[PATCH net-next 1/2] net: bridge: switchdev: add br_switchdev_fdb_find_port()

[Julius Bairaktaris]

Add an RCU lookup that returns the port of a non-local FDB entry that
switchdev is notified of: not locked, not added by the user as a
dynamic entry, and not learned by a switchdev driver.

A switchdev driver that handles FDB events from a workqueue cannot take
RTNL for br_fdb_find_port(), and has to ignore the entries whose
deletion it will not be notified of. The filter of
br_switchdev_fdb_notify() moves into a helper that both use, with no
functional change; the learning path does not change.

Signed-off-by: Julius Bairaktaris <julius@xxxxxxxxxxxxxx>
---
 include/linux/if_bridge.h | 13 ++++++++
 net/bridge/br_switchdev.c | 63 +++++++++++++++++++++++++++++++++------
 2 files changed, 67 insertions(+), 9 deletions(-)

diff --git a/include/linux/if_bridge.h b/include/linux/if_bridge.h
index 75673b8bffcb8..e050b7e698fc9 100644
--- a/include/linux/if_bridge.h
+++ b/include/linux/if_bridge.h
@@ -201,6 +201,19 @@ static inline int br_mst_get_state(const struct net_device *dev, u16 msti,
 }
 #endif
 
+#if IS_ENABLED(CONFIG_BRIDGE) && IS_ENABLED(CONFIG_NET_SWITCHDEV)
+struct net_device *br_switchdev_fdb_find_port(const struct net_device *br_dev,
+					      const unsigned char *addr,
+					      u16 vid);
+#else
+static inline struct net_device *
+br_switchdev_fdb_find_port(const struct net_device *br_dev,
+			   const unsigned char *addr, u16 vid)
+{
+	return NULL;
+}
+#endif
+
 #if IS_ENABLED(CONFIG_BRIDGE)
 struct net_device *br_fdb_find_port(const struct net_device *br_dev,
 				    const unsigned char *addr,
diff --git a/net/bridge/br_switchdev.c b/net/bridge/br_switchdev.c
index 10f3aea6a1f82..02ca1cbcfede0 100644
--- a/net/bridge/br_switchdev.c
+++ b/net/bridge/br_switchdev.c
@@ -141,14 +141,10 @@ static void br_switchdev_fdb_populate(struct net_bridge *br,
 	item->info.ctx = ctx;
 }
 
-void
-br_switchdev_fdb_notify(struct net_bridge *br,
-			const struct net_bridge_fdb_entry *fdb, int type)
+static bool br_switchdev_fdb_notifies(const struct net_bridge_fdb_entry *fdb)
 {
-	struct switchdev_notifier_fdb_info item;
-
 	if (test_bit(BR_FDB_LOCKED, &fdb->flags))
-		return;
+		return false;
 
 	/* Entries with these flags were created using ndm_state == NUD_REACHABLE,
 	 * ndm_flags == NTF_MASTER( | NTF_STICKY), ext_flags == 0 by something
@@ -156,9 +152,58 @@ br_switchdev_fdb_notify(struct net_bridge *br,
 	 * Drivers don't know how to deal with these, so don't notify them to
 	 * avoid confusing them.
 	 */
-	if (test_bit(BR_FDB_ADDED_BY_USER, &fdb->flags) &&
-	    !test_bit(BR_FDB_STATIC, &fdb->flags) &&
-	    !test_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags))
+	return !test_bit(BR_FDB_ADDED_BY_USER, &fdb->flags) ||
+	       test_bit(BR_FDB_STATIC, &fdb->flags) ||
+	       test_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags);
+}
+
+/**
+ * br_switchdev_fdb_find_port - find the port of an entry switchdev knows of
+ * @br_dev: the bridge device
+ * @addr: the MAC address of the entry
+ * @vid: the VLAN of the entry
+ *
+ * Must be called under RCU; the device is valid until the read-side critical
+ * section ends.
+ *
+ * Return: the port of the non-local entry for @addr and @vid, or NULL if
+ * there is none or switchdev is not notified of it.
+ */
+struct net_device *br_switchdev_fdb_find_port(const struct net_device *br_dev,
+					      const unsigned char *addr,
+					      u16 vid)
+{
+	const struct net_bridge_port *p;
+	struct net_bridge_fdb_entry *f;
+
+	RCU_LOCKDEP_WARN(!rcu_read_lock_held(), "suspicious use outside RCU");
+
+	if (!netif_is_bridge_master(br_dev))
+		return NULL;
+
+	f = br_fdb_find_rcu(netdev_priv(br_dev), addr, vid);
+	if (!f || test_bit(BR_FDB_LOCAL, &f->flags) ||
+	    !br_switchdev_fdb_notifies(f))
+		return NULL;
+
+	/* learned by a switchdev driver, which is not notified back */
+	if (test_bit(BR_FDB_ADDED_BY_EXT_LEARN, &f->flags) &&
+	    !test_bit(BR_FDB_ADDED_BY_USER, &f->flags))
+		return NULL;
+
+	p = br_fdb_dst_port(f);
+
+	return p ? p->dev : NULL;
+}
+EXPORT_SYMBOL_GPL(br_switchdev_fdb_find_port);
+
+void
+br_switchdev_fdb_notify(struct net_bridge *br,
+			const struct net_bridge_fdb_entry *fdb, int type)
+{
+	struct switchdev_notifier_fdb_info item;
+
+	if (!br_switchdev_fdb_notifies(fdb))
 		return;
 
 	br_switchdev_fdb_populate(br, &item, fdb, NULL);
-- 
2.53.0