netdev - [RFC PATCH net-next 6/7] net: dsa: hold rtnl_mutex when calling dsa_master

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Date:   Thu,  9 Dec 2021 00:32:29 +0200
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Ansuel Smith <ansuelsmth@...il.com>
Subject: [RFC PATCH net-next 6/7] net: dsa: hold rtnl_mutex when calling dsa_master_{setup,teardown}

DSA needs to simulate master tracking events when a binding is first
with a DSA master established and torn down, in order to give drivers
the simplifying guarantee that ->master_up and ->master_going_down calls
are made in exactly this order. To avoid races, we need to block the
reception of NETDEV_UP/NETDEV_GOING_DOWN events in the netdev notifier
chain while we are changing the master's dev->dsa_ptr (this changes what
netdev_uses_dsa(dev) reports).

The dsa_master_setup() and dsa_master_teardown() functions optionally
require the rtnl_mutex to be held, if the tagger needs the master to be
promiscuous, these functions call dev_set_promiscuity(). Move the
rtnl_lock() from that function and make it top-level.

Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
 net/dsa/dsa2.c   | 8 ++++++++
 net/dsa/master.c | 4 ++--
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/net/dsa/dsa2.c b/net/dsa/dsa2.c
index fe3a3d05ee24..dc104023d351 100644
--- a/net/dsa/dsa2.c
+++ b/net/dsa/dsa2.c
@@ -1015,6 +1015,8 @@ static int dsa_tree_setup_master(struct dsa_switch_tree *dst)
 	struct dsa_port *dp;
 	int err;
 
+	rtnl_lock();
+
 	list_for_each_entry(dp, &dst->ports, list) {
 		if (dsa_port_is_cpu(dp)) {
 			err = dsa_master_setup(dp->master, dp);
@@ -1023,6 +1025,8 @@ static int dsa_tree_setup_master(struct dsa_switch_tree *dst)
 		}
 	}
 
+	rtnl_unlock();
+
 	return 0;
 }
 
@@ -1030,9 +1034,13 @@ static void dsa_tree_teardown_master(struct dsa_switch_tree *dst)
 {
 	struct dsa_port *dp;
 
+	rtnl_lock();
+
 	list_for_each_entry(dp, &dst->ports, list)
 		if (dsa_port_is_cpu(dp))
 			dsa_master_teardown(dp->master);
+
+	rtnl_unlock();
 }
 
 static int dsa_tree_setup_lags(struct dsa_switch_tree *dst)
diff --git a/net/dsa/master.c b/net/dsa/master.c
index f4efb244f91d..2199104ca7df 100644
--- a/net/dsa/master.c
+++ b/net/dsa/master.c
@@ -267,9 +267,9 @@ static void dsa_master_set_promiscuity(struct net_device *dev, int inc)
 	if (!ops->promisc_on_master)
 		return;
 
-	rtnl_lock();
+	ASSERT_RTNL();
+
 	dev_set_promiscuity(dev, inc);
-	rtnl_unlock();
 }
 
 static ssize_t tagging_show(struct device *d, struct device_attribute *attr,
-- 
2.25.1