calling the stack tracer to record
> > > a new stack if it sees its larger than any stack before. All I need is
> > > a way to tell the stack tracer to not record a stack if it is in this
> > > RCU critical section.
> > >
> > > If you can add a "in_rcu_critical_section()" function, that the stack
> > > tracer can test, and simply exit out like it does if in_nmi() is set,
> > > that would work too. Below is my current work around.
> >
> > Except that the rcu_irq_enter() would already have triggered the bug
> > that was (allegedly) fixed by my earlier patch. So, yes, the check for
> > rcu_is_watching() would work around this bug, but the hope is that
> > with my earlier fix, this workaround would not be needed.
>
> Note, if I had a "in_rcu_critical_section()" I wouldn't need to call
> rcu_irq_enter(). I could fall out before that. My current workaround
> does the check, even though it breaks things, it would hopefully fix
> things as it calls rcu_irq_exit() immediately.
OK, color me confused. What would "in_rcu_critical_section()" do?
The rcu_is_watching() function tells you that RCU is not in an extended
quiescent state, though its return value can be iffy in the middle of
rcu_eqs_enter_common() -- which is why interrupts are disabled there.
In preemptible RCU, you can (but shouldn't) use rcu_preempt_depth()
to determine whether you are within an RCU read-side critical section,
which is what in_rcu_critical_section() sounds like to me, but I don't
see how this information would help in this situation.
What am I missing here?
> Would I would have is:
>
> if (in_rcu_critical_section())
> goto out;
>
> rcu_irq_enter();
>
> which would probably be the easiest fix.
>
>
> >
> > So could you please test my earlier patch?
>
> I could, but it wouldn't tell me anything immediately. It's a hard race
> to hit. Which I never could hit it when I tried, but it would appear to
> hit immediately when testing other things :-p
>
> Remember, it only triggers when a new max stack size is hit. The bug
> happens when that new max stack size is in the rcu critical section.
>
> I guess I could force it to trigger by inserting a call in your code
> that clears the max stack size.
I know it is a bit of a hassle, but I would really appreciate the
testing.
Thanx, Paul
> -- Steve
>
> >
> > This patch does not conflict with anything on -rcu, so you could
> > carry it if that helps.
> >
>
next prev parent reply other threads:[~2017-04-05 19:08 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-05 13:32 [BUG] stack tracing causes: kernel/module.c:271 module_assert_mutex_or_preempt Steven Rostedt
2017-04-05 16:25 ` Paul E. McKenney
2017-04-05 16:45 ` Steven Rostedt
2017-04-05 17:59 ` Paul E. McKenney
2017-04-05 18:54 ` Steven Rostedt
2017-04-05 19:08 ` Paul E. McKenney [this message]
2017-04-05 19:21 ` Steven Rostedt
2017-04-05 19:39 ` Paul E. McKenney
2017-04-05 19:52 ` Steven Rostedt
2017-04-05 20:42 ` Paul E. McKenney
2017-04-06 1:31 ` Steven Rostedt
2017-04-06 4:07 ` Paul E. McKenney
2017-04-06 2:12 ` Steven Rostedt
2017-04-06 4:15 ` Paul E. McKenney
2017-04-06 14:14 ` Steven Rostedt
2017-04-06 14:59 ` Paul E. McKenney
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