From 53d374979ef147ab51f5d632dfe20b14aebeccd0 Mon Sep 17 00:00:00 2001 From: Cong Wang Date: Wed, 15 Jan 2020 13:02:38 -0800 Subject: [PATCH] net: avoid updating qdisc_xmit_lock_key in netdev_update_lockdep_key() 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 Signed-off-by: Cong Wang Acked-by: Taehee Yoo Signed-off-by: David S. Miller --- net/core/dev.c | 12 ------------ 1 file changed, 12 deletions(-) diff --git a/net/core/dev.c b/net/core/dev.c index 0ad39c87b7fd..7e885d069707 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -9177,22 +9177,10 @@ static void netdev_unregister_lockdep_key(struct net_device *dev) 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); -- 2.30.2