From 1a5e13a79b989c2ed56da227729709c732b46c3f Mon Sep 17 00:00:00 2001
From: Jukka Rissanen <jukka.rissanen@nordicsemi.no>
Date: Mon, 3 Mar 2025 14:45:34 +0200
Subject: [PATCH] net: if: Release the interface lock early when starting IPv4
 ACD

In order to avoid any mutex deadlocks between iface->lock and
TX lock, release the interface lock before calling a function
that will acquire TX lock. See previous commit for similar issue
in RS timer handling. So here we create a separate list of ACD
addresses that are to be started when network interface comes up
without iface->lock held.

Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>
---
 include/zephyr/net/net_if.h |  3 +++
 subsys/net/ip/net_if.c      | 31 ++++++++++++++++++++++++++++---
 2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/include/zephyr/net/net_if.h b/include/zephyr/net/net_if.h
index d1c106876fd..310ce39924e 100644
--- a/include/zephyr/net/net_if.h
+++ b/include/zephyr/net/net_if.h
@@ -112,6 +112,9 @@ struct net_if_addr {
 			/** Address conflict detection (ACD) timer. */
 			sys_snode_t acd_node;
 
+			/** ACD needed list node */
+			sys_snode_t acd_need_node;
+
 			/** ACD timeout value. */
 			k_timepoint_t acd_timeout;
 
diff --git a/subsys/net/ip/net_if.c b/subsys/net/ip/net_if.c
index f200339643a..219080dac08 100644
--- a/subsys/net/ip/net_if.c
+++ b/subsys/net/ip/net_if.c
@@ -4310,7 +4310,9 @@ void net_if_ipv4_start_acd(struct net_if *iface, struct net_if_addr *ifaddr)
 
 void net_if_start_acd(struct net_if *iface)
 {
+	struct net_if_addr *ifaddr, *next;
 	struct net_if_ipv4 *ipv4;
+	sys_slist_t acd_needed;
 	int ret;
 
 	net_if_lock(iface);
@@ -4332,6 +4334,11 @@ void net_if_start_acd(struct net_if *iface)
 
 	ipv4->conflict_cnt = 0;
 
+	/* Start ACD for all the addresses that were added earlier when
+	 * the interface was down.
+	 */
+	sys_slist_init(&acd_needed);
+
 	/* Start ACD for all the addresses that were added earlier when
 	 * the interface was down.
 	 */
@@ -4343,9 +4350,21 @@ void net_if_start_acd(struct net_if *iface)
 			continue;
 		}
 
-		net_if_ipv4_start_acd(iface, &ipv4->unicast[i].ipv4);
+		sys_slist_prepend(&acd_needed, &ipv4->unicast[i].ipv4.acd_need_node);
 	}
 
+	net_if_unlock(iface);
+
+	/* Start ACD for all the addresses without holding the iface lock
+	 * to avoid any possible mutex deadlock issues.
+	 */
+	SYS_SLIST_FOR_EACH_CONTAINER_SAFE(&acd_needed,
+					  ifaddr, next, acd_need_node) {
+		net_if_ipv4_start_acd(iface, ifaddr);
+	}
+
+	return;
+
 out:
 	net_if_unlock(iface);
 }
@@ -4439,7 +4458,8 @@ struct net_if_addr *net_if_ipv4_addr_add(struct net_if *iface,
 
 		if (!(l2_flags_get(iface) & NET_L2_POINT_TO_POINT) &&
 		    !net_ipv4_is_addr_loopback(addr)) {
-			net_if_ipv4_start_acd(iface, ifaddr);
+			/* ACD is started after the lock is released. */
+			;
 		} else {
 			ifaddr->addr_state = NET_ADDR_PREFERRED;
 		}
@@ -4449,7 +4469,12 @@ struct net_if_addr *net_if_ipv4_addr_add(struct net_if *iface,
 		net_mgmt_event_notify_with_info(NET_EVENT_IPV4_ADDR_ADD, iface,
 						&ifaddr->address.in_addr,
 						sizeof(struct in_addr));
-		goto out;
+
+		net_if_unlock(iface);
+
+		net_if_ipv4_start_acd(iface, ifaddr);
+
+		return ifaddr;
 	}
 
 out: