net: Write lock dev_base_lock without disabling bottom halves.

The writer acquires dev_base_lock with disabled bottom halves.
The reader can acquire dev_base_lock without disabling bottom halves
because there is no writer in softirq context.

On PREEMPT_RT the softirqs are preemptible and local_bh_disable() acts
as a lock to ensure that resources, that are protected by disabling
bottom halves, remain protected.
This leads to a circular locking dependency if the lock acquired with
disabled bottom halves (as in write_lock_bh()) and somewhere else with
enabled bottom halves (as by read_lock() in netstat_show()) followed by
disabling bottom halves (cxgb_get_stats() -> t4_wr_mbox_meat_timeout()
-> spin_lock_bh()). This is the reverse locking order.

All read_lock() invocation are from sysfs callback which are not invoked
from softirq context. Therefore there is no need to disable bottom
halves while acquiring a write lock.

Acquire the write lock of dev_base_lock without disabling bottom halves.

Reported-by: Pei Zhang <pezhang@redhat.com>
Reported-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 8 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 823917de0d2b..d30adecc2bb2 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -365,12 +365,12 @@ static void list_netdevice(struct net_device *dev)
 
 	ASSERT_RTNL();
 
-	write_lock_bh(&dev_base_lock);
+	write_lock(&dev_base_lock);
 	list_add_tail_rcu(&dev->dev_list, &net->dev_base_head);
 	netdev_name_node_add(net, dev->name_node);
 	hlist_add_head_rcu(&dev->index_hlist,
 			   dev_index_hash(net, dev->ifindex));
-	write_unlock_bh(&dev_base_lock);
+	write_unlock(&dev_base_lock);
 
 	dev_base_seq_inc(net);
 }
@@ -383,11 +383,11 @@ static void unlist_netdevice(struct net_device *dev)
 	ASSERT_RTNL();
 
 	/* Unlink dev from the device chain */
-	write_lock_bh(&dev_base_lock);
+	write_lock(&dev_base_lock);
 	list_del_rcu(&dev->dev_list);
 	netdev_name_node_del(dev->name_node);
 	hlist_del_rcu(&dev->index_hlist);
-	write_unlock_bh(&dev_base_lock);
+	write_unlock(&dev_base_lock);
 
 	dev_base_seq_inc(dev_net(dev));
 }
@@ -1188,15 +1188,15 @@ rollback:
 
 	netdev_adjacent_rename_links(dev, oldname);
 
-	write_lock_bh(&dev_base_lock);
+	write_lock(&dev_base_lock);
 	netdev_name_node_del(dev->name_node);
-	write_unlock_bh(&dev_base_lock);
+	write_unlock(&dev_base_lock);
 
 	synchronize_rcu();
 
-	write_lock_bh(&dev_base_lock);
+	write_lock(&dev_base_lock);
 	netdev_name_node_add(net, dev->name_node);
-	write_unlock_bh(&dev_base_lock);
+	write_unlock(&dev_base_lock);
 
 	ret = call_netdevice_notifiers(NETDEV_CHANGENAME, dev);
 	ret = notifier_to_errno(ret);