linux-kernel - Re: 3.11-rc6 genetlink locking fix offends lockdep

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Date:	Tue, 20 Aug 2013 21:10:13 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Ding Tianhong <dingtianhong@...wei.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	"David S. Miller" <davem@...emloft.net>,
	"Otcheretianski, Andrei" <andrei.otcheretianski@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>,
	Pravin B Shelar <pshelar@...ira.com>,
	Thomas Graf <tgraf@...g.ch>
Subject: Re: 3.11-rc6 genetlink locking fix offends lockdep

On Tue, 2013-08-20 at 21:02 +0200, Johannes Berg wrote:
> On Tue, 2013-08-20 at 10:28 +0200, Johannes Berg wrote:
> 
> > The only way to fix this that I see right now (that doesn't rewrite the
> > locking completely) would be to make genetlink use parallel_ops itself,
> > thereby removing the genl_lock() in genl_rcv_msg() and breaking all
> > those lock chains that lockdep reported. After that, it should be safe
> > to use genl_lock() inside all the operations. Something like the patch
> > below, perhaps? Completely untested so far.
> 
> Tested now, and it still causes lockdep to complain, though that's a
> lockdep issue I believe, it thinks that genl_mutex and nlk->cb_mutex can
> be inverted although nlk->cb_mutex exists per family, so we need to
> annotate lockdep there.

No, lockdep is correct - generic netlink uses the same cb_mutex for all
families, obviously, since it's all the same netlink family.

I'll just convert it to RCU.

johannes

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