rtnetlink: do not depend on RTNL for IFLA_QDISC output

dev->qdisc can be read using RCU protection.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 28050e53ecb025f8d207f4b38805fb108799ca65..ba5301d6df849d7d0c4c79989ba4fc68a5758df0 100644 (file)
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1832,7 +1832,6 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb,
        if (tgt_netnsid >= 0 && nla_put_s32(skb, IFLA_TARGET_NETNSID, tgt_netnsid))
                goto nla_put_failure;
 
-       qdisc = rtnl_dereference(dev->qdisc);
        if (nla_put_string(skb, IFLA_IFNAME, dev->name) ||
            nla_put_u32(skb, IFLA_TXQLEN, dev->tx_queue_len) ||
            nla_put_u8(skb, IFLA_OPERSTATE,
@@ -1857,8 +1856,6 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb,
 #endif
            put_master_ifindex(skb, dev) ||
            nla_put_u8(skb, IFLA_CARRIER, netif_carrier_ok(dev)) ||
-           (qdisc &&
-            nla_put_string(skb, IFLA_QDISC, qdisc->ops->id)) ||
            nla_put_ifalias(skb, dev) ||
            nla_put_u32(skb, IFLA_CARRIER_CHANGES,
                        atomic_read(&dev->carrier_up_count) +
@@ -1924,6 +1921,9 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb,
                goto nla_put_failure;
 
        rcu_read_lock();
+       qdisc = rcu_dereference(dev->qdisc);
+       if (qdisc && nla_put_string(skb, IFLA_QDISC, qdisc->ops->id))
+               goto nla_put_failure_rcu;
        if (rtnl_fill_link_af(skb, dev, ext_filter_mask))
                goto nla_put_failure_rcu;
        if (rtnl_fill_link_ifmap(skb, dev))