FAILED: patch "[PATCH] 8021q: delete cleared egress QoS mappings" failed to apply to 6.12-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 6.12-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x 7dddc74af369478ba7f9bc136d0fc1dc4570cb66
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026050409-guts-implode-5a2a@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 7dddc74af369478ba7f9bc136d0fc1dc4570cb66 Mon Sep 17 00:00:00 2001
From: Longxuan Yu <ylong030@ucr.edu>
Date: Mon, 20 Apr 2026 11:18:46 +0800
Subject: [PATCH] 8021q: delete cleared egress QoS mappings

vlan_dev_set_egress_priority() currently keeps cleared egress
priority mappings in the hash as tombstones. Repeated set/clear cycles
with distinct skb priorities therefore accumulate mapping nodes until
device teardown and leak memory.

Delete mappings when vlan_prio is cleared instead of keeping tombstones.
Now that the egress mapping lists are RCU protected, the node can be
unlinked safely and freed after a grace period.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@kernel.org
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
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/ecfa6f6ce2467a42647ff4c5221238ae85b79a59.1776647968.git.yuantan098@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/net/8021q/vlan_dev.c b/net/8021q/vlan_dev.c
index a5340932b657..7aa3af8b10ea 100644
--- a/net/8021q/vlan_dev.c
+++ b/net/8021q/vlan_dev.c
@@ -172,26 +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 __rcu **mpp;
 	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 = rtnl_dereference(vlan->egress_priority_map[bucket]);
+	mpp = &vlan->egress_priority_map[bucket];
+	mp = rtnl_dereference(*mpp);
 	while (mp) {
 		if (mp->priority == skb_prio) {
-			if (mp->vlan_qos && !vlan_qos)
+			if (!vlan_qos) {
+				rcu_assign_pointer(*mpp, rtnl_dereference(mp->next));
 				vlan->nr_egress_mappings--;
-			else if (!mp->vlan_qos && vlan_qos)
-				vlan->nr_egress_mappings++;
-			WRITE_ONCE(mp->vlan_qos, vlan_qos);
+				kfree_rcu(mp, rcu);
+			} else {
+				WRITE_ONCE(mp->vlan_qos, vlan_qos);
+			}
 			return 0;
 		}
-		mp = rtnl_dereference(mp->next);
+		mpp = &mp->next;
+		mp = rtnl_dereference(*mpp);
 	}
 
 	/* Create a new mapping then. */
+	if (!vlan_qos)
+		return 0;
+
 	np = kmalloc_obj(struct vlan_priority_tci_mapping);
 	if (!np)
 		return -ENOBUFS;
diff --git a/net/8021q/vlan_netlink.c b/net/8021q/vlan_netlink.c
index a5b16833e2ce..368d53ca7d87 100644
--- a/net/8021q/vlan_netlink.c
+++ b/net/8021q/vlan_netlink.c
@@ -263,10 +263,6 @@ static int vlan_fill_info(struct sk_buff *skb, const struct net_device *dev)
 			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   = (vlan_qos >> 13) & 0x7;
 				if (nla_put(skb, IFLA_VLAN_QOS_MAPPING,