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 dcb2134..adeee61 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -684,15 +684,12 @@
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);