As usual, atomically accessed integer. The `espctl_vars' are more
complicated than already unlocked `ah_ctlvars' and `ipcomp_ctlvars',
so unlock them step-by-step.

Index: sys/net/pfkeyv2.c
===================================================================
RCS file: /cvs/src/sys/net/pfkeyv2.c,v
retrieving revision 1.267
diff -u -p -r1.267 pfkeyv2.c
--- sys/net/pfkeyv2.c	13 May 2025 09:16:33 -0000	1.267
+++ sys/net/pfkeyv2.c	14 May 2025 18:12:09 -0000
@@ -1068,7 +1068,7 @@ pfkeyv2_get_proto_alg(u_int8_t satype, u
 		break;
 
 	case SADB_SATYPE_ESP:
-		if (!esp_enable)
+		if (!atomic_load_int(&esp_enable))
 			return (EOPNOTSUPP);
 
 		*sproto = IPPROTO_ESP;
Index: sys/netinet/ipsec_input.c
===================================================================
RCS file: /cvs/src/sys/netinet/ipsec_input.c,v
retrieving revision 1.215
diff -u -p -r1.215 ipsec_input.c
--- sys/netinet/ipsec_input.c	14 May 2025 14:32:15 -0000	1.215
+++ sys/netinet/ipsec_input.c	14 May 2025 18:12:09 -0000
@@ -118,12 +118,15 @@ int ipsec_soft_first_use = IPSEC_DEFAULT
 int ipsec_exp_first_use = IPSEC_DEFAULT_EXP_FIRST_USE;		/* [a] */
 int ipsec_expire_acquire = IPSEC_DEFAULT_EXPIRE_ACQUIRE;	/* [a] */
 
-int esp_enable = 1;
+int esp_enable = 1;		/* [a] */
 int ah_enable = 1;		/* [a] */
 int ipcomp_enable = 0;		/* [a] */
 
 const struct sysctl_bounded_args espctl_vars[] = {
 	{ESPCTL_ENABLE, &esp_enable, 0, 1},
+};
+
+const struct sysctl_bounded_args espctl_vars_locked[] = {
 	{ESPCTL_UDPENCAP_ENABLE, &udpencap_enable, 0, 1},
 	{ESPCTL_UDPENCAP_PORT, &udpencap_port, 0, 65535},
 };
@@ -724,9 +727,13 @@ esp_sysctl(int *name, u_int namelen, voi
 	switch (name[0]) {
 	case ESPCTL_STATS:
 		return (esp_sysctl_espstat(oldp, oldlenp, newp));
+	case ESPCTL_ENABLE:
+		error = sysctl_bounded_arr(espctl_vars, nitems(espctl_vars),
+		    name, namelen, oldp, oldlenp, newp, newlen);
 	default:
 		NET_LOCK();
-		error = sysctl_bounded_arr(espctl_vars, nitems(espctl_vars),
+		error = sysctl_bounded_arr(espctl_vars_locked,
+		    nitems(espctl_vars_locked),
 		    name, namelen, oldp, oldlenp, newp, newlen);
 		NET_UNLOCK();
 		return (error);
@@ -876,7 +883,7 @@ esp46_input(struct mbuf **mp, int *offp,
 #if NPF > 0
 	    ((*mp)->m_pkthdr.pf.flags & PF_TAG_DIVERTED) ||
 #endif
-	    !esp_enable)
+	    !atomic_load_int(&esp_enable))
 		return ipsec_input_disabled(mp, offp, proto, af, ns);
 
 	protoff = ipsec_protoff(*mp, *offp, af);
Index: sys/netinet/ipsec_output.c
===================================================================
RCS file: /cvs/src/sys/netinet/ipsec_output.c,v
retrieving revision 1.101
diff -u -p -r1.101 ipsec_output.c
--- sys/netinet/ipsec_output.c	14 May 2025 14:32:15 -0000	1.101
+++ sys/netinet/ipsec_output.c	14 May 2025 18:12:09 -0000
@@ -91,7 +91,7 @@ ipsp_process_packet(struct mbuf *m, stru
 #endif
 
 	/* Check that the transform is allowed by the administrator. */
-	if ((tdb->tdb_sproto == IPPROTO_ESP && !esp_enable) ||
+	if ((tdb->tdb_sproto == IPPROTO_ESP && !atomic_load_int(&esp_enable)) ||
 	    (tdb->tdb_sproto == IPPROTO_AH && !atomic_load_int(&ah_enable)) ||
 	    (tdb->tdb_sproto == IPPROTO_IPCOMP &&
 	    !atomic_load_int(&ipcomp_enable))) {
Index: sys/netinet/udp_usrreq.c
===================================================================
RCS file: /cvs/src/sys/netinet/udp_usrreq.c,v
retrieving revision 1.337
diff -u -p -r1.337 udp_usrreq.c
--- sys/netinet/udp_usrreq.c	12 May 2025 17:21:21 -0000	1.337
+++ sys/netinet/udp_usrreq.c	14 May 2025 18:12:09 -0000
@@ -303,7 +303,7 @@ udp_input(struct mbuf **mp, int *offp, i
 	CLR(m->m_pkthdr.csum_flags, M_UDP_CSUM_OUT);
 
 #ifdef IPSEC
-	if (udpencap_enable && udpencap_port && esp_enable &&
+	if (udpencap_enable && udpencap_port && atomic_load_int(&esp_enable) &&
 #if NPF > 0
 	    !(m->m_pkthdr.pf.flags & PF_TAG_DIVERTED) &&
 #endif