[PATCH v2 net-next 4/7] rtnetlink: small rtnl lock pushdown

[Florian Westphal]

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 <f...@strlen.de>
Reviewed-by: Hannes Frederic Sowa <han...@stressinduktion.org>
---
 No changes since v1.
 net/core/rtnetlink.c | 19 +++++++++++++------
 1 file 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)
-- 
2.13.0