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Date: Fri, 20 Nov 2009 01:57:46 +0100
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>, Ingo Molnar <mingo@elte.hu>,
       LKML <linux-kernel@vger.kernel.org>,
       Thomas Gleixner <tglx@linutronix.de>, Ming Lei <tom.leiming@gmail.com>
Subject: Re: [PATCH 2/2] lockdep: Don't only check recursive read locks
	once in a sequence
Message-ID: <20091120005743.GJ4967@nowhere>
References: <1258506398-5151-1-git-send-email-fweisbec@gmail.com> <1258506398-5151-3-git-send-email-fweisbec@gmail.com> <4B03C1A7.4070305@cn.fujitsu.com> <20091119155549.GB4967@nowhere> <1258650828.3931.437.camel@laptop>
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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.