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

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Date:	Thu, 19 Nov 2009 18:13:48 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
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, 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.

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