linux-kernel - Re: [Patch] workqueue: move lockdep annotations up to destroy

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Message-ID: <4BB43CF4.5020403@kernel.org>
Date:	Thu, 01 Apr 2010 15:28:04 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Cong Wang <amwang@...hat.com>
CC:	Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	akpm@...ux-foundation.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: [Patch] workqueue: move lockdep annotations up to	destroy_workqueue()

Hello,

On 04/01/2010 03:05 PM, Cong Wang wrote:
>> Hmm, it looks like I misunderstand lock_map_acquire()? From the
>> changelog, I thought it was added to complain its caller is holding
>> a lock when invoking it, thus cpu_add_remove_lock is not an
>> exception.

Oh, that just tells the code is trying to grab a pseudo lock.  It's
not really a lock but to lockdep it looks like one and lockdep can use
it to compute problem cases.

> Oh, I see, wq->lockdep_map is acquired again in run_workqueue(), so
> I was wrong. :) I think you and Oleg are right, the lockdep warning
> is not irrelevant.

Yeah, I think the circular dependency you reported on wq->lockdep_map
is completed only through dependency through rtnl_mutex.  If you fix
rtnl_mutex locking, it should go away too.

Thanks.

-- 
tejun
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