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authorCong Wang <xiyou.wangcong@gmail.com>2020-01-15 13:02:38 -0800
committerDavid S. Miller <davem@davemloft.net>2020-01-17 11:02:44 +0100
commit53d374979ef147ab51f5d632dfe20b14aebeccd0 (patch)
tree8eff9015b047aea4024a5b23a40b13c646b42b3d /net
parent44c23d71599f81a1c7fe8389e0319822dd50c37c (diff)
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 <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>
Diffstat (limited to 'net')
-rw-r--r--net/core/dev.c12
1 files changed, 0 insertions, 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);

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