netconsole: fix a deadlock with rtnl and netconsole's mutex

This bug was introduced by commit
7a163bfb7ce50895bbe67300ea610d31b9c09230 ("netconsole: avoid a crash with
multiple sysfs writers"). In store_enabled() we have the following
sequence: acquire nt->mutex then rtnl, but in the netconsole netdev
notifier we have rtnl then nt->mutex effectively leading to a deadlock.
The NULL pointer dereference that the above commit tries to fix is
actually due to another bug in netpoll_cleanup(). This is fixed by dropping
the mutex from the netdev notifier as it's already protected by rtnl.

Signed-off-by: Nikolay Aleksandrov <nikolay@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index dcb21347c67044da535903f2f88ba36f2529f347..adeee615dd19f4e0d7c6288466798781a1f8bda7 100644 (file)
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -684,15 +684,12 @@ restart:
                        case NETDEV_RELEASE:
                        case NETDEV_JOIN:
                        case NETDEV_UNREGISTER:
-                               /*
-                                * rtnl_lock already held
+                               /* rtnl_lock already held
                                 * we might sleep in __netpoll_cleanup()
                                 */
                                spin_unlock_irqrestore(&target_list_lock, flags);
 
-                               mutex_lock(&nt->mutex);
                                __netpoll_cleanup(&nt->np);
-                               mutex_unlock(&nt->mutex);
 
                                spin_lock_irqsave(&target_list_lock, flags);
                                dev_put(nt->np.dev);