[PATCH v2 net-next 6/7] rtnetlink: add RTNL_FLAG_DOIT_UNLOCKED

[Florian Westphal]

Allow callers to tell rtnetlink core that its doit callback
should be invoked without holding rtnl mutex.

Signed-off-by: Florian Westphal <f...@strlen.de>
Reviewed-by: Hannes Frederic Sowa <han...@stressinduktion.org>
---
 change since v1: don't make ipv6 route rtnl handlers lockless

 include/net/rtnetlink.h |  4 ++++
 net/core/rtnetlink.c    | 15 +++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/include/net/rtnetlink.h b/include/net/rtnetlink.h
index ac32460a0adb..21837ca68ecc 100644
--- a/include/net/rtnetlink.h
+++ b/include/net/rtnetlink.h
@@ -8,6 +8,10 @@ typedef int (*rtnl_doit_func)(struct sk_buff *, struct 
nlmsghdr *,
                              struct netlink_ext_ack *);
 typedef int (*rtnl_dumpit_func)(struct sk_buff *, struct netlink_callback *);
 
+enum rtnl_link_flags {
+       RTNL_FLAG_DOIT_UNLOCKED = 1,
+};
+
 int __rtnl_register(int protocol, int msgtype,
                    rtnl_doit_func, rtnl_dumpit_func, unsigned int flags);
 void rtnl_register(int protocol, int msgtype,
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index d45946177bc8..dd4e50dfa248 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -62,6 +62,7 @@
 struct rtnl_link {
        rtnl_doit_func          doit;
        rtnl_dumpit_func        dumpit;
+       unsigned int            flags;
 };
 
 static DEFINE_MUTEX(rtnl_mutex);
@@ -184,6 +185,7 @@ int __rtnl_register(int protocol, int msgtype,
                tab[msgindex].doit = doit;
        if (dumpit)
                tab[msgindex].dumpit = dumpit;
+       tab[msgindex].flags |= flags;
 
        return 0;
 }
@@ -233,6 +235,7 @@ int rtnl_unregister(int protocol, int msgtype)
 
        handlers[msgindex].doit = NULL;
        handlers[msgindex].dumpit = NULL;
+       handlers[msgindex].flags = 0;
        rtnl_unlock();
 
        return 0;
@@ -4143,6 +4146,7 @@ static int rtnetlink_rcv_msg(struct sk_buff *skb, struct 
nlmsghdr *nlh,
        struct rtnl_link *handlers;
        int err = -EOPNOTSUPP;
        rtnl_doit_func doit;
+       unsigned int flags;
        int kind;
        int family;
        int type;
@@ -4209,6 +4213,17 @@ static int rtnetlink_rcv_msg(struct sk_buff *skb, struct 
nlmsghdr *nlh,
                return err;
        }
 
+       flags = READ_ONCE(handlers[type].flags);
+       if (flags & RTNL_FLAG_DOIT_UNLOCKED) {
+               refcount_inc(&rtnl_msg_handlers_ref[family]);
+               doit = READ_ONCE(handlers[type].doit);
+               rcu_read_unlock();
+               if (doit)
+                       err = doit(skb, nlh, extack);
+               refcount_dec(&rtnl_msg_handlers_ref[family]);
+               return err;
+       }
+
        rcu_read_unlock();
 
        rtnl_lock();
-- 
2.13.0