net: dsa: keep the bridge_dev and bridge_num as part of the same structure

The main desire behind this is to provide coherent bridge information to
the fast path without locking.

For example, right now we set dp->bridge_dev and dp->bridge_num from
separate code paths, it is theoretically possible for a packet
transmission to read these two port properties consecutively and find a
bridge number which does not correspond with the bridge device.

Another desire is to start passing more complex bridge information to
dsa_switch_ops functions. For example, with FDB isolation, it is
expected that drivers will need to be passed the bridge which requested
an FDB/MDB entry to be offloaded, and along with that bridge_dev, the
associated bridge_num should be passed too, in case the driver might
want to implement an isolation scheme based on that number.

We already pass the {bridge_dev, bridge_num} pair to the TX forwarding
offload switch API, however we'd like to remove that and squash it into
the basic bridge join/leave API. So that means we need to pass this
pair to the bridge join/leave API.

During dsa_port_bridge_leave, first we unset dp->bridge_dev, then we
call the driver's .port_bridge_leave with what used to be our
dp->bridge_dev, but provided as an argument.

When bridge_dev and bridge_num get folded into a single structure, we
need to preserve this behavior in dsa_port_bridge_leave: we need a copy
of what used to be in dp->bridge.

Switch drivers check bridge membership by comparing dp->bridge_dev with
the provided bridge_dev, but now, if we provide the struct dsa_bridge as
a pointer, they cannot keep comparing dp->bridge to the provided
pointer, since this only points to an on-stack copy. To make this
obvious and prevent driver writers from forgetting and doing stupid
things, in this new API, the struct dsa_bridge is provided as a full
structure (not very large, contains an int and a pointer) instead of a
pointer. An explicit comparison function needs to be used to determine
bridge membership: dsa_port_offloads_bridge().

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 29 insertions, 14 deletions

diff --git a/net/dsa/dsa2.c b/net/dsa/dsa2.c
index 4901cdc264ee..8814fa0e44c8 100644
--- a/net/dsa/dsa2.c
+++ b/net/dsa/dsa2.c
@@ -129,20 +129,29 @@ void dsa_lag_unmap(struct dsa_switch_tree *dst, struct net_device *lag)
 	}
 }
 
+struct dsa_bridge *dsa_tree_bridge_find(struct dsa_switch_tree *dst,
+					const struct net_device *br)
+{
+	struct dsa_port *dp;
+
+	list_for_each_entry(dp, &dst->ports, list)
+		if (dsa_port_bridge_dev_get(dp) == br)
+			return dp->bridge;
+
+	return NULL;
+}
+
 static int dsa_bridge_num_find(const struct net_device *bridge_dev)
 {
 	struct dsa_switch_tree *dst;
-	struct dsa_port *dp;
 
-	/* When preparing the offload for a port, it will have a valid
-	 * dp->bridge_dev pointer but a not yet valid dp->bridge_num.
-	 * However there might be other ports having the same dp->bridge_dev
-	 * and a valid dp->bridge_num, so just ignore this port.
-	 */
-	list_for_each_entry(dst, &dsa_tree_list, list)
-		list_for_each_entry(dp, &dst->ports, list)
-			if (dp->bridge_dev == bridge_dev && dp->bridge_num)
-				return dp->bridge_num;
+	list_for_each_entry(dst, &dsa_tree_list, list) {
+		struct dsa_bridge *bridge;
+
+		bridge = dsa_tree_bridge_find(dst, bridge_dev);
+		if (bridge)
+			return bridge->num;
+	}
 
 	return 0;
 }
@@ -151,6 +160,12 @@ unsigned int dsa_bridge_num_get(const struct net_device *bridge_dev, int max)
 {
 	unsigned int bridge_num = dsa_bridge_num_find(bridge_dev);
 
+	/* Switches without FDB isolation support don't get unique
+	 * bridge numbering
+	 */
+	if (!max)
+		return 0;
+
 	if (!bridge_num) {
 		/* First port that requests FDB isolation or TX forwarding
 		 * offload for this bridge
@@ -170,11 +185,11 @@ unsigned int dsa_bridge_num_get(const struct net_device *bridge_dev, int max)
 void dsa_bridge_num_put(const struct net_device *bridge_dev,
 			unsigned int bridge_num)
 {
-	/* Check if the bridge is still in use, otherwise it is time
-	 * to clean it up so we can reuse this bridge_num later.
+	/* Since we refcount bridges, we know that when we call this function
+	 * it is no longer in use, so we can just go ahead and remove it from
+	 * the bit mask.
 	 */
-	if (!dsa_bridge_num_find(bridge_dev))
-		clear_bit(bridge_num, &dsa_fwd_offloading_bridges);
+	clear_bit(bridge_num, &dsa_fwd_offloading_bridges);
 }
 
 struct dsa_switch *dsa_switch_find(int tree_index, int sw_index)