pkt_sched: Add lockdep annotation for qdisc locks

Qdisc locks are initialized in the same function, qdisc_alloc(), so
lockdep can't distinguish tx qdisc lock from rx and reports "possible
recursive locking detected" when both these locks are taken eg. while
using act_mirred with ifb. This looks like a false positive. Anyway,
after this patch these locks will be reported more exactly.

Reported-by: Denys Fedoryshchenko <denys@visp.net.lb>
Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_api.c

@@ -27,6 +27,7 @@
 #include <linux/kmod.h>
 #include <linux/list.h>
 #include <linux/hrtimer.h>
+#include <linux/lockdep.h>
 
 #include <net/net_namespace.h>
 #include <net/sock.h>
@@ -707,6 +708,10 @@ static int qdisc_graft(struct net_device *dev, struct Qdisc *parent,
 	return err;
 }
 
+/* lockdep annotation is needed for ingress; egress gets it only for name */
+static struct lock_class_key qdisc_tx_lock;
+static struct lock_class_key qdisc_rx_lock;
+
 /*
    Allocate and initialize new qdisc.
 
@@ -767,6 +772,7 @@ qdisc_create(struct net_device *dev, struct netdev_queue *dev_queue,
 	if (handle == TC_H_INGRESS) {
 		sch->flags |= TCQ_F_INGRESS;
 		handle = TC_H_MAKE(TC_H_INGRESS, 0);
+		lockdep_set_class(qdisc_lock(sch), &qdisc_rx_lock);
 	} else {
 		if (handle == 0) {
 			handle = qdisc_alloc_handle(dev);
@@ -774,6 +780,7 @@ qdisc_create(struct net_device *dev, struct netdev_queue *dev_queue,
 			if (handle == 0)
 				goto err_out3;
 		}
+		lockdep_set_class(qdisc_lock(sch), &qdisc_tx_lock);
 	}
 
 	sch->handle = handle;