Messages in this thread | | | Subject | Re: 2.6.19-rc1-mm1 | From | Arjan van de Ven <> | Date | Wed, 11 Oct 2006 13:23:06 +0200 |
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> > 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.
ok can you explain to me why "down_read" doesn't make this a deadlock while "down" would make it a deadlock? I have trouble following your reasoning.....
(remember that rwsems are strictly fair)
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