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net: avoid updating qdisc_xmit_lock_key in netdev_update_lockdep_key()

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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: ab92d68fc2 ("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>
This commit is contained in:
Cong Wang 2020-01-15 13:02:38 -08:00 committed by David S. Miller
parent 44c23d7159
commit 53d374979e
1 changed files with 0 additions and 12 deletions
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12
net/core/dev.c
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@ -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);