genl: Fix genl dumpit() locking.

In case of genl-family with parallel ops off, dumpif() callback
is expected to run under genl_lock, But commit def31174
(genl: Allow concurrent genl callbacks.) changed this behaviour
where only first dumpit() op was called under genl-lock.
For subsequent dump, only nlk->cb_lock was taken.
Following patch fixes it by defining locked dumpit() and done()
callback which takes care of genl-locking.

CC: Jesse Gross <jesse@nicira.com>
CC: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/netlink/genetlink.c

@@ -544,6 +544,30 @@ void *genlmsg_put(struct sk_buff *skb, u32 portid, u32 seq,
 }
 EXPORT_SYMBOL(genlmsg_put);
 
+static int genl_lock_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
+{
+	struct genl_ops *ops = cb->data;
+	int rc;
+
+	genl_lock();
+	rc = ops->dumpit(skb, cb);
+	genl_unlock();
+	return rc;
+}
+
+static int genl_lock_done(struct netlink_callback *cb)
+{
+	struct genl_ops *ops = cb->data;
+	int rc = 0;
+
+	if (ops->done) {
+		genl_lock();
+		rc = ops->done(cb);
+		genl_unlock();
+	}
+	return rc;
+}
+
 static int genl_family_rcv_msg(struct genl_family *family,
 			       struct sk_buff *skb,
 			       struct nlmsghdr *nlh)
@@ -572,15 +596,32 @@ static int genl_family_rcv_msg(struct genl_family *family,
 		return -EPERM;
 
 	if ((nlh->nlmsg_flags & NLM_F_DUMP) == NLM_F_DUMP) {
+		int rc;
+
+		if (ops->dumpit == NULL)
+			return -EOPNOTSUPP;
+
+		if (!family->parallel_ops) {
+			struct netlink_dump_control c = {
+				.data = ops,
+				.dump = genl_lock_dumpit,
+				.done = genl_lock_done,
+			};
+
+			genl_unlock();
+			rc = netlink_dump_start(net->genl_sock, skb, nlh, &c);
+			genl_lock();
+
+		} else {
 			struct netlink_dump_control c = {
 				.dump = ops->dumpit,
 				.done = ops->done,
 			};
 
-		if (ops->dumpit == NULL)
-			return -EOPNOTSUPP;
+			rc = netlink_dump_start(net->genl_sock, skb, nlh, &c);
+		}
 
-		return netlink_dump_start(net->genl_sock, skb, nlh, &c);
+		return rc;
 	}
 
 	if (ops->doit == NULL)