linux-kernel - Re: 2.6.17-rc6-mm1/pktcdvd - BUG: possible circular locking

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Message-Id: <1152916153.3159.51.camel@laptopd505.fenrus.org>
Date:	Sat, 15 Jul 2006 00:29:13 +0200
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Peter Osterlund <petero2@...ia.com>
Cc:	Laurent Riffard <laurent.riffard@...e.fr>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	axboe@...e.de
Subject: Re: 2.6.17-rc6-mm1/pktcdvd - BUG: possible circular locking


> 
> In the first call chain, do_open -> pkt_open, the bd_mutex object that
> is being locked corresponds to a pktcdvd block device, because those
> are the only devices that have their open method set to pkt_open.
> 
> In the second call chain, pkt_ctl_ioctl -> pkt_new_dev -> do_open, the
> bd_mutex object that is being locked *does not* correspond to a
> pktcdvd block device, because pkt_new_dev will bail out with a "Can't
> chain pktcdvd devices" error if you call it with "dev" set to a
> pktcdvd device.
> 
> Therefore, there is no AB-BA deadlock possibility. The locking
> dependencies are A -> B and B -> A', where it is known that A, B and
> A' are all different.
> 
> So the claim from the lockdep code, "BUG: possible circular locking
> deadlock detected!", is a false alarm.

ok I'll try to find a annotation for that that works
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