From: Cong Wang xiyou.wangcong@gmail.com
[ Upstream commit 53d374979ef147ab51f5d632dfe20b14aebeccd0 ]
syzbot reported some bogus lockdep warnings, for example bad unlock balance in sch_direct_xmit(). They are due to a race condition between slow path and fast path, that is qdisc_xmit_lock_key gets re-registered in netdev_update_lockdep_key() on slow path, while we could still acquire the queue->_xmit_lock on fast path in this small window:
CPU A CPU B __netif_tx_lock(); lockdep_unregister_key(qdisc_xmit_lock_key); __netif_tx_unlock(); lockdep_register_key(qdisc_xmit_lock_key);
In fact, unlike the addr_list_lock which has to be reordered when the master/slave device relationship changes, queue->_xmit_lock is only acquired on fast path and only when NETIF_F_LLTX is not set, so there is likely no nested locking for it.
Therefore, we can just get rid of re-registration of qdisc_xmit_lock_key.
Reported-by: syzbot+4ec99438ed7450da6272@syzkaller.appspotmail.com Fixes: ab92d68fc22f ("net: core: add generic lockdep keys") Cc: Taehee Yoo ap420073@gmail.com Signed-off-by: Cong Wang xiyou.wangcong@gmail.com Acked-by: Taehee Yoo ap420073@gmail.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/core/dev.c | 12 ------------ 1 file changed, 12 deletions(-)
--- a/net/core/dev.c +++ b/net/core/dev.c @@ -8953,22 +8953,10 @@ static void netdev_unregister_lockdep_ke
void netdev_update_lockdep_key(struct net_device *dev) { - struct netdev_queue *queue; - int i; - - lockdep_unregister_key(&dev->qdisc_xmit_lock_key); lockdep_unregister_key(&dev->addr_list_lock_key); - - lockdep_register_key(&dev->qdisc_xmit_lock_key); lockdep_register_key(&dev->addr_list_lock_key);
lockdep_set_class(&dev->addr_list_lock, &dev->addr_list_lock_key); - for (i = 0; i < dev->num_tx_queues; i++) { - queue = netdev_get_tx_queue(dev, i); - - lockdep_set_class(&queue->_xmit_lock, - &dev->qdisc_xmit_lock_key); - } } EXPORT_SYMBOL(netdev_update_lockdep_key);