netdev - [PATCH net-next v2 3/6] rtnetlink: add helper to dump qdisc name

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Message-Id: <20170922061008.14723-4-fw@strlen.de>
Date:   Fri, 22 Sep 2017 08:10:05 +0200
From:   Florian Westphal <fw@...len.de>
To:     <netdev@...r.kernel.org>
Cc:     Florian Westphal <fw@...len.de>
Subject: [PATCH net-next v2 3/6] rtnetlink: add helper to dump qdisc name

We can use rcu here to make this safe even if we would not hold rtnl:
qdisc_destroy uses call_rcu to free the Qdisc struct.

Signed-off-by: Florian Westphal <fw@...len.de>
---
 net/core/rtnetlink.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index c801212ee40e..ad3f27da37a8 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1332,6 +1332,19 @@ static int nla_put_iflink(struct sk_buff *skb, const struct net_device *dev)
 	return nla_put_u32(skb, IFLA_LINK, ifindex);
 }
 
+static int nla_put_qdisc(struct sk_buff *skb, struct net_device *dev)
+{
+	struct Qdisc *q;
+	int ret = 0;
+
+	rcu_read_lock();
+	q = READ_ONCE(dev->qdisc);
+	if (q)
+		ret = nla_put_string(skb, IFLA_QDISC, q->ops->id);
+	rcu_read_unlock();
+	return ret;
+}
+
 static int rtnl_fill_ifinfo(struct sk_buff *skb, struct net_device *dev,
 			    int type, u32 pid, u32 seq, u32 change,
 			    unsigned int flags, u32 ext_filter_mask,
@@ -1372,8 +1385,7 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb, struct net_device *dev,
 	    nla_put_iflink(skb, dev) ||
 	    put_master_ifindex(skb, dev) ||
 	    nla_put_u8(skb, IFLA_CARRIER, netif_carrier_ok(dev)) ||
-	    (dev->qdisc &&
-	     nla_put_string(skb, IFLA_QDISC, dev->qdisc->ops->id)) ||
+	    nla_put_qdisc(skb, dev) ||
 	    (dev->ifalias &&
 	     nla_put_string(skb, IFLA_IFALIAS, dev->ifalias)) ||
 	    nla_put_u32(skb, IFLA_CARRIER_CHANGES,
-- 
2.13.5