Messages in this thread | | | Subject | Re: 2.6.24-rc6: possible recursive locking detected | From | Peter Zijlstra <> | Date | Sat, 05 Jan 2008 18:01:16 +0100 |
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On Sat, 2008-01-05 at 17:53 +0100, Peter Zijlstra wrote: > On Sat, 2008-01-05 at 18:12 +1100, Herbert Xu wrote: > > On Fri, Jan 04, 2008 at 09:30:49AM +0100, Ingo Molnar wrote: > > > > > > > > [ 1310.670986] ============================================= > > > > > [ 1310.671690] [ INFO: possible recursive locking detected ] > > > > > [ 1310.672097] 2.6.24-rc6 #1 > > > > > [ 1310.672421] --------------------------------------------- > > > > > [ 1310.672828] FahCore_a0.exe/3692 is trying to acquire lock: > > > > > [ 1310.673238] (&q->lock){++..}, at: [<c011544b>] __wake_up+0x1b/0x50 > > > > > [ 1310.673869] > > > > > [ 1310.673870] but task is already holding lock: > > > > > [ 1310.674567] (&q->lock){++..}, at: [<c011544b>] __wake_up+0x1b/0x50 > > > > > [ 1310.675267] > > > > > [ 1310.675268] other info that might help us debug this: > > > > > [ 1310.675952] 5 locks held by FahCore_a0.exe/3692: > > > > > [ 1310.676334] #0: (rcu_read_lock){..--}, at: [<c038b620>] net_rx_action+0x60/0x1b0 > > > > > [ 1310.677251] #1: (rcu_read_lock){..--}, at: [<c0388d60>] netif_receive_skb+0x100/0x470 > > > > > [ 1310.677924] #2: (rcu_read_lock){..--}, at: [<c03a7fb2>] ip_local_deliver_finish+0x32/0x210 > > > > > [ 1310.678460] #3: (clock-AF_INET){-.-?}, at: [<c038164e>] sock_def_readable+0x1e/0x80 > > > > > [ 1310.679250] #4: (&q->lock){++..}, at: [<c011544b>] __wake_up+0x1b/0x50 > > > > The net part might just be a red herring, since the problem is that > > __wake_up is somehow reentering itself. > > /* > * Perform a safe wake up of the poll wait list. The problem is that > * with the new callback'd wake up system, it is possible that the > * poll callback is reentered from inside the call to wake_up() done > * on the poll wait queue head. The rule is that we cannot reenter the > * wake up code from the same task more than EP_MAX_POLLWAKE_NESTS times, > * and we cannot reenter the same wait queue head at all. This will > * enable to have a hierarchy of epoll file descriptor of no more than > * EP_MAX_POLLWAKE_NESTS deep. We need the irq version of the spin lock > * because this one gets called by the poll callback, that in turn is called > * from inside a wake_up(), that might be called from irq context. > */ > > Seems to suggest that the epoll code can indeed recurse into wakeup. > > Davide, Johannes, any ideas?
Since EP_MAX_POLLWAKE_NESTS < MAX_LOCKDEP_SUBCLASSES we could perhaps do something like:
wake_up_nested(..., wake_nests);
although I'm not quite sure that is correct, my understanding of this code is still fragile at best.
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