From: Arjan van de Ven <arjan@infradead.org>
To: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Andrew Morton <akpm@osdl.org>, Greg KH <gregkh@suse.de>,
Dave Jones <davej@codemonkey.org.uk>,
linux-kernel@vger.kernel.org
Subject: Re: Lockdep message on workqueue_mutex
Date: Tue, 22 Aug 2006 14:36:32 +0200 [thread overview]
Message-ID: <1156250192.2976.47.camel@laptopd505.fenrus.org> (raw)
In-Reply-To: <20060822121042.GA29577@osiris.boeblingen.de.ibm.com>
On Tue, 2006-08-22 at 14:10 +0200, Heiko Carstens wrote:
> git commit 9b41ea7289a589993d3daabc61f999b4147872c4 causes the lockdep
> message below on cpu hotplug (git kernel of today).
>
> We have:
>
> cpu_down (takes cpu_add_remove_lock)
> [CPU_DOWN_PREPARE]
> blocking_notifier_call_chain (takes (cpu_chain).rwsem)
> workqueue_cpu_callback (takes workqueue_mutex)
> blocking_notifier_call_chain (releases (cpu_chain).rwsem)
> [CPU_DEAD]
> blocking_notifier_call_chain (takes (cpu_chain).rwsem)
> ^^^^^^^^^^^^^^^^^^^^^^^
> -> reverse locking order, since we still hold workqueue_mutex.
>
> But since all of this is protected by the cpu_add_remove_lock this looks
> legal. Well, at least it's safe as long as no other cpu callback function
> does anything that will take the workqueue_mutex as well.
so you're saying this locking is entirely redundant ? ;-)
next prev parent reply other threads:[~2006-08-22 12:36 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-08-22 12:10 Heiko Carstens
2006-08-22 12:36 ` Arjan van de Ven [this message]
2006-08-22 13:53 ` Heiko Carstens
2006-08-22 14:36 ` Andrew Morton
2006-08-22 14:26 ` Andrew Morton
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