linux-kernel - Re: Incorrect circular locking dependency?

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Message-ID: <18723.1249401004@redhat.com>
Date:	Tue, 04 Aug 2009 16:50:04 +0100
From:	David Howells <dhowells@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	dhowells@...hat.com, Takashi Iwai <tiwai@...e.de>,
	Ingo Molnar <mingo@...e.hu>,
	Linux filesystem caching discussion list 
	<linux-cachefs@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	Johannes Berg <johannes@...solutions.net>,
	oleg <oleg@...hat.com>
Subject: Re: Incorrect circular locking dependency?

Peter Zijlstra <peterz@...radead.org> wrote:

> Creating a new class for your second workqueue might help,

I only have one workqueue.  The problem is there are two waitqueues, but
init_waitqueue_head() always sets q->lock to the same class.

> we'd have to pass a second key through __create_workqueue_key() and pass
> that into init_cpu_workqueue() and apply it to cwq->lock using
> lockdep_set_class() and co.

Actually, wouldn't just making init_cpu_workqueue() apply a class to
cwq->more_work that's common to all workqueues suffice?  Or even, have
init_waitqueue_head() apply an alternate class to q->lock?

David
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