[PATCH 6.12 455/567] net: macb: Relocate mog_init_rings() callback from macb_mac_link_up() to macb_open()

Greg Kroah-Hartman
2026-01-06T17:41:47Z

From: Xiaolei Wang <xiaolei.wang@windriver.com>

commit 99537d5c476cada9cf75aef9fa75579a31faadb9 upstream.

In the non-RT kernel, local_bh_disable() merely disables preemption,
whereas it maps to an actual spin lock in the RT kernel. Consequently,
when attempting to refill RX buffers via netdev_alloc_skb() in
macb_mac_link_up(), a deadlock scenario arises as follows:

WARNING: possible circular locking dependency detected
6.18.0-08691-g2061f18ad76e #39 Not tainted
------------------------------------------------------
kworker/0:0/8 is trying to acquire lock:
ffff00080369bbe0 (&bp->lock){+.+.}-{3:3}, at: macb_start_xmit+0x808/0xb7c

but task is already holding lock:
ffff000803698e58 (&queue->tx_ptr_lock){+...}-{3:3}, at: macb_start_xmit
+0x148/0xb7c

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #3 (&queue->tx_ptr_lock){+...}-{3:3}:
rt_spin_lock+0x50/0x1f0
macb_start_xmit+0x148/0xb7c
dev_hard_start_xmit+0x94/0x284
sch_direct_xmit+0x8c/0x37c
__dev_queue_xmit+0x708/0x1120
neigh_resolve_output+0x148/0x28c
ip6_finish_output2+0x2c0/0xb2c
__ip6_finish_output+0x114/0x308
ip6_output+0xc4/0x4a4
mld_sendpack+0x220/0x68c
mld_ifc_work+0x2a8/0x4f4
process_one_work+0x20c/0x5f8
worker_thread+0x1b0/0x35c
kthread+0x144/0x200
ret_from_fork+0x10/0x20

-> #2 (_xmit_ETHER#2){+...}-{3:3}:
rt_spin_lock+0x50/0x1f0
sch_direct_xmit+0x11c/0x37c
__dev_queue_xmit+0x708/0x1120
neigh_resolve_output+0x148/0x28c
ip6_finish_output2+0x2c0/0xb2c
__ip6_finish_output+0x114/0x308
ip6_output+0xc4/0x4a4
mld_sendpack+0x220/0x68c
mld_ifc_work+0x2a8/0x4f4
process_one_work+0x20c/0x5f8
worker_thread+0x1b0/0x35c
kthread+0x144/0x200
ret_from_fork+0x10/0x20

-> #1 ((softirq_ctrl.lock)){+.+.}-{3:3}:
lock_release+0x250/0x348
__local_bh_enable_ip+0x7c/0x240
__netdev_alloc_skb+0x1b4/0x1d8
gem_rx_refill+0xdc/0x240
gem_init_rings+0xb4/0x108
macb_mac_link_up+0x9c/0x2b4
phylink_resolve+0x170/0x614
process_one_work+0x20c/0x5f8
worker_thread+0x1b0/0x35c
kthread+0x144/0x200
ret_from_fork+0x10/0x20

-> #0 (&bp->lock){+.+.}-{3:3}:
__lock_acquire+0x15a8/0x2084
lock_acquire+0x1cc/0x350
rt_spin_lock+0x50/0x1f0
macb_start_xmit+0x808/0xb7c
dev_hard_start_xmit+0x94/0x284
sch_direct_xmit+0x8c/0x37c
__dev_queue_xmit+0x708/0x1120
neigh_resolve_output+0x148/0x28c
ip6_finish_output2+0x2c0/0xb2c
__ip6_finish_output+0x114/0x308
ip6_output+0xc4/0x4a4
mld_sendpack+0x220/0x68c
mld_ifc_work+0x2a8/0x4f4
process_one_work+0x20c/0x5f8
worker_thread+0x1b0/0x35c
kthread+0x144/0x200
ret_from_fork+0x10/0x20

other info that might help us debug this:

Chain exists of:
&bp->lock --> _xmit_ETHER#2 --> &queue->tx_ptr_lock

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&queue->tx_ptr_lock);
lock(_xmit_ETHER#2);
lock(&queue->tx_ptr_lock);
lock(&bp->lock);

*** DEADLOCK ***

Call trace:
show_stack+0x18/0x24 (C)
dump_stack_lvl+0xa0/0xf0
dump_stack+0x18/0x24
print_circular_bug+0x28c/0x370
check_noncircular+0x198/0x1ac
__lock_acquire+0x15a8/0x2084
lock_acquire+0x1cc/0x350
rt_spin_lock+0x50/0x1f0
macb_start_xmit+0x808/0xb7c
dev_hard_start_xmit+0x94/0x284
sch_direct_xmit+0x8c/0x37c
__dev_queue_xmit+0x708/0x1120
neigh_resolve_output+0x148/0x28c
ip6_finish_output2+0x2c0/0xb2c
__ip6_finish_output+0x114/0x308
ip6_output+0xc4/0x4a4
mld_sendpack+0x220/0x68c
mld_ifc_work+0x2a8/0x4f4
process_one_work+0x20c/0x5f8
worker_thread+0x1b0/0x35c
kthread+0x144/0x200
ret_from_fork+0x10/0x20

Notably, invoking the mog_init_rings() callback upon link establishment
is unnecessary. Instead, we can exclusively call mog_init_rings() within
the ndo_open() callback. This adjustment resolves the deadlock issue.
Furthermore, since MACB_CAPS_MACB_IS_EMAC cases do not use mog_init_rings()
when opening the network interface via at91ether_open(), moving
mog_init_rings() to macb_open() also eliminates the MACB_CAPS_MACB_IS_EMAC
check.

Fixes: 633e98a711ac ("net: macb: use resolved link config in mac_link_up()")
Cc: stable@vger.kernel.org
Suggested-by: Kevin Hao <kexin.hao@windriver.com>
Signed-off-by: Xiaolei Wang <xiaolei.wang@windriver.com>
Link: https://patch.msgid.link/20251222015624.1994551-1-xiaolei.wang@windriver.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/ethernet/cadence/macb_main.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/net/ethernet/cadence/macb_main.c
+++ b/drivers/net/ethernet/cadence/macb_main.c
@@ -759,7 +759,6 @@ static void macb_mac_link_up(struct phyl
/* Initialize rings & buffers as clearing MACB_BIT(TE) in link down
* cleared the pipeline and control registers.
*/
- bp->macbgem_ops.mog_init_rings(bp);
macb_init_buffers(bp);

for (q = 0, queue = bp->queues; q < bp->num_queues; ++q, ++queue)
@@ -2985,6 +2984,8 @@ static int macb_open(struct net_device *
goto pm_exit;
}

+ bp->macbgem_ops.mog_init_rings(bp);
+
for (q = 0, queue = bp->queues; q < bp->num_queues; ++q, ++queue) {
napi_enable(&queue->napi_rx);
napi_enable(&queue->napi_tx);