linux-kernel - [PATCH 4.19 13/74] net: sched: add helper function to take reference to Qdisc

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Date:   Mon, 13 Dec 2021 10:29:44 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org, lee.jones@...aro.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Vlad Buslov <vladbu@...lanox.com>,
        Jiri Pirko <jiri@...lanox.com>,
        "David S. Miller" <davem@...emloft.net>,
        syzbot+5f229e48cccc804062c0@...kaller.appspotmail.com
Subject: [PATCH 4.19 13/74] net: sched: add helper function to take reference to Qdisc

From: Vlad Buslov <vladbu@...lanox.com>

[ 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@...lanox.com>
Acked-by: Jiri Pirko <jiri@...lanox.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
[Lee: Sent to Stable]
Link: https://syzkaller.appspot.com/bug?id=d7e411c5472dd5da33d8cc921ccadc747743a568
Reported-by: syzbot+5f229e48cccc804062c0@...kaller.appspotmail.com
Signed-off-by: Lee Jones <lee.jones@...aro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 include/net/sch_generic.h |   13 +++++++++++++
 1 file changed, 13 insertions(+)

--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -118,6 +118,19 @@ static inline void qdisc_refcount_inc(st
 	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)