linux-kernel - Re: __update_max_tr: rcu_read_lock() used illegally while idle!

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Message-ID: <1343749502.27983.57.camel@gandalf.stny.rr.com>
Date:	Tue, 31 Jul 2012 11:45:02 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Fengguang Wu <fengguang.wu@...el.com>,
	Steven Rostedt <srostedt@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	David Howells <dhowells@...hat.com>
Subject: Re: __update_max_tr: rcu_read_lock() used illegally while idle!

On Tue, 2012-07-31 at 08:18 -0700, Paul E. McKenney wrote:
> On Tue, Jul 31, 2012 at 10:56:23AM -0400, Steven Rostedt wrote:
> > On Tue, 2012-07-31 at 10:51 -0400, Steven Rostedt wrote:
> > 
> > > > OK, I will bite.  How about using something like RCU_NONIDLE(), either
> > > > directly or open-coded, to make it a legal call site?
> > > 
> > > OK, then something like:
> > > 
> > > 	RCU_NONIDLE(max_data = task_uid(tsk));
> > > 
> > > would work when called normally or with idle?
> > > 
> > 
> > The comment above RCU_NONIDLE() says:
> > 
> > 	This macro may be used from process-level code only.
> > 
> > Although I'm not sure what a 'level' is. Do you mean process-context? If
> > so, then this will not work because it can be called from non process
> > level code (return from interrupt), or any interrupt that enables
> > interrupts.
> 
> Yep, process context.  It seems that I was naively expecting the
> calls in interrupt context to be covered by rcu_irq_enter() and
> rcu_irq_exit().  I take it that these calls are happening outside of
> the rcu_irq_enter()-protected region?

Yep, it is called by the same hooks that lockdep uses. TRACE_IRQS_ON
inside the irq handler in assembly.

-- Steve


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