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

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Message-ID: <20120731151808.GF2422@linux.vnet.ibm.com>
Date:	Tue, 31 Jul 2012 08:18:09 -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 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?

							Thanx, Paul

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