netdev - [RFC PATCH net-next 08/10] net: dsa: introduce a robust form of MTU cross-chip notifiers

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Date:   Thu, 18 Aug 2022 18:49:09 +0300
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     netdev@...r.kernel.org
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [RFC PATCH net-next 08/10] net: dsa: introduce a robust form of MTU cross-chip notifiers

Add rollback to the MTU cross-chip change procedure, which allows us to
leave the tree in a consistent state at all times.

Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
 net/dsa/dsa_priv.h |  3 ++-
 net/dsa/port.c     | 19 +++++++++++++++++--
 net/dsa/slave.c    |  7 ++++---
 3 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/net/dsa/dsa_priv.h b/net/dsa/dsa_priv.h
index b4545b9ebb64..6c935f151864 100644
--- a/net/dsa/dsa_priv.h
+++ b/net/dsa/dsa_priv.h
@@ -230,7 +230,8 @@ int dsa_port_mst_enable(struct dsa_port *dp, bool on,
 			struct netlink_ext_ack *extack);
 int dsa_port_vlan_msti(struct dsa_port *dp,
 		       const struct switchdev_vlan_msti *msti);
-int dsa_port_mtu_change(struct dsa_port *dp, int new_mtu);
+void dsa_port_mtu_change(struct dsa_port *dp, int new_mtu);
+int dsa_port_mtu_change_robust(struct dsa_port *dp, int new_mtu, int old_mtu);
 int dsa_port_fdb_add(struct dsa_port *dp, const unsigned char *addr,
 		     u16 vid);
 int dsa_port_fdb_del(struct dsa_port *dp, const unsigned char *addr,
diff --git a/net/dsa/port.c b/net/dsa/port.c
index 2fec3df65643..4095592c4790 100644
--- a/net/dsa/port.c
+++ b/net/dsa/port.c
@@ -962,14 +962,29 @@ int dsa_port_vlan_msti(struct dsa_port *dp,
 	return ds->ops->vlan_msti_set(ds, *dp->bridge, msti);
 }
 
-int dsa_port_mtu_change(struct dsa_port *dp, int new_mtu)
+void dsa_port_mtu_change(struct dsa_port *dp, int new_mtu)
 {
 	struct dsa_notifier_mtu_info info = {
 		.dp = dp,
 		.mtu = new_mtu,
 	};
 
-	return dsa_port_notify(dp, DSA_NOTIFIER_MTU, &info);
+	dsa_port_notify(dp, DSA_NOTIFIER_MTU, &info);
+}
+
+int dsa_port_mtu_change_robust(struct dsa_port *dp, int new_mtu, int old_mtu)
+{
+	struct dsa_notifier_mtu_info old_info = {
+		.dp = dp,
+		.mtu = old_mtu,
+	};
+	struct dsa_notifier_mtu_info info = {
+		.dp = dp,
+		.mtu = new_mtu,
+	};
+
+	return dsa_port_notify_robust(dp, DSA_NOTIFIER_MTU, &info,
+				      DSA_NOTIFIER_MTU, &old_info);
 }
 
 int dsa_port_fdb_add(struct dsa_port *dp, const unsigned char *addr,
diff --git a/net/dsa/slave.c b/net/dsa/slave.c
index ad6a6663feeb..02cc1774888a 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c
@@ -1810,6 +1810,7 @@ int dsa_slave_change_mtu(struct net_device *dev, int new_mtu)
 	int largest_mtu = 0;
 	int new_master_mtu;
 	int old_master_mtu;
+	int old_cpu_mtu;
 	int mtu_limit;
 	int cpu_mtu;
 	int err;
@@ -1849,6 +1850,7 @@ int dsa_slave_change_mtu(struct net_device *dev, int new_mtu)
 	 * MTU, since that surely isn't either.
 	 */
 	cpu_mtu = largest_mtu;
+	old_cpu_mtu = old_master_mtu - dsa_tag_protocol_overhead(cpu_dp->tag_ops);
 
 	/* Start applying stuff */
 	if (new_master_mtu != old_master_mtu) {
@@ -1859,7 +1861,7 @@ int dsa_slave_change_mtu(struct net_device *dev, int new_mtu)
 		/* We only need to propagate the MTU of the CPU port to
 		 * upstream switches, so emit a notifier which updates them.
 		 */
-		err = dsa_port_mtu_change(cpu_dp, cpu_mtu);
+		err = dsa_port_mtu_change_robust(cpu_dp, cpu_mtu, old_cpu_mtu);
 		if (err)
 			goto out_cpu_failed;
 	}
@@ -1876,8 +1878,7 @@ int dsa_slave_change_mtu(struct net_device *dev, int new_mtu)
 
 out_port_failed:
 	if (new_master_mtu != old_master_mtu)
-		dsa_port_mtu_change(cpu_dp, old_master_mtu -
-				    dsa_tag_protocol_overhead(cpu_dp->tag_ops));
+		dsa_port_mtu_change(cpu_dp, old_cpu_mtu);
 out_cpu_failed:
 	if (new_master_mtu != old_master_mtu)
 		dev_set_mtu(master, old_master_mtu);
-- 
2.34.1