[PATCH RESEND net-next 1/2] net: Remove net_rwsem from {, un}register_netdevice_notifier()

[Kirill Tkhai]

These functions take net_rwsem, while wireless_nlevent_flush()
also takes it. But down_read() can't be taken recursive,
because of rw_semaphore design, which prevents it to be occupied
by only readers forever.

Since we take pernet_ops_rwsem in {,un}register_netdevice_notifier(),
net list can't change, so these down_read()/up_read() can be removed.

Fixes: f0b07bb151b0 "net: Introduce net_rwsem to protect net_namespace_list"
Signed-off-by: Kirill Tkhai <ktk...@virtuozzo.com>
---
 net/core/dev.c |    5 -----
 1 file changed, 5 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 07da7add4845..8edb58829124 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1633,7 +1633,6 @@ int register_netdevice_notifier(struct notifier_block *nb)
                goto unlock;
        if (dev_boot_phase)
                goto unlock;
-       down_read(&net_rwsem);
        for_each_net(net) {
                for_each_netdev(net, dev) {
                        err = call_netdevice_notifier(nb, NETDEV_REGISTER, dev);
@@ -1647,7 +1646,6 @@ int register_netdevice_notifier(struct notifier_block *nb)
                        call_netdevice_notifier(nb, NETDEV_UP, dev);
                }
        }
-       up_read(&net_rwsem);
 
 unlock:
        rtnl_unlock();
@@ -1671,7 +1669,6 @@ int register_netdevice_notifier(struct notifier_block *nb)
        }
 
 outroll:
-       up_read(&net_rwsem);
        raw_notifier_chain_unregister(&netdev_chain, nb);
        goto unlock;
 }
@@ -1704,7 +1701,6 @@ int unregister_netdevice_notifier(struct notifier_block 
*nb)
        if (err)
                goto unlock;
 
-       down_read(&net_rwsem);
        for_each_net(net) {
                for_each_netdev(net, dev) {
                        if (dev->flags & IFF_UP) {
@@ -1715,7 +1711,6 @@ int unregister_netdevice_notifier(struct notifier_block 
*nb)
                        call_netdevice_notifier(nb, NETDEV_UNREGISTER, dev);
                }
        }
-       up_read(&net_rwsem);
 unlock:
        rtnl_unlock();
        up_write(&pernet_ops_rwsem);