batman-adv: Avoid deadlock between rtnl_lock and s_active

The hard_if_event is called by the notifier with rtnl_lock and tries to
remove sysfs entries when a NETDEV_UNREGISTER event is received. This
will automatically take the s_active lock.

The s_active lock is also used when a new interface is added to a meshif
through sysfs. In that situation we cannot wait for the rntl_lock before
creating the actual batman-adv interface to prevent a deadlock. It is
still possible to try to get the rtnl_lock and immediately abort the
current operation when the trylock call failed.

Signed-off-by: Sven Eckelmann <sven@narfation.org>

diff --git a/net/batman-adv/bat_sysfs.c b/net/batman-adv/bat_sysfs.c
index 85ba20d..497a070 100644 (file)
--- a/net/batman-adv/bat_sysfs.c
+++ b/net/batman-adv/bat_sysfs.c
@@ -488,24 +488,24 @@ static ssize_t store_mesh_iface(struct kobject *kobj, struct attribute *attr,
            (strncmp(hard_iface->soft_iface->name, buff, IFNAMSIZ) == 0))
                goto out;
 
+       if (!rtnl_trylock()) {
+               ret = -ERESTARTSYS;
+               goto out;
+       }
+
        if (status_tmp == IF_NOT_IN_USE) {
-               rtnl_lock();
                hardif_disable_interface(hard_iface);
-               rtnl_unlock();
-               goto out;
+               goto unlock;
        }
 
        /* if the interface already is in use */
-       if (hard_iface->if_status != IF_NOT_IN_USE) {
-               rtnl_lock();
+       if (hard_iface->if_status != IF_NOT_IN_USE)
                hardif_disable_interface(hard_iface);
-               rtnl_unlock();
-       }
 
-       rtnl_lock();
        ret = hardif_enable_interface(hard_iface, buff);
-       rtnl_unlock();
 
+unlock:
+       rtnl_unlock();
 out:
        hardif_free_ref(hard_iface);
        return ret;