netdev - [PATCH net-next v3 01/10] net: core: netlink: add helper refcount dec and lock function

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Message-Id: <1537806178-10944-2-git-send-email-vladbu@mellanox.com>
Date:   Mon, 24 Sep 2018 19:22:49 +0300
From:   Vlad Buslov <vladbu@...lanox.com>
To:     netdev@...r.kernel.org
Cc:     jhs@...atatu.com, xiyou.wangcong@...il.com, jiri@...nulli.us,
        davem@...emloft.net, stephen@...workplumber.org,
        ktkhai@...tuozzo.com, nicolas.dichtel@...nd.com,
        gregkh@...uxfoundation.org, mark.rutland@....com, leon@...nel.org,
        paulmck@...ux.vnet.ibm.com, fw@...len.de, dsahern@...il.com,
        christian@...uner.io, lucien.xin@...il.com,
        jakub.kicinski@...ronome.com, jbenc@...hat.com,
        Vlad Buslov <vladbu@...lanox.com>
Subject: [PATCH net-next v3 01/10] net: core: netlink: add helper refcount dec and lock function

Rtnl lock is encapsulated in netlink and cannot be accessed by other
modules directly. This means that reference counted objects that rely on
rtnl lock cannot use it with refcounter helper function that atomically
releases decrements reference and obtains mutex.

This patch implements simple wrapper function around refcount_dec_and_lock
that obtains rtnl lock if reference counter value reached 0.

Signed-off-by: Vlad Buslov <vladbu@...lanox.com>
Acked-by: Jiri Pirko <jiri@...lanox.com>
---
 include/linux/rtnetlink.h | 2 ++
 net/core/rtnetlink.c      | 6 ++++++
 2 files changed, 8 insertions(+)

diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
index 5225832bd6ff..9cdd76348d9a 100644
--- a/include/linux/rtnetlink.h
+++ b/include/linux/rtnetlink.h
@@ -6,6 +6,7 @@
 #include <linux/mutex.h>
 #include <linux/netdevice.h>
 #include <linux/wait.h>
+#include <linux/refcount.h>
 #include <uapi/linux/rtnetlink.h>
 
 extern int rtnetlink_send(struct sk_buff *skb, struct net *net, u32 pid, u32 group, int echo);
@@ -34,6 +35,7 @@ extern void rtnl_unlock(void);
 extern int rtnl_trylock(void);
 extern int rtnl_is_locked(void);
 extern int rtnl_lock_killable(void);
+extern bool refcount_dec_and_rtnl_lock(refcount_t *r);
 
 extern wait_queue_head_t netdev_unregistering_wq;
 extern struct rw_semaphore pernet_ops_rwsem;
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 80a7e18c65fb..35162e1b06ad 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -130,6 +130,12 @@ int rtnl_is_locked(void)
 }
 EXPORT_SYMBOL(rtnl_is_locked);
 
+bool refcount_dec_and_rtnl_lock(refcount_t *r)
+{
+	return refcount_dec_and_mutex_lock(r, &rtnl_mutex);
+}
+EXPORT_SYMBOL(refcount_dec_and_rtnl_lock);
+
 #ifdef CONFIG_PROVE_LOCKING
 bool lockdep_rtnl_is_held(void)
 {
-- 
2.7.5