[SRU][N][PATCH 2/2] bonding: do not set usable_slaves for broadcast mode

[Edoardo Canepa]

From: Hangbin Liu <liuhangbin at gmail.com>

BugLink: https://bugs.launchpad.net/bugs/2153556

After commit e0caeb24f538 ("net: bonding: update the slave array for broadcast mode"),
broadcast mode will also set all_slaves and usable_slaves during
bond_enslave(). But if we also set updelay, during enslave, the
slave init state will be BOND_LINK_BACK. And later
bond_update_slave_arr() will alloc usable_slaves but add nothing.
This will cause bond_miimon_inspect() to have ignore_updelay
always true. So the updelay will be always ignored. e.g.

[    6.498368] bond0: (slave veth2): link status definitely down, disabling slave
[    7.536371] bond0: (slave veth2): link status up, enabling it in 0 ms
[    7.536402] bond0: (slave veth2): link status definitely up, 10000 Mbps full duplex

To fix it, we can either always call bond_update_slave_arr() on every
place when link changes. Or, let's just not set usable_slaves for
broadcast mode.

Fixes: e0caeb24f538 ("net: bonding: update the slave array for broadcast mode")
Reported-by: Liang Li <liali at redhat.com>
Signed-off-by: Hangbin Liu <liuhangbin at gmail.com>
Link: https://patch.msgid.link/20260304-b4-bond_updelay-v1-1-f72eb2e454d0@gmail.com
Signed-off-by: Jakub Kicinski <kuba at kernel.org>
(cherry picked from commit 45fc134bcfadde456639c1b1e206e6918d69a553)
Signed-off-by: Edoardo Canepa <edoardo.canepa at canonical.com>
---
 drivers/net/bonding/bond_main.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 93ef49ad6273..f06b03ce55e3 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -5124,13 +5124,18 @@ static void bond_set_slave_arr(struct bonding *bond,
 {
 	struct bond_up_slave *usable, *all;
 
-	usable = rtnl_dereference(bond->usable_slaves);
-	rcu_assign_pointer(bond->usable_slaves, usable_slaves);
-	kfree_rcu(usable, rcu);
-
 	all = rtnl_dereference(bond->all_slaves);
 	rcu_assign_pointer(bond->all_slaves, all_slaves);
 	kfree_rcu(all, rcu);
+
+	if (BOND_MODE(bond) == BOND_MODE_BROADCAST) {
+		kfree_rcu(usable_slaves, rcu);
+		return;
+	}
+
+	usable = rtnl_dereference(bond->usable_slaves);
+	rcu_assign_pointer(bond->usable_slaves, usable_slaves);
+	kfree_rcu(usable, rcu);
 }
 
 static void bond_reset_slave_arr(struct bonding *bond)
-- 
2.51.0