Subject: [PATCH v4] net: net_failover: Fix the deadlock in slave register

From: [email-masked]
Date: Mon, 11 May 2026 22:05:51 +0800

From: Faicker Mo <[email-masked]>

There is netdev_lock_ops() before the NETDEV_REGISTER notifier
in register_netdevice(), so use the non-locking functions
in net_failover_slave_register().
failover_slave_register() in failover_existing_slave_register() adds lock
and unlock ops too.

Call Trace:
 <TASK>
 __schedule+0x30d/0x7a0
 schedule+0x27/0x90
 schedule_preempt_disabled+0x15/0x30
 __mutex_lock.constprop.0+0x538/0x9e0
 __mutex_lock_slowpath+0x13/0x20
 mutex_lock+0x3b/0x50
 dev_set_mtu+0x40/0xe0
 net_failover_slave_register+0x24/0x280
 failover_slave_register+0x103/0x1b0
 failover_event+0x15e/0x210
 ? dropmon_net_event+0xac/0xe0
 notifier_call_chain+0x5e/0xe0
 raw_notifier_call_chain+0x16/0x30
 call_netdevice_notifiers_info+0x52/0xa0
 register_netdevice+0x5f4/0x7c0
 register_netdev+0x1e/0x40
 _mlx5e_probe+0xe2/0x370 [mlx5_core]
 mlx5e_probe+0x59/0x70 [mlx5_core]
 ? __pfx_mlx5e_probe+0x10/0x10 [mlx5_core]

Fixes: 4c975fd70002 ("net: hold instance lock during NETDEV_REGISTER/UP")
Signed-off-by: Faicker Mo <[email-masked]>
---
Changes since v1:
  - Fix the space chars (Simon)
  - Change the dev_close to netif_close (Simon)
  - Change the label err_dev_open to err_netif_open
Changes since v2:
  - Add lock ops in failover_existing_slave_register (Jakub Kicinski)
Changes since v3:
  - Fix the lock ops implicit declaration (Jakub Kicinski)
---
 drivers/net/net_failover.c | 12 ++++++------
 net/core/failover.c        |  6 +++++-
 2 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/drivers/net/net_failover.c b/drivers/net/net_failover.c
index d0361aaf25ef..3f7d31033bae 100644
--- a/drivers/net/net_failover.c
+++ b/drivers/net/net_failover.c
@@ -502,7 +502,7 @@ static int net_failover_slave_register(struct net_device *slave_dev,
 
 	/* Align MTU of slave with failover dev */
 	orig_mtu = slave_dev->mtu;
-	err = dev_set_mtu(slave_dev, failover_dev->mtu);
+	err = netif_set_mtu(slave_dev, failover_dev->mtu);
 	if (err) {
 		netdev_err(failover_dev, "unable to change mtu of %s to %u register failed\n",
 			   slave_dev->name, failover_dev->mtu);
@@ -512,11 +512,11 @@ static int net_failover_slave_register(struct net_device *slave_dev,
 	dev_hold(slave_dev);
 
 	if (netif_running(failover_dev)) {
-		err = dev_open(slave_dev, NULL);
+		err = netif_open(slave_dev, NULL);
 		if (err && (err != -EBUSY)) {
 			netdev_err(failover_dev, "Opening slave %s failed err:%d\n",
 				   slave_dev->name, err);
-			goto err_dev_open;
+			goto err_netif_open;
 		}
 	}
 
@@ -562,10 +562,10 @@ static int net_failover_slave_register(struct net_device *slave_dev,
 err_vlan_add:
 	dev_uc_unsync(slave_dev, failover_dev);
 	dev_mc_unsync(slave_dev, failover_dev);
-	dev_close(slave_dev);
-err_dev_open:
+	netif_close(slave_dev);
+err_netif_open:
 	dev_put(slave_dev);
-	dev_set_mtu(slave_dev, orig_mtu);
+	netif_set_mtu(slave_dev, orig_mtu);
 done:
 	return err;
 }
diff --git a/net/core/failover.c b/net/core/failover.c
index 11bb183c7a1b..e43c59cd6868 100644
--- a/net/core/failover.c
+++ b/net/core/failover.c
@@ -12,6 +12,7 @@
 #include <uapi/linux/if_arp.h>
 #include <linux/rtnetlink.h>
 #include <linux/if_vlan.h>
+#include <net/netdev_lock.h>
 #include <net/failover.h>
 
 static LIST_HEAD(failover_list);
@@ -221,8 +222,11 @@ failover_existing_slave_register(struct net_device *failover_dev)
 	for_each_netdev(net, dev) {
 		if (netif_is_failover(dev))
 			continue;
-		if (ether_addr_equal(failover_dev->perm_addr, dev->perm_addr))
+		if (ether_addr_equal(failover_dev->perm_addr, dev->perm_addr)) {
+			netdev_lock_ops(dev);
 			failover_slave_register(dev);
+			netdev_unlock_ops(dev);
+		}
 	}
 	rtnl_unlock();
 }
-- 
2.34.1