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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?). NeilBrown > > > > echo shutdown > /sys/power/disk; echo disk > /sys/power/state > > > > ======================================================= > > [ INFO: possible circular locking dependency detected ] > > 2.6.19-rc1-mm1 #4 > > ------------------------------------------------------- - 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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