Messages in this thread | | | Date | Tue, 22 Aug 2006 07:36:40 -0700 | From | Andrew Morton <> | Subject | Re: Lockdep message on workqueue_mutex |
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On Tue, 22 Aug 2006 15:53:27 +0200 Heiko Carstens <heiko.carstens@de.ibm.com> wrote:
> On Tue, Aug 22, 2006 at 02:36:32PM +0200, Arjan van de Ven wrote: > > 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 ? ;-) > > No, I'm just saying that I think that it currently cannot deadlock. But I > think the workqueue cpu hotplug code should be changed, so that it doesn't > return with the workqueue_mutex being held.
That's deliberate: it's to prevent the workqueue code from walking cpu_online_map while it is in the process of being changed. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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