linux-kernel - Re: [Bug #28052] [BUG] 2.6.38-rc2: Circular Locking Dependency

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Message-Id: <20110213.102124.258125070.davem@davemloft.net>
Date:	Sun, 13 Feb 2011 10:21:24 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	rjw@...k.pl
Cc:	linux-kernel@...r.kernel.org, kernel-testers@...r.kernel.org,
	maciej.rutecki@...il.com, florian@...kler.org,
	Knut_Petersen@...nline.de
Subject: Re: [Bug #28052] [BUG] 2.6.38-rc2: Circular Locking Dependency

From: "Rafael J. Wysocki" <rjw@...k.pl>
Date: Sun, 13 Feb 2011 00:05:18 +0100 (CET)

> Bug-Entry	: http://bugzilla.kernel.org/show_bug.cgi?id=28052
> Subject		: [BUG] 2.6.38-rc2: Circular Locking Dependency
> Submitter	: Knut Petersen <Knut_Petersen@...nline.de>
> Date		: 2011-01-24 9:25 (20 days old)
> Message-ID	: <4D3D45A3.7040809@...nline.de>
> References	: http://marc.info/?l=linux-kernel&m=129586118515443&w=2

Fixed by:

commit 8d3bdbd55a7e2a3f2c148a4830aa26dd682b21c4
Author: David S. Miller <davem@...emloft.net>
Date:   Tue Feb 8 15:02:50 2011 -0800

    net: Fix lockdep regression caused by initializing netdev queues too early.
    
    In commit aa9421041128abb4d269ee1dc502ff65fb3b7d69 ("net: init ingress
    queue") we moved the allocation and lock initialization of the queues
    into alloc_netdev_mq() since register_netdevice() is way too late.
    
    The problem is that dev->type is not setup until the setup()
    callback is invoked by alloc_netdev_mq(), and the dev->type is
    what determines the lockdep class to use for the locks in the
    queues.
    
    Fix this by doing the queue allocation after the setup() callback
    runs.
    
    This is safe because the setup() callback is not allowed to make any
    state changes that need to be undone on error (memory allocations,
    etc.).  It may, however, make state changes that are undone by
    free_netdev() (such as netif_napi_add(), which is done by the
    ipoib driver's setup routine).
    
    The previous code also leaked a reference to the &init_net namespace
    object on RX/TX queue allocation failures.
    
    Signed-off-by: David S. Miller <davem@...emloft.net>
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