ppp: set qdisc_tx_busylock to avoid LOCKDEP splat

If a qdisc is installed on a ppp device, its possible to get
a lockdep splat under stress, because nested dev_queue_xmit() can
lock busylock a second time (on a different device, so its a false
positive)

Avoid this problem using a distinct lock_class_key for ppp
devices.

Reported-by: Yanko Kaneti <yaneti@declera.com>
Tested-by: Yanko Kaneti <yaneti@declera.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 0 deletions

diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
index 4fd754e74eb2..3db9131e9229 100644
--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -1058,7 +1058,15 @@ ppp_get_stats64(struct net_device *dev, struct rtnl_link_stats64 *stats64)
         return stats64;
 }
 
+static struct lock_class_key ppp_tx_busylock;
+static int ppp_dev_init(struct net_device *dev)
+{
+        dev->qdisc_tx_busylock = &ppp_tx_busylock;
+        return 0;
+}
+
 static const struct net_device_ops ppp_netdev_ops = {
+        .ndo_init        = ppp_dev_init,
         .ndo_start_xmit  = ppp_start_xmit,
         .ndo_do_ioctl    = ppp_net_ioctl,
         .ndo_get_stats64 = ppp_get_stats64,