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

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Message-ID: <20120731182114.GN2422@linux.vnet.ibm.com>
Date:	Tue, 31 Jul 2012 11:21:14 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Steven Rostedt <rostedt@...dmis.org>
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, Jul 31, 2012 at 02:06:41PM -0400, Steven Rostedt wrote:
> On Tue, 2012-07-31 at 10:44 -0700, Paul E. McKenney wrote:
> 
> > OK, I interpret this as excluding NMI handlers, but please let me
> > know if I am still being naive.  ;-)
> > 
> 
> You are correct. This is only called where lockdep is called (to trace
> enabling of IRQS). Note, that its called before normal irqs are actually
> enabled (interrupts are still disabled), this is why it's called outside
> of the in_irq() sections, because it is called just before returning
> back to process context.
> 
> That said, because NMIs are so difficult, lockdep doesn't record the
> disabling (and then enabling) of interrupts when an NMI triggers. Thus,
> the irqsoff tracer also does not record NMIs. Which is fine, because
> NMIs should not take long to run (we can add other mechanisms to time
> NMI length if that is needed), and NMIs should not be enabling
> interrupts nor taking any locks.
> 
> >From arch/x86/kernel/entry_64.S:
> 
> 	/* paranoidentry do_nmi, 0; without TRACE_IRQS_OFF */

Then the patch on my earlier email should do it for you.

							Thanx, Paul

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