Messages in this thread | | | Subject | Re: [Bugme-new] [Bug 10326] New: inconsistent lock state in net_rx_action | From | Peter Zijlstra <> | Date | Thu, 27 Mar 2008 11:56:19 +0100 |
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On Thu, 2008-03-27 at 02:18 -0700, Andrew Morton wrote: > On Thu, 27 Mar 2008 09:55:42 +0100 Jarek Poplawski <jarkao2@gmail.com> wrote: > > > On Wed, Mar 26, 2008 at 05:14:03PM -0700, Andrew Morton wrote: > > ... > > > > >> http://bugzilla.kernel.org/show_bug.cgi?id=10326 > > ... > > > No, it's not an irq_disable() thing, directly. > > > > > > What lockdep is saying is that sky2_poll() is taking napi->poll_lock for > > > writing with softirqs enabled, but net_rx_action() takes the same lock from > > > within softirq context. > > > > > > If sky2_poll() always takes napi->poll_lock under local_irq_disable() then > > > that would be a lockdep bug. > > > > sky2_poll() doesn't take napi->poll_lock; this lock is taken by > > netpoll_poll() before calling sky2_poll(). And before this hardirqs > > are disabled in write_msg(). So, theoretically lockdep could be right > > if sky2_poll() would enable irqs after this. (If it were done in > > netpoll - lockdep should warn before or after sky2_poll() call.) > > But I really can't see any such possibility in sky2_poll(). > > I can't spot it from a five-minute read either. gcc's autoinlining really > makes this sort of thing much harder than it used to be :( > > Anyway, the accusation is that lockdep is busted, in that it doesn't realise that > local_irq_disable() blocks softirqs. > > I bet the net code is wrong and we missed it ;)
How about this:
<irqs disabled>
netpoll_poll() poll_napi() spin_trylock(&napi->poll_lock) poll_one_napi() napi->poll() := sky2_poll() napi_complete() local_irq_disable() local_irq_enable() <--- *BUG*
<irq> irq_exit() do_softirq() net_rx_action() spin_lock(&napi->poll_lock) <--- Deadlock!
Because we still hold the lock....
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