rtnetlink: small rtnl lock pushdown

instead of rtnl lock/unload at the top level, push it down
to the called function.

This is just an intermediate step, next commit switches protection
of the rtnl_link ops table to rcu, in which case (for dumps) the
rtnl lock is acquired only by the netlink dumper infrastructure
(current lock/unlock/dump/lock/unlock rtnl sequence becomes
 rcu lock/rcu unlock/dump).

Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 13 insertions, 6 deletions

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index c45a7c5e3232..be01d8e48661 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -4178,9 +4178,11 @@ static int rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
                 rtnl_dumpit_func dumpit;
                 u16 min_dump_alloc = 0;
 
+                rtnl_lock();
+
                 dumpit = rtnl_get_dumpit(family, type);
                 if (dumpit == NULL)
-                        return -EOPNOTSUPP;
+                        goto err_unlock;
 
                 refcount_inc(&rtnl_msg_handlers_ref[family]);
 
@@ -4196,23 +4198,28 @@ static int rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
                         };
                         err = netlink_dump_start(rtnl, skb, nlh, &c);
                 }
-                rtnl_lock();
                 refcount_dec(&rtnl_msg_handlers_ref[family]);
                 return err;
         }
 
+        rtnl_lock();
         doit = rtnl_get_doit(family, type);
         if (doit == NULL)
-                return -EOPNOTSUPP;
+                goto err_unlock;
 
-        return doit(skb, nlh, extack);
+        err = doit(skb, nlh, extack);
+        rtnl_unlock();
+
+        return err;
+
+err_unlock:
+        rtnl_unlock();
+        return -EOPNOTSUPP;
 }
 
 static void rtnetlink_rcv(struct sk_buff *skb)
 {
-        rtnl_lock();
         netlink_rcv_skb(skb, &rtnetlink_rcv_msg);
-        rtnl_unlock();
 }
 
 static int rtnetlink_bind(struct net *net, int group)