netdev - Re: 2.6.25-rc8-mm1 -- INFO: possible circular locking dependency detected (while using iw to debug a wireless issue)

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Date:	Fri, 4 Apr 2008 21:53:23 +0200
From:	Thomas Graf <tgraf@...g.ch>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Berg <johannes@...solutions.net>,
	Miles Lane <miles.lane@...il.com>, netdev@...r.kernel.org,
	ALSA development <alsa-devel@...a-project.org>,
	YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>
Subject: Re: 2.6.25-rc8-mm1 -- INFO: possible circular locking dependency detected (while using iw to debug a wireless issue)

* Stephen Hemminger <shemminger@...tta.com> 2008-04-04 12:11
> The changes in git-net don't look locking related.  I suspect either:
> wireless is calling netlink without holding rtnl_lock;
> or more likely conditional locking ctrl_dumpfamily is confusing lockdep.
> 
> ctrl_dumpfamily only acquires genl_lock if one of the incoming parameters (chains_to_skip)
> is non-zero. Not sure what the design reason is, Thomas could you add a comment?

First call to ctrl_dumpfamily() is coming directly from the message
processing context where genl_lock is already held. Subsequence calls
come from netlink_recvmsg() so we have to take the lock separately.

However, I just noticed the condition should really be
	chains_to_skip != 0 || fams_to_skip != 0
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