8021q: use RCU for egress QoS mappings

The TX fast path and reporting paths walk egress QoS mappings without
RTNL. Convert the mapping lists to RCU-protected pointers, use RCU
reader annotations in readers, and defer freeing mapping nodes with an
embedded rcu_head.

This prepares the egress QoS mapping code for safe removal of mapping
nodes in a follow-up change while preserving the current behavior.

Co-developed-by: Yuan Tan <yuantan098@gmail.com>
Signed-off-by: Yuan Tan <yuantan098@gmail.com>
Signed-off-by: Longxuan Yu <ylong030@ucr.edu>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Link: https://patch.msgid.link/9136768189f8c6d3f824f476c62d2fa1111688e8.1776647968.git.yuantan098@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

3 files changed, 30 insertions, 23 deletions

diff --git a/net/8021q/vlan_dev.c b/net/8021q/vlan_dev.c
index c40f7d5c4fca..a5340932b657 100644
--- a/net/8021q/vlan_dev.c
+++ b/net/8021q/vlan_dev.c
@@ -172,39 +172,34 @@ int vlan_dev_set_egress_priority(const struct net_device *dev,
 				 u32 skb_prio, u16 vlan_prio)
 {
 	struct vlan_dev_priv *vlan = vlan_dev_priv(dev);
-	struct vlan_priority_tci_mapping *mp = NULL;
+	struct vlan_priority_tci_mapping *mp;
 	struct vlan_priority_tci_mapping *np;
+	u32 bucket = skb_prio & 0xF;
 	u32 vlan_qos = (vlan_prio << VLAN_PRIO_SHIFT) & VLAN_PRIO_MASK;
 
 	/* See if a priority mapping exists.. */
-	mp = vlan->egress_priority_map[skb_prio & 0xF];
+	mp = rtnl_dereference(vlan->egress_priority_map[bucket]);
 	while (mp) {
 		if (mp->priority == skb_prio) {
 			if (mp->vlan_qos && !vlan_qos)
 				vlan->nr_egress_mappings--;
 			else if (!mp->vlan_qos && vlan_qos)
 				vlan->nr_egress_mappings++;
-			mp->vlan_qos = vlan_qos;
+			WRITE_ONCE(mp->vlan_qos, vlan_qos);
 			return 0;
 		}
-		mp = mp->next;
+		mp = rtnl_dereference(mp->next);
 	}
 
 	/* Create a new mapping then. */
-	mp = vlan->egress_priority_map[skb_prio & 0xF];
 	np = kmalloc_obj(struct vlan_priority_tci_mapping);
 	if (!np)
 		return -ENOBUFS;
 
-	np->next = mp;
 	np->priority = skb_prio;
 	np->vlan_qos = vlan_qos;
-	/* Before inserting this element in hash table, make sure all its fields
-	 * are committed to memory.
-	 * coupled with smp_rmb() in vlan_dev_get_egress_qos_mask()
-	 */
-	smp_wmb();
-	vlan->egress_priority_map[skb_prio & 0xF] = np;
+	RCU_INIT_POINTER(np->next, rtnl_dereference(vlan->egress_priority_map[bucket]));
+	rcu_assign_pointer(vlan->egress_priority_map[bucket], np);
 	if (vlan_qos)
 		vlan->nr_egress_mappings++;
 	return 0;
@@ -604,11 +599,17 @@ void vlan_dev_free_egress_priority(const struct net_device *dev)
 	int i;
 
 	for (i = 0; i < ARRAY_SIZE(vlan->egress_priority_map); i++) {
-		while ((pm = vlan->egress_priority_map[i]) != NULL) {
-			vlan->egress_priority_map[i] = pm->next;
-			kfree(pm);
+		pm = rtnl_dereference(vlan->egress_priority_map[i]);
+		RCU_INIT_POINTER(vlan->egress_priority_map[i], NULL);
+		while (pm) {
+			struct vlan_priority_tci_mapping *next;
+
+			next = rtnl_dereference(pm->next);
+			kfree_rcu(pm, rcu);
+			pm = next;
 		}
 	}
+	vlan->nr_egress_mappings = 0;
 }
 
 static void vlan_dev_uninit(struct net_device *dev)
diff --git a/net/8021q/vlan_netlink.c b/net/8021q/vlan_netlink.c
index a000b1ef0520..a5b16833e2ce 100644
--- a/net/8021q/vlan_netlink.c
+++ b/net/8021q/vlan_netlink.c
@@ -260,13 +260,15 @@ static int vlan_fill_info(struct sk_buff *skb, const struct net_device *dev)
 			goto nla_put_failure;
 
 		for (i = 0; i < ARRAY_SIZE(vlan->egress_priority_map); i++) {
-			for (pm = vlan->egress_priority_map[i]; pm;
-			     pm = pm->next) {
-				if (!pm->vlan_qos)
+			for (pm = rcu_dereference_rtnl(vlan->egress_priority_map[i]); pm;
+			     pm = rcu_dereference_rtnl(pm->next)) {
+				u16 vlan_qos = READ_ONCE(pm->vlan_qos);
+
+				if (!vlan_qos)
 					continue;
 
 				m.from = pm->priority;
-				m.to   = (pm->vlan_qos >> 13) & 0x7;
+				m.to   = (vlan_qos >> 13) & 0x7;
 				if (nla_put(skb, IFLA_VLAN_QOS_MAPPING,
 					    sizeof(m), &m))
 					goto nla_put_failure;
diff --git a/net/8021q/vlanproc.c b/net/8021q/vlanproc.c
index fa67374bda49..0e424e0895b7 100644
--- a/net/8021q/vlanproc.c
+++ b/net/8021q/vlanproc.c
@@ -262,15 +262,19 @@ static int vlandev_seq_show(struct seq_file *seq, void *offset)
 		   vlan->ingress_priority_map[7]);
 
 	seq_printf(seq, " EGRESS priority mappings: ");
+	rcu_read_lock();
 	for (i = 0; i < 16; i++) {
-		const struct vlan_priority_tci_mapping *mp
-			= vlan->egress_priority_map[i];
+		const struct vlan_priority_tci_mapping *mp =
+			rcu_dereference(vlan->egress_priority_map[i]);
 		while (mp) {
+			u16 vlan_qos = READ_ONCE(mp->vlan_qos);
+
 			seq_printf(seq, "%u:%d ",
-				   mp->priority, ((mp->vlan_qos >> 13) & 0x7));
-			mp = mp->next;
+				   mp->priority, ((vlan_qos >> 13) & 0x7));
+			mp = rcu_dereference(mp->next);
 		}
 	}
+	rcu_read_unlock();
 	seq_puts(seq, "\n");
 
 	return 0;