ipv6: anycast: Don't use rtnl_dereference().

JIRA: https://issues.redhat.com/browse/RHEL-115325

commit 7b6b53a
Author: Kuniyuki Iwashima <kuniyu@google.com>
Date:   Wed Jul 2 16:01:28 2025 -0700

    ipv6: anycast: Don't use rtnl_dereference().

    inet6_dev->ac_list is protected by inet6_dev->lock, so rtnl_dereference()
    is a bit rough annotation.

    As done in mcast.c, we can use ac_dereference() that checks if
    inet6_dev->lock is held.

    Let's replace rtnl_dereference() with a new helper ac_dereference().

    Note that now addrconf_join_solict() / addrconf_leave_solict() in
    __ipv6_dev_ac_inc() / __ipv6_dev_ac_dec() does not need RTNL, so we
    can remove ASSERT_RTNL() there.

    Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
    Reviewed-by: Eric Dumazet <edumazet@google.com>
    Link: https://patch.msgid.link/20250702230210.3115355-12-kuni1840@gmail.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>

Author: CKI Backport Bot

net/ipv6/addrconf.c

@@ -2251,7 +2251,6 @@ void addrconf_leave_solict(struct inet6_dev *idev, const struct in6_addr *addr)
 	__ipv6_dev_mc_dec(idev, &maddr);
 }
 
-/* caller must hold RTNL */
 static void addrconf_join_anycast(struct inet6_ifaddr *ifp)
 {
 	struct in6_addr addr;
@@ -2264,7 +2263,6 @@ static void addrconf_join_anycast(struct inet6_ifaddr *ifp)
 	__ipv6_dev_ac_inc(ifp->idev, &addr);
 }
 
-/* caller must hold RTNL */
 static void addrconf_leave_anycast(struct inet6_ifaddr *ifp)
 {
 	struct in6_addr addr;

net/ipv6/anycast.c

@@ -47,6 +47,9 @@
 static struct hlist_head inet6_acaddr_lst[IN6_ADDR_HSIZE];
 static DEFINE_SPINLOCK(acaddr_hash_lock);
 
+#define ac_dereference(a, idev)						\
+	rcu_dereference_protected(a, lockdep_is_held(&(idev)->lock))
+
 static int ipv6_dev_ac_dec(struct net_device *dev, const struct in6_addr *addr);
 
 static u32 inet6_acaddr_hash(const struct net *net,
@@ -319,16 +322,14 @@ int __ipv6_dev_ac_inc(struct inet6_dev *idev, const struct in6_addr *addr)
 	struct net *net;
 	int err;
 
-	ASSERT_RTNL();
-
 	write_lock_bh(&idev->lock);
 	if (idev->dead) {
 		err = -ENODEV;
 		goto out;
 	}
 
-	for (aca = rtnl_dereference(idev->ac_list); aca;
-	     aca = rtnl_dereference(aca->aca_next)) {
+	for (aca = ac_dereference(idev->ac_list, idev); aca;
+	     aca = ac_dereference(aca->aca_next, idev)) {
 		if (ipv6_addr_equal(&aca->aca_addr, addr)) {
 			aca->aca_users++;
 			err = 0;
@@ -380,12 +381,10 @@ int __ipv6_dev_ac_dec(struct inet6_dev *idev, const struct in6_addr *addr)
 {
 	struct ifacaddr6 *aca, *prev_aca;
 
-	ASSERT_RTNL();
-
 	write_lock_bh(&idev->lock);
 	prev_aca = NULL;
-	for (aca = rtnl_dereference(idev->ac_list); aca;
-	     aca = rtnl_dereference(aca->aca_next)) {
+	for (aca = ac_dereference(idev->ac_list, idev); aca;
+	     aca = ac_dereference(aca->aca_next, idev)) {
 		if (ipv6_addr_equal(&aca->aca_addr, addr))
 			break;
 		prev_aca = aca;
@@ -429,7 +428,7 @@ void ipv6_ac_destroy_dev(struct inet6_dev *idev)
 	struct ifacaddr6 *aca;
 
 	write_lock_bh(&idev->lock);
-	while ((aca = rtnl_dereference(idev->ac_list)) != NULL) {
+	while ((aca = ac_dereference(idev->ac_list, idev)) != NULL) {
 		rcu_assign_pointer(idev->ac_list, aca->aca_next);
 		write_unlock_bh(&idev->lock);