linux-kernel - Re: [PATCH 2/2] lockdep: Don't only check recursive read locks once in a sequence

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Date:	Fri, 20 Nov 2009 01:57:46 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ming Lei <tom.leiming@...il.com>
Subject: Re: [PATCH 2/2] lockdep: Don't only check recursive read locks
	once in a sequence

On Thu, Nov 19, 2009 at 06:13:48PM +0100, Peter Zijlstra wrote:
> On Thu, 2009-11-19 at 16:55 +0100, Frederic Weisbecker wrote:
> > And btw I
> > don't understand why rwsem read locks are not considered as
> > recursive in lockdep. 
> 
> Because they're not.
> 
> rwsems are FIFO fair, so a double read can deadlock when there's a
> pending writer inbetween.
> 


Aah ok. That's the subtle thing I was missing :)

Thanks.

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