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

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Message-ID: <20100331112559.GA17747@redhat.com>
Date:	Wed, 31 Mar 2010 13:25:59 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Amerigo Wang <amwang@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.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()

On 03/31, Amerigo Wang wrote:
>
> This fixes a lockdep warning when invoking destroy_workqueue(),
> because the lockdep annotations are invoked under cpu_add_remove_lock.

Confused. Why does lockdep complains?

> So, move the lockdep annotations before taking cpu_add_remove_lock
> in destroy_workqueue(), this will not affect the original purpose
> of adding them for destroy_workqueue() etc.
>
> However, it will affect another caller of cleanup_workqueue_thread(),
> that is, workqueue_cpu_callback(). This should be fine, because there
> are no other cases than cpu hotplug could call it.

OK, but nobody should take cpu_maps_update_begin() under wq->lockdep_map,
in particular work->func() must not.

I must have missed something, but it seems to me this patch tries to
supress the valid warning.

Could you please clarify?

Oleg.

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