netpoll: fix a rtnl lock assertion failure

v4: hold rtnl lock for the whole netpoll_setup()
v3: remove the comment
v2: use RCU read lock

This patch fixes the following warning:

[   72.013864] RTNL: assertion failed at net/core/dev.c (4955)
[   72.017758] Pid: 668, comm: netpoll-prep-v6 Not tainted 3.8.0-rc1+ #474
[   72.019582] Call Trace:
[   72.020295]  [<ffffffff8176653d>] netdev_master_upper_dev_get+0x35/0x58
[   72.022545]  [<ffffffff81784edd>] netpoll_setup+0x61/0x340
[   72.024846]  [<ffffffff815d837e>] store_enabled+0x82/0xc3
[   72.027466]  [<ffffffff815d7e51>] netconsole_target_attr_store+0x35/0x37
[   72.029348]  [<ffffffff811c3479>] configfs_write_file+0xe2/0x10c
[   72.030959]  [<ffffffff8115d239>] vfs_write+0xaf/0xf6
[   72.032359]  [<ffffffff81978a05>] ? sysret_check+0x22/0x5d
[   72.033824]  [<ffffffff8115d453>] sys_write+0x5c/0x84
[   72.035328]  [<ffffffff819789d9>] system_call_fastpath+0x16/0x1b

In case of other races, hold rtnl lock for the entire netpoll_setup() function.

Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Cong Wang <amwang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 10 insertions, 14 deletions

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index 9f0506726101..a5ad1c1c4b18 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -1048,11 +1048,13 @@ int netpoll_setup(struct netpoll *np)
         struct in_device *in_dev;
         int err;
 
+        rtnl_lock();
         if (np->dev_name)
-                ndev = dev_get_by_name(&init_net, np->dev_name);
+                ndev = __dev_get_by_name(&init_net, np->dev_name);
         if (!ndev) {
                 np_err(np, "%s doesn't exist, aborting\n", np->dev_name);
-                return -ENODEV;
+                err = -ENODEV;
+                goto unlock;
         }
 
         if (netdev_master_upper_dev_get(ndev)) {
@@ -1066,15 +1068,14 @@ int netpoll_setup(struct netpoll *np)
 
                 np_info(np, "device %s not up yet, forcing it\n", np->dev_name);
 
-                rtnl_lock();
                 err = dev_open(ndev);
-                rtnl_unlock();
 
                 if (err) {
                         np_err(np, "failed to open %s\n", ndev->name);
                         goto put;
                 }
 
+                rtnl_unlock();
                 atleast = jiffies + HZ/10;
                 atmost = jiffies + carrier_timeout * HZ;
                 while (!netif_carrier_ok(ndev)) {
@@ -1094,16 +1095,14 @@ int netpoll_setup(struct netpoll *np)
                         np_notice(np, "carrier detect appears untrustworthy, waiting 4 seconds\n");
                         msleep(4000);
                 }
+                rtnl_lock();
         }
 
         if (!np->local_ip.ip) {
                 if (!np->ipv6) {
-                        rcu_read_lock();
-                        in_dev = __in_dev_get_rcu(ndev);
-
+                        in_dev = __in_dev_get_rtnl(ndev);
 
                         if (!in_dev || !in_dev->ifa_list) {
-                                rcu_read_unlock();
                                 np_err(np, "no IP address for %s, aborting\n",
                                        np->dev_name);
                                 err = -EDESTADDRREQ;
@@ -1111,14 +1110,12 @@ int netpoll_setup(struct netpoll *np)
                         }
 
                         np->local_ip.ip = in_dev->ifa_list->ifa_local;
-                        rcu_read_unlock();
                         np_info(np, "local IP %pI4\n", &np->local_ip.ip);
                 } else {
 #if IS_ENABLED(CONFIG_IPV6)
                         struct inet6_dev *idev;
 
                         err = -EDESTADDRREQ;
-                        rcu_read_lock();
                         idev = __in6_dev_get(ndev);
                         if (idev) {
                                 struct inet6_ifaddr *ifp;
@@ -1133,7 +1130,6 @@ int netpoll_setup(struct netpoll *np)
                                 }
                                 read_unlock_bh(&idev->lock);
                         }
-                        rcu_read_unlock();
                         if (err) {
                                 np_err(np, "no IPv6 address for %s, aborting\n",
                                        np->dev_name);
@@ -1151,17 +1147,17 @@ int netpoll_setup(struct netpoll *np)
         /* fill up the skb queue */
         refill_skbs();
 
-        rtnl_lock();
         err = __netpoll_setup(np, ndev, GFP_KERNEL);
-        rtnl_unlock();
-
         if (err)
                 goto put;
 
+        rtnl_unlock();
         return 0;
 
 put:
         dev_put(ndev);
+unlock:
+        rtnl_unlock();
         return err;
 }
 EXPORT_SYMBOL(netpoll_setup);