Messages in this thread | | | Date | Wed, 11 Oct 2006 12:48:20 +0200 | From | "Michal Piotrowski" <> | Subject | Re: 2.6.19-rc1-mm1 |
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On 11/10/06, Neil Brown <neilb@suse.de> wrote: > On Tuesday October 10, michal.k.k.piotrowski@gmail.com wrote: > > On 10/10/06, Michal Piotrowski <michal.k.k.piotrowski@gmail.com> wrote: > > > Hi, > > > > > > On 10/10/06, Andrew Morton <akpm@osdl.org> wrote: > > > > > > > > ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.19-rc1/2.6.19-rc1-mm1/ > > > > > > > > > > Kernel 2.6.19-rc1-mm1 + Neil's avoid_lockdep_warning_in_md.patch > > > (http://www.ussg.iu.edu/hypermail/linux/kernel/0610.1/0642.html) > > > > > > (I'll try to reproduce this without Neil's patch). > > > > I can't reproduce this without Neil's patch. > > > > Despite this circumstantial evidence, I don't see how my patch could > possible have an effect here.... > > Looking at the code, starting at _cpu_down in the CONFIG_HOTPLUG_CPU > case, the call notifier chain 'cpu_chain' contains > workqueue_cpu_callback which does 'mutex_lock(&workqueue_mutex)' in > the "DOWN_PREPARE" case and mutex_unlock(&workqueue_mutex) in the > DOWN_FAILED and DEAD cases. > > blocking_notifier_call_chain is > down_read(&nh->rwsem); > ret = notifier_call_chain(&nh->head, val, v); > up_read(&nh->rwsem); > > and so holds ->rwsem while calling the callback. > So the locking sequence ends up as: > > down_read(&cpu_chain.rwsem); > mutex_lock(&workqueue_mutex); > up_read(&cpu_chain.rwsem); > > down_read(&cpu_chain.rwsem); > mutex_unlock(&workqueue_mutex); > up_read(&workqueue_mutex); > > and lockdep doesn't seem to like this. It sees workqueue_mutex > claimed while cpu_chain.rwsem is held. and then it sees > cpu_chain.rwsem claimed while workqueue_mutex is held, which looks a > bit like a class ABBA deadlock. > Of course because it is a 'down_read' rather than a 'down', it isn't > really a dead lock. > > I don't know how to tell lockdep to do the right thing, but I'll leave > that up to Ingo et al. > > Why it didn't trigger without my patch I cannot imagine. Are you sure > the config was identical (you didn't remove CONFIG_HOTPLUG_CPU or > anything did you?).
No, I didn't remove CONFIG_HOTPLUG_CPU or anything else.
I didn't do enough testing - only a few hibernatins.
> > NeilBrown >
Regards, Michal
-- Michal K. K. Piotrowski LTG - Linux Testers Group (http://www.stardust.webpages.pl/ltg/) - 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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