linux-kernel - Re: [PATCH RFC tip/core/rcu 7/7] rcu: Quiet RCU-lockdep warnings involving interrupt disabling

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Message-ID: <1323078096.32012.14.camel@twins>
Date:	Mon, 05 Dec 2011 10:41:36 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, rostedt@...dmis.org,
	Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com, patches@...aro.org,
	Yong Zhang <yong.zhang0@...il.com>
Subject: Re: [PATCH RFC tip/core/rcu 7/7] rcu: Quiet RCU-lockdep warnings
 involving interrupt disabling

On Sat, 2011-12-03 at 10:34 -0800, Paul E. McKenney wrote:
> From: Yong Zhang <yong.zhang0@...il.com>
> 
> RCU-lockdep will issue warnings given the following use pattern:
> 
> 	rcu_read_lock();
> 	local_irq_disable();
> 	rcu_read_unlock();
> 	local_irq_enable();
> 
> However, this use pattern is legal except for the scheduler's runqueue
> and priority-inheritance locks (and any other locks that the scheduler
> might use during priority-inheritance operations).

So what does this patch do? Make it not complain when you do the above?
How often does this pattern actually happen? Can't be that often
otherwise we'd have had more complaints, no?


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