net: sched: add helper function to take reference to Qdisc

[ Upstream commit 9d7e82cec35c027756ec97e274f878251f271181 ]

Implement function to take reference to Qdisc that relies on rcu read lock
instead of rtnl mutex. Function only takes reference to Qdisc if reference
counter isn't zero. Intended to be used by unlocked cls API.

Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[Lee: Sent to Stable]
Link: https://syzkaller.appspot.com/bug?id=d7e411c5472dd5da33d8cc921ccadc747743a568
Reported-by: syzbot+5f229e48cccc804062c0@syzkaller.appspotmail.com
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index 04a5133d875e8f2b383dfd0cace759a0c19550de..c0147888b15553c595cada8ba05b7e2fd8239849 100644 (file)
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -118,6 +118,19 @@ static inline void qdisc_refcount_inc(struct Qdisc *qdisc)
        refcount_inc(&qdisc->refcnt);
 }
 
+/* Intended to be used by unlocked users, when concurrent qdisc release is
+ * possible.
+ */
+
+static inline struct Qdisc *qdisc_refcount_inc_nz(struct Qdisc *qdisc)
+{
+       if (qdisc->flags & TCQ_F_BUILTIN)
+               return qdisc;
+       if (refcount_inc_not_zero(&qdisc->refcnt))
+               return qdisc;
+       return NULL;
+}
+
 static inline bool qdisc_is_running(struct Qdisc *qdisc)
 {
        if (qdisc->flags & TCQ_F_NOLOCK)